Exp Appl Acarol DOI 10.1007/s10493-014-9862-3
Evaluation of various types of supplemental food for two species of predatory mites, Amblyseius swirskii and Neoseiulus cucumeris (Acari: Phytoseiidae) J. F. Delisle • J. Brodeur • L. Shipp
Received: 28 November 2013 / Accepted: 6 November 2014 Ó Her Majesty the Queen in Right of Canada 2014
Abstract Although phytoseiids are best known as predators of phytophagous mites and other small arthropods, several species can also feed and reproduce on pollen. In laboratory assays, we assessed the profitability of two types of dietary supplements (three pollen species—cattail, maize and apple—and eggs of the Mediterranean flour moth, Ephestia kuehniella) for the two species of predatory mites most commonly used as biocontrol agents in horticulture in Canada, Neoseiulus cucumeris and Amblyseius swirskii. We measured the effects of each diet on phytoseiid fitness parameters (survival, development, sex ratio, fecundity) and, as a means of comparison, when fed larvae of the common targeted pest species, western flower thrips Frankliniella occidentalis. A soluble protein assay was also performed on the alternative food sources as protein content is often linked to high nutritive value according to the literature. All food sources tested were suitable for N. cucumeris and A. swirskii, both species being able to develop from egg to adult. The dietary supplements had a beneficial impact on biological parameters, mostly resulting in shorter development times and higher survival rates when compared to thrips larvae. Amblyseius swirskii exhibited a wider dietary range than N. cucumeris. Overall, flour moth eggs, cattail pollen and apple pollen are food sources of equal quality for A. swirskii, whereas apple and cattail pollen are better when it comes to N. cucumeris. In contrast, maize pollen is a less suitable food source for N. cucumeris and A. swirskii. Soluble protein content results did not match the prediction under which the most beneficial food source would contain the highest concentration in protein.
J. F. Delisle J. Brodeur (&) De´partement de Sciences Biologiques, Institut de Recherche en Biologie Ve´ge´tale, Universite´ de Montre´al, Montreal, QC H1X 2B2, Canada e-mail: [email protected] L. Shipp Agriculture and Agri-Food Canada, Greenhouse and Processing Crops Research Centre, Harrow, ON N0R 1G0, Canada e-mail: [email protected]
123
Exp Appl Acarol
Keywords Alternative food sources Pollen Ephestia kuehniella egg Frankliniella occidentalis Life history parameters Biological control
Introduction Plants can provide non-prey foods to predators of herbivorous arthropods, an adaptation that may facilitate protection against herbivory by increasing the performance of natural enemies (van Rijn et al. 2002; van Rijn and Sabelis 2005; Lundgren 2009). Several phytoseiids, a large family of predatory mites broadly used as biocontrol agents, are mainly described as predators of phytophagous mites and small arthropods. However, many plantinhabiting phytoseiid mites can feed and reproduce on pollen as well (McMurtry and Scriven 1964; Tanigoshi 1981; McMurtry and Croft 1997). Phytoseiid mite species clearly differ in their propensity/capacity to use pollen and their developmental and reproductive responses to different pollen sources can vary considerably (Kostiainen and Hoy 1996; McMurtry and Croft 1997; Goleva and Zebitz 2013; Ranabhat et al. 2014). Pollen serves as a dietary supplement to prey of low quality or when prey are rare or absent (McMurtry and Croft 1997; Tuovinen and Lindqvist 2010). Pollen is also considered as the favorite food source for immature stages of several phytoseiid mites (Vantornhout et al. 2004). Moreover, McMurtry and Rodriguez (1987) compiled a list of phytoseiids that reproduce better on pollen than on prey. In a biological control context, their ability to feed on pollen allows predatory mites to increase survival during periods of prey scarcity and retention in the crop (van Houten and van Stratum 1995). Accordingly, pollen has long been recognized as an important factor in the success of biological control of whiteflies (Nomikou et al. 2010), thrips (Ramakers 1990; van Rijn et al. 1999), and spider mites (McMurtry and Croft 1997; Maoz et al. 2008), although the most successful predators of Tetranychidae do not feed on pollen (e.g., Phytoseiulus persimilis AthiasHenriot). Supplementary food sources other than that derived from plants have also been investigated for predatory mites. These factitious prey include sterilized eggs of the Mediterranean flour moth (MFM), Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) and cysts of the brine shrimp, Artemia franciscana Kellogg (Branchiopoda: Artemiidae) (Romeih et al. 2004; Vantornhout et al. 2004; Momen and El-Laithy 2007; Nguyen et al. 2014; Vangansbeke et al. 2014). These are frequently used as an alternative food source for insect natural enemies alone, as part of a mixed diet or as a factitious host (e.g., Cohen and Smith 1998; De Clercq et al. 2005; Bonte and De Clercq 2008; Vandekerkhove et al. 2009). In this study, we compared the profitability of different types of alternative food sources, vegetable and animal, that have been proven to be amongst the more suitable for phytoseiids: cattail (Typha latifolia L.), apple (Malus domestica L.) and maize (Zea mays L.) pollen, as well as MFM eggs. These food sources have been chosen according to several prerequisites: accessibility of the food source, storage capacity without alteration of the nutritive quality, known beneficial effects on phytoseiid fitness and potential for subsequent agricultural use in greenhouse crops. The life history characteristics of commercially available Amblyseius swirskii Athias-Henriot and Neoseiulus cucumeris (Oudemans) were determined when fed these dietary supplements, as well as western flower thrips first instars [Frankliniella occidentalis (Pergande)], a common targeted pest
123
Exp Appl Acarol
species for both phytoseiid species. In addition, the nutritional quality of each supplemental food source was partly assessed through biochemical analysis of their soluble protein content, which represents the proteins available to the predatory mites according to their feeding behavior (Flechtmann and McMurtry 1992).
Materials and methods Arthropod cultures Colonies of predatory mites were established from individuals obtained from Biobest Canada (Leamington, ON) and maintained in two separate growth chambers at 25 °C, 65–80 % RH and 16L:8D photoperiod. Phytoseiids were reared on individual Lima bean plant stems, infested with two-spotted spider mites (Tetranychus urticae Koch), maintained on a wire mesh in plastic tanks of 50-l capacity (58.4 9 39 9 29.8 cm) filled with water. The roots of the stems were in constant contact with the water while the foliage stayed dry, allowing the mites to proliferate in a healthy environment. The upper edge of each basin was coated with TanglefootÒ glue and placed on a tray filled with water to prevent contamination. A population of western flower thrips, collected from a hibiscus (Hibiscus sp.) greenhouse at the Botanical Garden of Montre´al (Canada), was maintained on potted chrysanthemum plants cv. Butterfield (Planterra, Dorval, QC, Canada) in a growth chamber at 25 °C, 60 % RH and 16L:8D photoperiod. Dietary supplements Eggs of MFM were provided by the Horticulture Research and Development Centre (StJean-sur-Richelieu, QC, Canada). Fresh eggs (\24 h) were killed and sterilized in a freezer (-15 °C for 24 h) and refrigerated (4 °C) for up to 2 weeks before the trials. Cattail pollen was harvested in June 2011 at the Montre´al Botanical Garden, whereas maize pollen (Zea mays L.) was harvested in July 2011 in a maize field at the CE´ROM Grain Research Center (St-Mathieu-de-Beloeil, QC, Canada). Apple pollen (cv. red delicious) was purchased from Firman Pollen (Yakima, WA, USA). The different pollens after collection or receipt were immediately transferred into small vials which were placed in a jar containing a color indicator desiccant agent (DrieriteÒ) and then frozen at -20 °C for long-term storage or refrigerated (4 °C) for up to 2 weeks during the experiments (van Rijn and Tanigoshi 1999). Experimental conditions and treatments The experimental unit was a Lima bean leaf disc (2 cm diameter) placed upside down on WhatmanÒ filter paper saturated with water, inside a Petri dish (4 cm diameter) covered with a lid. The lid contained a small venting hole to keep a suitable humidity level inside the dish. The Petri dishes were placed in a growth chamber at 25 °C, 60–70 % RH and 16L:8D photoperiod. A small piece of brown paper was placed in the center of the leaf disc as a refuge and oviposition site. It also prevented the mites from leaving the leaf disc and drowning, especially N. cucumeris (Arthurs et al. 2009). Individuals were transferred to a new arena every day, containing a fresh leaf disc and food source according to the treatment. The development time of each developmental stage, survival rate to adulthood,
123
Exp Appl Acarol
escape rate (see below), oviposition rate and the secondary sex ratio (proportion of females in the progeny) of A. swirskii and N. cucumeris were determined when fed with alternative food sources or thrips larvae. The ten experimental treatments included: predator ? prey (A. swirskii ? thrips larvae and N. cucumeris ? thrips larvae) and predator ? supplemental food (A. swirskii ? flour moth eggs; A. swirskii ? maize pollen; A. swirskii ? cattail pollen; A. swirskii ? apple pollen; N. cucumeris ? flour moth eggs; N. cucumeris ? maize pollen; N. cucumeris ? cattail pollen and N. cucumeris ? apple pollen). Three repetitions (blocks) were completed over time and at the beginning of each block and for each phytoseiid species, a total of 60 gravid females were collected from the rearing culture and placed on leaves infested by spider mites in Petri dishes. After 12 h, 40 eggs per species were individually transferred to experimental arenas to obtain an initial number of eight eggs per treatment. Three blocks were completed to obtain 24 replicates per treatment. Development time, survival rate and escape rate Every 12 h, phytoseiid eggs were checked for hatching. After hatching, the immature predatory mites were fed ad libitum daily with the dietary supplement according to the treatment [0.05 mg of pollen (following preliminary tests), 10 MFM eggs (following Vantornhout et al. 2004) or 10 first instar thrips (following Arthurs et al. 2009)]. The presence of an exuvium was verified every 12 h, indicating the transition to a new stage (van Rijn and Tanigoshi 1999). Development time of each stage, from egg to adult, was calculated in hours. Death of individuals was set at the mid-point between the last observation alive and the first record of death. The survival rate to adulthood was calculated as well as the escape rate, i.e., when the mites escaped the leaf disc and were drowned or not retrieved. After the experiment, each individual was mounted on a slide and observed under a microscope for sex determination. Oviposition rate and sex ratio Following Momen and El-Laithy (2007), during the last day of the deutonymph stage each female was placed with a male from the rearing colony for 24 h. Each mated female was then fed ad libitum as described previously for each treatment. The duration of the adult pre-oviposition period was determined (time between the third molt, marking the beginning of adulthood, and the first egg laid). Because the rate of oviposition typically reaches a stable level after 3 days (van Rijn and Tanigoshi 1999), eggs laid on days 4 and 5 were counted and removed after each observation interval of 12 h. Those eggs were then placed on an isolated leaf disc in a Petri dish and raised to adulthood on cattail pollen. The adults were then sexed to determine the secondary sex ratio. Cattail pollen was used because it is suitable for both predatory mites, thus avoiding differential mortality of the offspring before sex determination. In the two predator ? prey treatments, we cannot rule out the possibility that some eggs of the predator were killed by thrips larvae. In addition to being phytophagous, all active stages of F. occidentalis have the capacity to feed on eggs of various species of phytoseiids (Faraji et al. 2001; Janssen et al. 2002). However, predatory mites have been shown to display anti-predator behaviour against F. occidentalis to protect mite eggs by depositing them away from the thrips larvae (Magalha˜es et al. 2005; de Almeida and Janssen 2013). Thus, predation of mite eggs by first instars could have occurred, but such a pattern should be reduced to a minimum due to the presence of the
123
Exp Appl Acarol
adult mite, removal of eggs every 12 h, presence of a small refuge for oviposition, and because small and less voracious first instar thrips were used in our tests. Protein assay Soluble protein content of supplemental food items was measured using the Bradford method (Roulston et al. 2000). A standard calibration curve was initially performed with BSA (bovine serum albumin) in concentrations ranging from 0 to 0.02 g/l. To do that, 0.7 g of each dietary supplement was ground and then transferred into a vial containing 2.5 ml of extraction buffer (Tris HCl) (25 mM). The pH was adjusted to 7.5 (cytosolic). The mixture was centrifuged at 1,200–1,500g, supernatant removed and the solution was re-suspended to fill aliquots of 250 ll containing 200 ll of Bradford reagent and volumes ranging from 0 to 50 ll sample. Following incubation for 10 min at room temperature, the proteins were measured by reading the plate at 595 nm. Statistical analysis Due to the nature of the data acquisition of development time for each stage (intervals of 12 h), the distribution presents a modal numeric response and was analyzed using a Kruskal–Wallis test. A non-parametric post hoc comparison was performed with a Sidak correction to control comparison-wise error. Adjusted means for survival rates to adulthood and escape rates were calculated and analyzed with a log-linear analysis of frequency tables. The daily oviposition rates were analyzed using a one-way ANOVA. Model effects included block, treatment and their interaction. Block was set as a random effect. Tukey’s honestly significant difference (HSD) test was performed to determine the differences of least squares to an alpha error threshold of 5 %. The protein content data was compared between supplemental foods using a Kruskal–Wallis one-way test, followed by a nonparametric post hoc comparison with a Sidak correction.
Results Survival rate, escape rate and development time For A. swirskii and N. cucumeris, both sexes were analysed together because there was no significant difference between males and females for each developmental stage (Wilcoxon test, a = 0.05). Both predatory mite species developed to adult stage on every food source and immature survival rate, as well as escape rate, were not different among treatments (Table 1). For all food sources, developmental time of N. cucumeris was similar during the egg and larval stages (Table 1). Similarly, no difference was found among treatments in developmental time of egg, larva and protonymph of A. swirskii. For both species, the effects of the food source were the most pronounced during the protonymph or deutonymphal stages. For N. cucumeris, the shortest development times from egg to adult were observed when fed with cattail and apple pollen. For A. swirskii, the same trend was observed, as the cattail and apple pollen diets, as well as the MFM eggs diet, led to the shortest egg to adult development times.
123
123
1.39 ± 0.17a
95.8a
0a
Pre-oviposition
Survival (%)
Escape (%)
1.17 ± 0.10ab
5.05 ± 0.10ab
Deutonymph
Total
3.4a
100a
1.41 ± 0.17a
4.87 ± 0.17b
1.13 ± 0.10ab
1.29 ± 0.12a
0.55 ± 0.05a
0.57 ± 0.05a
1.43 ± 0.12a
Larvae
Protonymph
1.92 ± 0.08a
12.5a
87.5a
1.90 ± 0.08a
20.8a
Escape (%)
Egg
70.8a
Survival (%)
1.29 ± 0.21b
9.39 ± 0.60a
9.21 ± 0.57a
1.85 ± 0.24ab
Total
Pre-oviposition
4.53 ± 0.57a 2.32 ± 0.32a
3.95 ± 0.55a
2.77 ± 0.29a
Protonymph
Deutonymph
1.97 ± 0.07a 0.53 ± 0.07a
1.97 ± 0.07a
0.53 ± 0.06a
Egg
Larva
1.89 ± 0.07a
13.8a
95.8a
1.88 ± 0.17a
5.41 ± 0.10a
1.47 ± 0.11a
1.38 ± 0.12a
0.60 ± 0.05a
1.96 ± 0.09a
16.7a
79.2a
3.02 ± 0.22a
7.46 ± 0.61a
2.53 ± 0.31a
2.61 ± 0.58ab
0.62 ± 0.07a
2.05 ± 0.07a
3.6a
100a
1.41 ± 0.17a
4.58 ± 0.11b
0.95 ± 0.11b
1.27 ± 0.12a
0.56 ± 0.05a
1.85 ± 0.10a
8.3a
87.5a
1.24 ± 0.19b
5.66 ± 0.63b
1.40 ± 0.33a
1.62 ± 0.58bc
0.52 ± 0.07a
10.7a
100a
1.32 ± 0.18a
4.58 ± 0.11b
1.02 ± 0.10b
1.15 ± 0.12a
0.60 ± 0.05a
1.81 ± 0.09a
0a
95.8a
1.28 ± 0.20b
5.73 ± 0.62b
1.52 ± 0.35a
1.74 ± 0.57c
0.63 ± 0.08a
1.94 ± 0.08a
Apple pollen 6.62
0.16
0.14
v2 = 8.41 1.55
0.82
0.021 0.45 0.14
11.61 v2 = 6.88
\ 0.0001
0.0001
0.024
v2 = 3.69
43.50
22.92
11.29
0.64
0.15
v2 = 6.79 2.50
\ 0.0001
\ 0.0001
\ 0.0001
\ 0.0001
0.63
33.69
60.41
33.31
62.97
2.60
P
Survival rate to adulthood and escape rate are expressed in percentage of adjusted means. For each treatment, an initial number of 24 eggs were used (3 replicates 9 8 individuals). Total number of individuals included in the analysis: n = 120 (N. cucumeris) and 138 (A. swirskii). For each species, means within rows followed by different letters are significantly different (non-parametric post-hoc comparison with a Sidak correction for developmental durations, v2 test for escape and survival rates)
A. swirskii
N. cucumeris
Cattail pollen
H
Maize pollen
Thrips larvae
Flour moth eggs
Statistics (df = 4)
Food source
Table 1 Mean (± SE) duration (days) of Neoseiulus cucumeris and Amblyseius swirskii developmental and pre-oviposition period when reared on different diets at 25 °C
Exp Appl Acarol
Exp Appl Acarol
Oviposition rate and sex ratio The oviposition rate of N. cucumeris females was similar among treatments, except when fed on maize pollen which was at least 8 9 lower than for other food sources (F4,9 = 8.53, P \ 0.001; Fig. 1). For A. swirskii, maize pollen and thrips larvae resulted in the lowest oviposition rates (F4,5 = 5.16, P = 0.002; Fig. 2). For each predatory mite species, secondary sex ratios were similar among treatments (N. cucumeris, v2 = 0.75, P = 0.94; A. swirskii, v2 = 2.16, P = 0.71; both df = 4) (Table 2). Protein content Soluble protein content varied greatly among supplemental food items (F3,3 = 45, P \ 0.0001). Concentrations were the lowest in cattail pollen (4.5 ± 0.38 mg/g), intermediate in apple (26.5 ± 3.57 mg/g) and maize pollen (38.6 ± 0.60 mg/g) and maximum in flour moth eggs (45.6 ± 1.18 mg/g).
Discussion All food sources tested were suitable for N. cucumeris and A. swirskii. Both species were able to develop and reproduce when fed pollen (maize, cattail and apple) or MFM eggs. These food items were more suitable, mostly in terms of immature development, than first instars of the common targeted pest species, F. occidentalis. However, significant differences among food sources and between species were found. Amblyseius swirskii exhibited a wider dietary range than N. cucumeris, being able to develop rapidly when fed most diets, except thrips larvae and maize pollen, the latter resulting in the lowest oviposition rate. Overall, MFM eggs, cattail pollen and apple pollen are food sources of equal quality for A. swirskii, whereas apple and cattail pollen are better when it comes to N. cucumeris. The differences observed between the two species may result from their efficiency to convert food into eggs and their intrinsic capacity to feed on different food items given the morphology of predatory mite mouth appendages (Flechtmann and McMurtry 1992). For example, juvenile stages of N. cucumeris had difficulty to feed on intact MFM eggs,
Fig. 1 Mean (±SE, n = 62) daily oviposition rate (number of eggs/female/day) of Neoseiulus cucumeris when fed with various food sources. Means capped with different letters are significantly different (Tukey’s HSD: P \ 0.05)
123
Exp Appl Acarol
Fig. 2 Mean (±SE, n = 77) daily oviposition rate (number of eggs/female/day) of Amblyseius swirskii when fed with various food sources. Means capped with different letters are significantly different (Tukey’s HSD: P \ 0.05)
Table 2 Secondary sex ratios (proportion of females) of Neoseiulus cucumeris and Amblyseius swirskii when reared on different diets at 25 °C Thrips larvae
Flour moth eggs
Maize pollen
Cattail pollen
Apple pollen
N. cucumeris
0.74
0.68
0.67
0.68
0.66
A. swirskii
0.73
0.78
0.73
0.7
0.81
feeding being easier when eggs had a flaw on the outer membrane (J.F. Delisle, personal observation). Comparisons of food/prey suitability among laboratory and field studies for a given phytoseiid species are inherently difficult because of differences in prey or predator populations, supplemental food origin and storage conditions, calculation of fitness and population parameters, as well as experimental designs. For example, in a study where pollen from 25 species of plants was tested, apple and cattail pollen generated among the highest oviposition rates for N. cucumeris (van Rijn and Tanigoshi, 1999). These results are similar with what we observed in our study for N. cucumeris. However, when testing the suitability of pollen of 21 plant species for A. swirskii, Goleva and Zebitz (2013) recommended pollen from castor bean (Ricinus communis L.) and maize as supplementary food to be offered to A. swirskii as banker plants in greenhouses. In contrast, A. swirskii did not perform well on maize pollen in our tests. Differences between studies suggest that suitability results are context dependent and that only large differences between life-history estimates should be considered for comparisons among studies. These differences, arising from studies conducted in the laboratory, also suggest that conclusions and recommendations about a specific supplemental food item should be considered with caution when transfered to greenhouse or field situations, where the environment is by far more complex and variable. Maize pollen is the least profitable food item that we tested for both A. swirskii and N. cucumeris with the longest developmental times and the lowest oviposition rates. These results diverge from those of Goleva and Zebitz (2013), as mentioned above, but are consistent with Ranabhat et al. (2014) and Obrist et al. (2005) where maize pollen was a
123
Exp Appl Acarol
less suitable food source for N. cucumeris compared to other pollen sources. Whether the low reproductive rate results from a low rate of feeding, a poor nutritive value of maize pollen or a low efficiency of converting food into eggs remains to be determined. However, during the experimental trial maize pollen appeared to absorb ambient humidity in a much higher proportion than any other food source tested. Within a 12-h period the pollen heap was dampened and, therefore, more difficult to access for mite feeding (J.F. Delisle, personal observation). Maize pollen might therefore lose its nutritive quality faster than other pollen types. Similarly, it has been observed that the nutritive qualities of pollen collected by bees decrease rapidly, likely due to the absorption of air humidity during collection (see van Rijn and Tanigoshi 1999 and references therein). This factor has to be taken into account when supplemental food sources such as pollen are used in greenhouse pest management. We showed that when fed MFM eggs, A. swirskii can develop from egg to adult as fast as on diets of cattail or apple pollen and reach similar oviposition rates. In contrast, for N. cucumeris, development time when fed MFM eggs was similar to development time on diets of maize pollen and thrips larvae, whereas oviposition rate was similar on all diets, except maize pollen. In light of these results, eggs from the MFM could be considered as a dietary supplement in the form of mixed diet with pollen, thereby forming a suitable food source for both phytoseiid species under study. This mixed diet would be particularly useful in situations where predatory bugs such as Orius spp. (Hemiptera: Anthocoridae) are used in a crop in combination with predatory mites, MFM eggs being also a suitable diet for Orius species (Yano et al. 2002). Vantornhout et al. (2004) and Buitenhuis et al. (2010) reported that development of N. cucumeris fed on thrips larvae was slow and variable, and survival to adulthood was low compared to non-prey food diets. This is consistent with our data, the thrips larval treatment being amongst the diets resulting in the longest development time. The high percentages of predatory mite escape (20.8 %) and immature mortality (29.2 %) may in part result from the aggressive defense behavior of the thrips larvae (Janssen et al. 2002; Magalha˜es et al. 2005). Wimmer et al. (2008) reported similar results for development and oviposition by A. swirskii when fed F. occidentalis larvae. Buitenhuis et al. (2010) also found that the development times for A. swirskii and N. cucumeris were greatly decreased if the thrips were killed first before offering them to the predators. Therefore, prey defensive behavior can greatly modulate their overall profitability for natural enemies (Barrette et al. 2008). For phytoseiid mites, the predator–prey size ratio is such that they can only attack first and second thrips instars, with N. cucumeris being able to feed only on first-instar thrips larvae (Bakker and Sabelis 1989; Cloutier and Johnson 1993). Soluble protein content was 8.59 higher in maize pollen than in cattail pollen. These results did not match the intuitive prediction under which the most beneficial food source would contain the highest concentration in protein; proteinaceous foods being key elements for animal reproduction. For instance, protein intake is required for reproduction in phytoseiid mites (Lundgren 2009). When they emerge in spring before animal sources of protein become available, they can rely on pollen, one of very few sources of protein available at this time of year (Chant 1959). Our results suggest that soluble proteins are not a key determinant of pollen nutritional quality for N. cucumeris and A. swirskii. Carbohydrates, lipids, amino acids and other forms of proteins may be critical nutrients that facilitate the sexual maturation of females and ovogenesis (Coll and Guershon 2002; Lundgren 2009). The identification of such key components could lead to the development of a synthetic supplemental food source of high quality for predatory mites.
123
Exp Appl Acarol
Different pollens, MFM eggs and by extension other potential dietary supplements can be used to optimize rearing of phytoseiid mites, as well as their effectiveness as biocontrol agents in greenhouse crops. However, it is important to note that the prey (F. occidentalis) can also consume pollen. Cattail pollen increased the intrinsic rate of increase of F. occidentalis by 23 % compared to no pollen when applied to cucumber leaves (Hulshof et al. 2003). Van Rijn et al. (2002) showed that small amounts (10–15 mg/plant) of cattail pollen when applied biweekly was enough to increase the population level of the predatory mite Iphiseius degenerens (Berlese) and reduce F. occidentalis populations to lower levels than without pollen. This allows for the consideration of a multifaceted approach when it comes to their use in greenhouses. Food sources unsuitable for pests—potentially MFM eggs—could be used to maintain predatory mite populations within the crop, as opposed to pollen which is also available to thrips (Hulshof et al. 2003). Diets for mass rearing of biocontrol agents could also be expanded to include a much wider range of food sources, opening a possibility for the development and the use of synthetic food sources, combining specific nutrients, and that could be stored longer and possess specific nutrients (Wade et al. 2008). Our results confirm that N. cucumeris and A. swirskii are omnivorous, being able to feed on pollen grains and animal food source such as arthropod eggs as well as their targeted pest species, often showing better performance on alternative food sources. Among the food items tested in this study, apple pollen is an easily accessible commercial product, being available online and a suitable supplement for both predator species. Acknowledgments We thank Jose´e Doyon and Claude Beaudoin for technical assistance, Ste´phane Daigle for statistical advice, and two anonymous reviewers for helpful comments and suggestions on the manuscript. This work was funded by the Agriculture and Agri-Food Canada Growing Forward ‘Canadian Ornamental Horticulture Research and Innovation Cluster’ and by the Canada Research Chair in Biological Control to JB.
References Arthurs S, Mckenzie CL, Chen J, Dogramaci M, Brennan M, Houben K, Osborne L (2009) Evaluation of Neoseiulus cucumeris and Amblyseius swirskii (Acari: Phytoseiidae) as biological control agents of chilli thrips, Scirtothrips dorsalis (Thysanoptera: Thripidae) on pepper. Biol Control 49:91–96 Bakker FM, Sabelis MW (1989) How larvae of Thrips tabaci reduce the attack success of Phytoseiid predators. Entomol Exp Appl 50:47–51 Barrette M, Wu GM, Brodeur J, Giraldeau LA, Boivin G (2008) Testing competing measures of profitability for mobile resources. Oecologia 158:757–764 Bonte M, De Clercq P (2008) Development and reproductive fitness of Orius laevigatus (Hemiptera: Anthocoridae) reared on factitious and artificial diets. J Econ Entomol 101:1127–1133 Buitenhuis R, Shipp L, Scott-Dupree C (2010) Intra-guild versus extra-guild prey: effect on predator fitness and preference of Amblyseius swirskii (Athias-Henriot) and Neoseiulus cucumeris (Oudemans) (Acari: Phytoseiidae). Bull Entomol Res 100:167–173 Chant DA (1959) Phytoseiid mites (Acarina: Phytoseiidae). Part I. Bionomics of seven species in southeastern England. Part II. A taxonomic review of the Phytoseiidae, with description of 38 new species. Mem Entomol Soc Canada 91:1–166 Cloutier C, Johnson GS (1993) Interaction between life stages in a phytoseiid predator: western flower thrips prey killed by adults as food for protonymphs of Amblyseius cucumeris. Exp Appl Acarol 17:441–449 Cohen AC, Smith LK (1998) A new concept in artificial diets for Chrysoperla rufilabris: the efficacy of solid diets. Biol Control 13:49–54 Coll M, Guershon M (2002) Omnivory in terrestrial arthropods: mixing plant and prey diets. Annu Rev Entomol 47:267–297 de Almeida AA, Janssen A (2013) Juvenile prey induce antipredator behaviour in adult predators. Exp Appl Acarol 59:275–282
123
Exp Appl Acarol De Clercq P, Bonte M, Van Speybroeck K, Bolckmans K, Deforce K (2005) Development and reproduction of Adalia bipunctata (Coleoptera: Coccinellidae) on eggs of Ephestia kuehniella (Lepidoptera: Phycitidae) and pollen. Pest Manag Sci 61:1129–1132 Faraji F, Janssen A, Sabelis MW (2001) Predatory mites avoid ovipositing near counterattacking prey. Exp Appl Acarol 25:613–623 Flechtmann CHW, McMurtry JA (1992) Studies of cheliceral and deutosternal morphology of some Phytoseiidae (Acari: Mesostigmata) by scanning electron microscopy. Intern J Acarol 18:163–169 Goleva I, Zebitz CPW (2013) Suitability of different pollen as alternative food for the predatory mite Amblyseius swirskii (Acari, Phytoseiidae). Exp Appl Acarol 61:259–283 Hulshof J, Ketoja E, Vanninen I (2003) Life history characteristics of Frankliniella occidentalis on cucumber leaves with and without supplemental food. Entomol Exp Appl 108:19–32 Janssen A, Faraji F, van der Hammen T, Magalha˜es S, Sabelis MW (2002) Interspecific infanticide deters predators. Ecol Lett 5:490–494 Kostiainen TS, Hoy MA (1996) The Phytoseiidae as biological control agents of pest mites and insects: a bibliography. Monograph 17. Florida University, Gainesville Lundgren JC (2009) Relationships of natural enemies and non-prey foods. Springer, Dordrecht Magalha˜es S, Janssen A, Montserrat M, Sabelis MW (2005) Prey attack and predators defend: counterattacking prey trigger parental care in predators. Proc R Soc B 272:1929–1933 Maoz Y, Gal S, Abrahams J, Gan-Mor S, Coll M, Palevsky E (2008) Pollen provisioning enhance Euseius scutalis (Phytoseiidae) populations and improves control of Oligonychus perseae (Tetranychidae). In: Mason PG, Gillespie DR, Vincent C (eds), Proceedings of the 3rd international symposium on biozlogical control of Arthropods. Christchurch, pp 339–346 McMurtry JA, Croft BA (1997) Life-styles of Phytoseiid mites and their roles in biological control. Annu Rev Entomol 42:291–321 McMurtry JA, Rodriguez JG (1987) Nutritional ecology of phytoseiid mites. In: Slansky F, Rodriguez JG (eds) Nutritional ecology of insects, mites, spiders and related invertebrates. Wiley, New York, pp 609–644 McMurtry JA, Scriven GT (1964) Studies on the feeding, reproduction and development of Amblyseius hibisci (Acarina: Phytoseiidae) on various food substances. Ann Entomol Soc Am 57:649–655 Momen FM, El-Laithy AY (2007) Suitability of the flour moth Ephestia kuehniella (Lepidoptera: Pyralidae) for three predatory phytoseiid mites (Acari: Phytoseiidae) in Egypt. Intern J Trop Insect Sci 27:102–107 Nguyen DT, Vangansbeke D, De Clercq P (2014) Artificial and factitious foods support the development and reproduction of the predatory mite Amblyseius swirskii. Exp Appl Acarol 62:181–194 Nomikou M, Sabelis MW, Janssen A (2010) Pollen subsidies promote whitefly control through the numerical response of predatory mites. Biocontrol 55:253–260 Obrist LB, Klein H, Dutton A, Bigler F (2005) Assessing the effects of Bt maize on the predatory mite Neoseiulus cucumeris. Exp Appl Acarol 38:125–139 Ramakers PMJ (1990) Manipulation of phytoseiid thrips predators in the absence of thrips. SROP/WPRS Bull 8:169–172 Ranabhat NB, Goleva I, Zebitz CPW (2014) Life tables of Neoseiulus cucumeris exclusively fed with seven different pollens. Biocontrol 59:195–203 Romeih AHM, El-Saidy EMA, El-Arnaouty SA (2004) Suitability of Ephestia kuehneilla and Corycera cephalonica eggs as alternative preys for rearing predatory mites. Egypt Soc Biol Control Pests 14:101–105 Roulston TH, Cane JH, Buchman SL (2000) What governs protein content of pollen: pollinator preferences, pollen–pistil interactions, or phylogeny? Ecol Monogr 70:617–643 Tanigoshi LK (1981) Advances in the knowledge of the biology of the Phytoseiidae. In: Hoy MA (ed) Recent advances in knowledge of the Phytoseiidae. University of California Press, Berkeley, pp 1–22 Tuovinen T, Lindqvist I (2010) Maintenance of predatory phytoseiid mites for preventive control of strawberry tarsonemid mite Phytonemus pallidus in strawberry plant propagation. Biol Control 54:119–125 van Houten YM, van Stratum P (1995) Control of western flower thrips on sweet pepper in winter with Amblyseius cucumeris (Oudemans) and A. degenerans Berlese. In: Parker BL, Skinner M, Lewis T (eds) Thrips biology and management. Plenum Press, New York, pp 245–248 van Rijn PC, Sabelis MW (2005) Impact of plant-provided food on herbivore–carnivore dynamics. In: Wa¨ckers FL, van Rijn PCJ, Bruin J (eds) Plant-provided food for carnivorous insects: a protective mutualism and its applications. Cambridge University Press, Cambridge, pp 223–266
123
Exp Appl Acarol van Rijn PCJ, Tanigoshi LK (1999) Pollen as food for the predatory mites Iphiseius degenerans and Neoseiulus cucumeris (Acari: Phytoseiidae): dietary range and life history. Exp Appl Acarol 23:785–802 van Rijn PCJ, van Houten YM, Sabelis MW (1999) Pollen improves thrips control with predatory mites. IOBC/WPRS Bull 22:209–212 van Rijn PCJ, van Houten YM, Sabelis MW (2002) How plants benefit from providing food to predators even when it is also edible to herbivores. Ecology 83:2664–2679 Vandekerkhove B, Parmentier L, van Stappen G, Grenier S, Febvay G, Rey M, De Clercq P (2009) Artemia cysts as an alternative food for the predatory bug Macrolophus pygmaeus. J Appl Entomol 133:133–142 Vangansbeke D, Nguyen DT, Audenaert J, Verhoeven R, Gobin B, Tirry L, De Clercq P (2014) Performance of the predatory mite Amblydromalus limonicus on factitious foods. Biocontrol 59:67–77 Vantornhout I, Minnaert HL, Tirry L, De Clercq P (2004) Effect of pollen, natural prey and factitious prey on the development of Iphiseius degenerans. Biocontrol 49:627–644 Wade MR, Zalucki MP, Wratten SD, Robinson KA (2008) Conservation biological control of arthropods using artificial food sprays: current status and future challenges. Biol Control 45:185–199 Wimmer D, Hoffmann D, Schausberger P (2008) Prey suitability of western flower thrips, Frankliniella occidentalis, and onion thrips, Thrips tabaci, for the predatory mite, Amblyseius swirskii. Biocontrol Sci Technol 18:533–542 Yano E, Watanabe K, Yara K (2002) Life history parameters of Orius sauteri (Poppius) (Het., Anthocoridae) reared on Ephestia kuehniella eggs and the minimum amount of the diet for rearing individuals. J Appl Entomol 126:389–394
123
Evaluation of various types of supplemental food for two species of predatory mites, Amblyseius swirskii and Neoseiulus cucumeris (Acari: Phytoseiidae) J. F. Delisle • J. Brodeur • L. Shipp
Received: 28 November 2013 / Accepted: 6 November 2014 Ó Her Majesty the Queen in Right of Canada 2014
Abstract Although phytoseiids are best known as predators of phytophagous mites and other small arthropods, several species can also feed and reproduce on pollen. In laboratory assays, we assessed the profitability of two types of dietary supplements (three pollen species—cattail, maize and apple—and eggs of the Mediterranean flour moth, Ephestia kuehniella) for the two species of predatory mites most commonly used as biocontrol agents in horticulture in Canada, Neoseiulus cucumeris and Amblyseius swirskii. We measured the effects of each diet on phytoseiid fitness parameters (survival, development, sex ratio, fecundity) and, as a means of comparison, when fed larvae of the common targeted pest species, western flower thrips Frankliniella occidentalis. A soluble protein assay was also performed on the alternative food sources as protein content is often linked to high nutritive value according to the literature. All food sources tested were suitable for N. cucumeris and A. swirskii, both species being able to develop from egg to adult. The dietary supplements had a beneficial impact on biological parameters, mostly resulting in shorter development times and higher survival rates when compared to thrips larvae. Amblyseius swirskii exhibited a wider dietary range than N. cucumeris. Overall, flour moth eggs, cattail pollen and apple pollen are food sources of equal quality for A. swirskii, whereas apple and cattail pollen are better when it comes to N. cucumeris. In contrast, maize pollen is a less suitable food source for N. cucumeris and A. swirskii. Soluble protein content results did not match the prediction under which the most beneficial food source would contain the highest concentration in protein.
J. F. Delisle J. Brodeur (&) De´partement de Sciences Biologiques, Institut de Recherche en Biologie Ve´ge´tale, Universite´ de Montre´al, Montreal, QC H1X 2B2, Canada e-mail: [email protected] L. Shipp Agriculture and Agri-Food Canada, Greenhouse and Processing Crops Research Centre, Harrow, ON N0R 1G0, Canada e-mail: [email protected]
123
Exp Appl Acarol
Keywords Alternative food sources Pollen Ephestia kuehniella egg Frankliniella occidentalis Life history parameters Biological control
Introduction Plants can provide non-prey foods to predators of herbivorous arthropods, an adaptation that may facilitate protection against herbivory by increasing the performance of natural enemies (van Rijn et al. 2002; van Rijn and Sabelis 2005; Lundgren 2009). Several phytoseiids, a large family of predatory mites broadly used as biocontrol agents, are mainly described as predators of phytophagous mites and small arthropods. However, many plantinhabiting phytoseiid mites can feed and reproduce on pollen as well (McMurtry and Scriven 1964; Tanigoshi 1981; McMurtry and Croft 1997). Phytoseiid mite species clearly differ in their propensity/capacity to use pollen and their developmental and reproductive responses to different pollen sources can vary considerably (Kostiainen and Hoy 1996; McMurtry and Croft 1997; Goleva and Zebitz 2013; Ranabhat et al. 2014). Pollen serves as a dietary supplement to prey of low quality or when prey are rare or absent (McMurtry and Croft 1997; Tuovinen and Lindqvist 2010). Pollen is also considered as the favorite food source for immature stages of several phytoseiid mites (Vantornhout et al. 2004). Moreover, McMurtry and Rodriguez (1987) compiled a list of phytoseiids that reproduce better on pollen than on prey. In a biological control context, their ability to feed on pollen allows predatory mites to increase survival during periods of prey scarcity and retention in the crop (van Houten and van Stratum 1995). Accordingly, pollen has long been recognized as an important factor in the success of biological control of whiteflies (Nomikou et al. 2010), thrips (Ramakers 1990; van Rijn et al. 1999), and spider mites (McMurtry and Croft 1997; Maoz et al. 2008), although the most successful predators of Tetranychidae do not feed on pollen (e.g., Phytoseiulus persimilis AthiasHenriot). Supplementary food sources other than that derived from plants have also been investigated for predatory mites. These factitious prey include sterilized eggs of the Mediterranean flour moth (MFM), Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) and cysts of the brine shrimp, Artemia franciscana Kellogg (Branchiopoda: Artemiidae) (Romeih et al. 2004; Vantornhout et al. 2004; Momen and El-Laithy 2007; Nguyen et al. 2014; Vangansbeke et al. 2014). These are frequently used as an alternative food source for insect natural enemies alone, as part of a mixed diet or as a factitious host (e.g., Cohen and Smith 1998; De Clercq et al. 2005; Bonte and De Clercq 2008; Vandekerkhove et al. 2009). In this study, we compared the profitability of different types of alternative food sources, vegetable and animal, that have been proven to be amongst the more suitable for phytoseiids: cattail (Typha latifolia L.), apple (Malus domestica L.) and maize (Zea mays L.) pollen, as well as MFM eggs. These food sources have been chosen according to several prerequisites: accessibility of the food source, storage capacity without alteration of the nutritive quality, known beneficial effects on phytoseiid fitness and potential for subsequent agricultural use in greenhouse crops. The life history characteristics of commercially available Amblyseius swirskii Athias-Henriot and Neoseiulus cucumeris (Oudemans) were determined when fed these dietary supplements, as well as western flower thrips first instars [Frankliniella occidentalis (Pergande)], a common targeted pest
123
Exp Appl Acarol
species for both phytoseiid species. In addition, the nutritional quality of each supplemental food source was partly assessed through biochemical analysis of their soluble protein content, which represents the proteins available to the predatory mites according to their feeding behavior (Flechtmann and McMurtry 1992).
Materials and methods Arthropod cultures Colonies of predatory mites were established from individuals obtained from Biobest Canada (Leamington, ON) and maintained in two separate growth chambers at 25 °C, 65–80 % RH and 16L:8D photoperiod. Phytoseiids were reared on individual Lima bean plant stems, infested with two-spotted spider mites (Tetranychus urticae Koch), maintained on a wire mesh in plastic tanks of 50-l capacity (58.4 9 39 9 29.8 cm) filled with water. The roots of the stems were in constant contact with the water while the foliage stayed dry, allowing the mites to proliferate in a healthy environment. The upper edge of each basin was coated with TanglefootÒ glue and placed on a tray filled with water to prevent contamination. A population of western flower thrips, collected from a hibiscus (Hibiscus sp.) greenhouse at the Botanical Garden of Montre´al (Canada), was maintained on potted chrysanthemum plants cv. Butterfield (Planterra, Dorval, QC, Canada) in a growth chamber at 25 °C, 60 % RH and 16L:8D photoperiod. Dietary supplements Eggs of MFM were provided by the Horticulture Research and Development Centre (StJean-sur-Richelieu, QC, Canada). Fresh eggs (\24 h) were killed and sterilized in a freezer (-15 °C for 24 h) and refrigerated (4 °C) for up to 2 weeks before the trials. Cattail pollen was harvested in June 2011 at the Montre´al Botanical Garden, whereas maize pollen (Zea mays L.) was harvested in July 2011 in a maize field at the CE´ROM Grain Research Center (St-Mathieu-de-Beloeil, QC, Canada). Apple pollen (cv. red delicious) was purchased from Firman Pollen (Yakima, WA, USA). The different pollens after collection or receipt were immediately transferred into small vials which were placed in a jar containing a color indicator desiccant agent (DrieriteÒ) and then frozen at -20 °C for long-term storage or refrigerated (4 °C) for up to 2 weeks during the experiments (van Rijn and Tanigoshi 1999). Experimental conditions and treatments The experimental unit was a Lima bean leaf disc (2 cm diameter) placed upside down on WhatmanÒ filter paper saturated with water, inside a Petri dish (4 cm diameter) covered with a lid. The lid contained a small venting hole to keep a suitable humidity level inside the dish. The Petri dishes were placed in a growth chamber at 25 °C, 60–70 % RH and 16L:8D photoperiod. A small piece of brown paper was placed in the center of the leaf disc as a refuge and oviposition site. It also prevented the mites from leaving the leaf disc and drowning, especially N. cucumeris (Arthurs et al. 2009). Individuals were transferred to a new arena every day, containing a fresh leaf disc and food source according to the treatment. The development time of each developmental stage, survival rate to adulthood,
123
Exp Appl Acarol
escape rate (see below), oviposition rate and the secondary sex ratio (proportion of females in the progeny) of A. swirskii and N. cucumeris were determined when fed with alternative food sources or thrips larvae. The ten experimental treatments included: predator ? prey (A. swirskii ? thrips larvae and N. cucumeris ? thrips larvae) and predator ? supplemental food (A. swirskii ? flour moth eggs; A. swirskii ? maize pollen; A. swirskii ? cattail pollen; A. swirskii ? apple pollen; N. cucumeris ? flour moth eggs; N. cucumeris ? maize pollen; N. cucumeris ? cattail pollen and N. cucumeris ? apple pollen). Three repetitions (blocks) were completed over time and at the beginning of each block and for each phytoseiid species, a total of 60 gravid females were collected from the rearing culture and placed on leaves infested by spider mites in Petri dishes. After 12 h, 40 eggs per species were individually transferred to experimental arenas to obtain an initial number of eight eggs per treatment. Three blocks were completed to obtain 24 replicates per treatment. Development time, survival rate and escape rate Every 12 h, phytoseiid eggs were checked for hatching. After hatching, the immature predatory mites were fed ad libitum daily with the dietary supplement according to the treatment [0.05 mg of pollen (following preliminary tests), 10 MFM eggs (following Vantornhout et al. 2004) or 10 first instar thrips (following Arthurs et al. 2009)]. The presence of an exuvium was verified every 12 h, indicating the transition to a new stage (van Rijn and Tanigoshi 1999). Development time of each stage, from egg to adult, was calculated in hours. Death of individuals was set at the mid-point between the last observation alive and the first record of death. The survival rate to adulthood was calculated as well as the escape rate, i.e., when the mites escaped the leaf disc and were drowned or not retrieved. After the experiment, each individual was mounted on a slide and observed under a microscope for sex determination. Oviposition rate and sex ratio Following Momen and El-Laithy (2007), during the last day of the deutonymph stage each female was placed with a male from the rearing colony for 24 h. Each mated female was then fed ad libitum as described previously for each treatment. The duration of the adult pre-oviposition period was determined (time between the third molt, marking the beginning of adulthood, and the first egg laid). Because the rate of oviposition typically reaches a stable level after 3 days (van Rijn and Tanigoshi 1999), eggs laid on days 4 and 5 were counted and removed after each observation interval of 12 h. Those eggs were then placed on an isolated leaf disc in a Petri dish and raised to adulthood on cattail pollen. The adults were then sexed to determine the secondary sex ratio. Cattail pollen was used because it is suitable for both predatory mites, thus avoiding differential mortality of the offspring before sex determination. In the two predator ? prey treatments, we cannot rule out the possibility that some eggs of the predator were killed by thrips larvae. In addition to being phytophagous, all active stages of F. occidentalis have the capacity to feed on eggs of various species of phytoseiids (Faraji et al. 2001; Janssen et al. 2002). However, predatory mites have been shown to display anti-predator behaviour against F. occidentalis to protect mite eggs by depositing them away from the thrips larvae (Magalha˜es et al. 2005; de Almeida and Janssen 2013). Thus, predation of mite eggs by first instars could have occurred, but such a pattern should be reduced to a minimum due to the presence of the
123
Exp Appl Acarol
adult mite, removal of eggs every 12 h, presence of a small refuge for oviposition, and because small and less voracious first instar thrips were used in our tests. Protein assay Soluble protein content of supplemental food items was measured using the Bradford method (Roulston et al. 2000). A standard calibration curve was initially performed with BSA (bovine serum albumin) in concentrations ranging from 0 to 0.02 g/l. To do that, 0.7 g of each dietary supplement was ground and then transferred into a vial containing 2.5 ml of extraction buffer (Tris HCl) (25 mM). The pH was adjusted to 7.5 (cytosolic). The mixture was centrifuged at 1,200–1,500g, supernatant removed and the solution was re-suspended to fill aliquots of 250 ll containing 200 ll of Bradford reagent and volumes ranging from 0 to 50 ll sample. Following incubation for 10 min at room temperature, the proteins were measured by reading the plate at 595 nm. Statistical analysis Due to the nature of the data acquisition of development time for each stage (intervals of 12 h), the distribution presents a modal numeric response and was analyzed using a Kruskal–Wallis test. A non-parametric post hoc comparison was performed with a Sidak correction to control comparison-wise error. Adjusted means for survival rates to adulthood and escape rates were calculated and analyzed with a log-linear analysis of frequency tables. The daily oviposition rates were analyzed using a one-way ANOVA. Model effects included block, treatment and their interaction. Block was set as a random effect. Tukey’s honestly significant difference (HSD) test was performed to determine the differences of least squares to an alpha error threshold of 5 %. The protein content data was compared between supplemental foods using a Kruskal–Wallis one-way test, followed by a nonparametric post hoc comparison with a Sidak correction.
Results Survival rate, escape rate and development time For A. swirskii and N. cucumeris, both sexes were analysed together because there was no significant difference between males and females for each developmental stage (Wilcoxon test, a = 0.05). Both predatory mite species developed to adult stage on every food source and immature survival rate, as well as escape rate, were not different among treatments (Table 1). For all food sources, developmental time of N. cucumeris was similar during the egg and larval stages (Table 1). Similarly, no difference was found among treatments in developmental time of egg, larva and protonymph of A. swirskii. For both species, the effects of the food source were the most pronounced during the protonymph or deutonymphal stages. For N. cucumeris, the shortest development times from egg to adult were observed when fed with cattail and apple pollen. For A. swirskii, the same trend was observed, as the cattail and apple pollen diets, as well as the MFM eggs diet, led to the shortest egg to adult development times.
123
123
1.39 ± 0.17a
95.8a
0a
Pre-oviposition
Survival (%)
Escape (%)
1.17 ± 0.10ab
5.05 ± 0.10ab
Deutonymph
Total
3.4a
100a
1.41 ± 0.17a
4.87 ± 0.17b
1.13 ± 0.10ab
1.29 ± 0.12a
0.55 ± 0.05a
0.57 ± 0.05a
1.43 ± 0.12a
Larvae
Protonymph
1.92 ± 0.08a
12.5a
87.5a
1.90 ± 0.08a
20.8a
Escape (%)
Egg
70.8a
Survival (%)
1.29 ± 0.21b
9.39 ± 0.60a
9.21 ± 0.57a
1.85 ± 0.24ab
Total
Pre-oviposition
4.53 ± 0.57a 2.32 ± 0.32a
3.95 ± 0.55a
2.77 ± 0.29a
Protonymph
Deutonymph
1.97 ± 0.07a 0.53 ± 0.07a
1.97 ± 0.07a
0.53 ± 0.06a
Egg
Larva
1.89 ± 0.07a
13.8a
95.8a
1.88 ± 0.17a
5.41 ± 0.10a
1.47 ± 0.11a
1.38 ± 0.12a
0.60 ± 0.05a
1.96 ± 0.09a
16.7a
79.2a
3.02 ± 0.22a
7.46 ± 0.61a
2.53 ± 0.31a
2.61 ± 0.58ab
0.62 ± 0.07a
2.05 ± 0.07a
3.6a
100a
1.41 ± 0.17a
4.58 ± 0.11b
0.95 ± 0.11b
1.27 ± 0.12a
0.56 ± 0.05a
1.85 ± 0.10a
8.3a
87.5a
1.24 ± 0.19b
5.66 ± 0.63b
1.40 ± 0.33a
1.62 ± 0.58bc
0.52 ± 0.07a
10.7a
100a
1.32 ± 0.18a
4.58 ± 0.11b
1.02 ± 0.10b
1.15 ± 0.12a
0.60 ± 0.05a
1.81 ± 0.09a
0a
95.8a
1.28 ± 0.20b
5.73 ± 0.62b
1.52 ± 0.35a
1.74 ± 0.57c
0.63 ± 0.08a
1.94 ± 0.08a
Apple pollen 6.62
0.16
0.14
v2 = 8.41 1.55
0.82
0.021 0.45 0.14
11.61 v2 = 6.88
\ 0.0001
0.0001
0.024
v2 = 3.69
43.50
22.92
11.29
0.64
0.15
v2 = 6.79 2.50
\ 0.0001
\ 0.0001
\ 0.0001
\ 0.0001
0.63
33.69
60.41
33.31
62.97
2.60
P
Survival rate to adulthood and escape rate are expressed in percentage of adjusted means. For each treatment, an initial number of 24 eggs were used (3 replicates 9 8 individuals). Total number of individuals included in the analysis: n = 120 (N. cucumeris) and 138 (A. swirskii). For each species, means within rows followed by different letters are significantly different (non-parametric post-hoc comparison with a Sidak correction for developmental durations, v2 test for escape and survival rates)
A. swirskii
N. cucumeris
Cattail pollen
H
Maize pollen
Thrips larvae
Flour moth eggs
Statistics (df = 4)
Food source
Table 1 Mean (± SE) duration (days) of Neoseiulus cucumeris and Amblyseius swirskii developmental and pre-oviposition period when reared on different diets at 25 °C
Exp Appl Acarol
Exp Appl Acarol
Oviposition rate and sex ratio The oviposition rate of N. cucumeris females was similar among treatments, except when fed on maize pollen which was at least 8 9 lower than for other food sources (F4,9 = 8.53, P \ 0.001; Fig. 1). For A. swirskii, maize pollen and thrips larvae resulted in the lowest oviposition rates (F4,5 = 5.16, P = 0.002; Fig. 2). For each predatory mite species, secondary sex ratios were similar among treatments (N. cucumeris, v2 = 0.75, P = 0.94; A. swirskii, v2 = 2.16, P = 0.71; both df = 4) (Table 2). Protein content Soluble protein content varied greatly among supplemental food items (F3,3 = 45, P \ 0.0001). Concentrations were the lowest in cattail pollen (4.5 ± 0.38 mg/g), intermediate in apple (26.5 ± 3.57 mg/g) and maize pollen (38.6 ± 0.60 mg/g) and maximum in flour moth eggs (45.6 ± 1.18 mg/g).
Discussion All food sources tested were suitable for N. cucumeris and A. swirskii. Both species were able to develop and reproduce when fed pollen (maize, cattail and apple) or MFM eggs. These food items were more suitable, mostly in terms of immature development, than first instars of the common targeted pest species, F. occidentalis. However, significant differences among food sources and between species were found. Amblyseius swirskii exhibited a wider dietary range than N. cucumeris, being able to develop rapidly when fed most diets, except thrips larvae and maize pollen, the latter resulting in the lowest oviposition rate. Overall, MFM eggs, cattail pollen and apple pollen are food sources of equal quality for A. swirskii, whereas apple and cattail pollen are better when it comes to N. cucumeris. The differences observed between the two species may result from their efficiency to convert food into eggs and their intrinsic capacity to feed on different food items given the morphology of predatory mite mouth appendages (Flechtmann and McMurtry 1992). For example, juvenile stages of N. cucumeris had difficulty to feed on intact MFM eggs,
Fig. 1 Mean (±SE, n = 62) daily oviposition rate (number of eggs/female/day) of Neoseiulus cucumeris when fed with various food sources. Means capped with different letters are significantly different (Tukey’s HSD: P \ 0.05)
123
Exp Appl Acarol
Fig. 2 Mean (±SE, n = 77) daily oviposition rate (number of eggs/female/day) of Amblyseius swirskii when fed with various food sources. Means capped with different letters are significantly different (Tukey’s HSD: P \ 0.05)
Table 2 Secondary sex ratios (proportion of females) of Neoseiulus cucumeris and Amblyseius swirskii when reared on different diets at 25 °C Thrips larvae
Flour moth eggs
Maize pollen
Cattail pollen
Apple pollen
N. cucumeris
0.74
0.68
0.67
0.68
0.66
A. swirskii
0.73
0.78
0.73
0.7
0.81
feeding being easier when eggs had a flaw on the outer membrane (J.F. Delisle, personal observation). Comparisons of food/prey suitability among laboratory and field studies for a given phytoseiid species are inherently difficult because of differences in prey or predator populations, supplemental food origin and storage conditions, calculation of fitness and population parameters, as well as experimental designs. For example, in a study where pollen from 25 species of plants was tested, apple and cattail pollen generated among the highest oviposition rates for N. cucumeris (van Rijn and Tanigoshi, 1999). These results are similar with what we observed in our study for N. cucumeris. However, when testing the suitability of pollen of 21 plant species for A. swirskii, Goleva and Zebitz (2013) recommended pollen from castor bean (Ricinus communis L.) and maize as supplementary food to be offered to A. swirskii as banker plants in greenhouses. In contrast, A. swirskii did not perform well on maize pollen in our tests. Differences between studies suggest that suitability results are context dependent and that only large differences between life-history estimates should be considered for comparisons among studies. These differences, arising from studies conducted in the laboratory, also suggest that conclusions and recommendations about a specific supplemental food item should be considered with caution when transfered to greenhouse or field situations, where the environment is by far more complex and variable. Maize pollen is the least profitable food item that we tested for both A. swirskii and N. cucumeris with the longest developmental times and the lowest oviposition rates. These results diverge from those of Goleva and Zebitz (2013), as mentioned above, but are consistent with Ranabhat et al. (2014) and Obrist et al. (2005) where maize pollen was a
123
Exp Appl Acarol
less suitable food source for N. cucumeris compared to other pollen sources. Whether the low reproductive rate results from a low rate of feeding, a poor nutritive value of maize pollen or a low efficiency of converting food into eggs remains to be determined. However, during the experimental trial maize pollen appeared to absorb ambient humidity in a much higher proportion than any other food source tested. Within a 12-h period the pollen heap was dampened and, therefore, more difficult to access for mite feeding (J.F. Delisle, personal observation). Maize pollen might therefore lose its nutritive quality faster than other pollen types. Similarly, it has been observed that the nutritive qualities of pollen collected by bees decrease rapidly, likely due to the absorption of air humidity during collection (see van Rijn and Tanigoshi 1999 and references therein). This factor has to be taken into account when supplemental food sources such as pollen are used in greenhouse pest management. We showed that when fed MFM eggs, A. swirskii can develop from egg to adult as fast as on diets of cattail or apple pollen and reach similar oviposition rates. In contrast, for N. cucumeris, development time when fed MFM eggs was similar to development time on diets of maize pollen and thrips larvae, whereas oviposition rate was similar on all diets, except maize pollen. In light of these results, eggs from the MFM could be considered as a dietary supplement in the form of mixed diet with pollen, thereby forming a suitable food source for both phytoseiid species under study. This mixed diet would be particularly useful in situations where predatory bugs such as Orius spp. (Hemiptera: Anthocoridae) are used in a crop in combination with predatory mites, MFM eggs being also a suitable diet for Orius species (Yano et al. 2002). Vantornhout et al. (2004) and Buitenhuis et al. (2010) reported that development of N. cucumeris fed on thrips larvae was slow and variable, and survival to adulthood was low compared to non-prey food diets. This is consistent with our data, the thrips larval treatment being amongst the diets resulting in the longest development time. The high percentages of predatory mite escape (20.8 %) and immature mortality (29.2 %) may in part result from the aggressive defense behavior of the thrips larvae (Janssen et al. 2002; Magalha˜es et al. 2005). Wimmer et al. (2008) reported similar results for development and oviposition by A. swirskii when fed F. occidentalis larvae. Buitenhuis et al. (2010) also found that the development times for A. swirskii and N. cucumeris were greatly decreased if the thrips were killed first before offering them to the predators. Therefore, prey defensive behavior can greatly modulate their overall profitability for natural enemies (Barrette et al. 2008). For phytoseiid mites, the predator–prey size ratio is such that they can only attack first and second thrips instars, with N. cucumeris being able to feed only on first-instar thrips larvae (Bakker and Sabelis 1989; Cloutier and Johnson 1993). Soluble protein content was 8.59 higher in maize pollen than in cattail pollen. These results did not match the intuitive prediction under which the most beneficial food source would contain the highest concentration in protein; proteinaceous foods being key elements for animal reproduction. For instance, protein intake is required for reproduction in phytoseiid mites (Lundgren 2009). When they emerge in spring before animal sources of protein become available, they can rely on pollen, one of very few sources of protein available at this time of year (Chant 1959). Our results suggest that soluble proteins are not a key determinant of pollen nutritional quality for N. cucumeris and A. swirskii. Carbohydrates, lipids, amino acids and other forms of proteins may be critical nutrients that facilitate the sexual maturation of females and ovogenesis (Coll and Guershon 2002; Lundgren 2009). The identification of such key components could lead to the development of a synthetic supplemental food source of high quality for predatory mites.
123
Exp Appl Acarol
Different pollens, MFM eggs and by extension other potential dietary supplements can be used to optimize rearing of phytoseiid mites, as well as their effectiveness as biocontrol agents in greenhouse crops. However, it is important to note that the prey (F. occidentalis) can also consume pollen. Cattail pollen increased the intrinsic rate of increase of F. occidentalis by 23 % compared to no pollen when applied to cucumber leaves (Hulshof et al. 2003). Van Rijn et al. (2002) showed that small amounts (10–15 mg/plant) of cattail pollen when applied biweekly was enough to increase the population level of the predatory mite Iphiseius degenerens (Berlese) and reduce F. occidentalis populations to lower levels than without pollen. This allows for the consideration of a multifaceted approach when it comes to their use in greenhouses. Food sources unsuitable for pests—potentially MFM eggs—could be used to maintain predatory mite populations within the crop, as opposed to pollen which is also available to thrips (Hulshof et al. 2003). Diets for mass rearing of biocontrol agents could also be expanded to include a much wider range of food sources, opening a possibility for the development and the use of synthetic food sources, combining specific nutrients, and that could be stored longer and possess specific nutrients (Wade et al. 2008). Our results confirm that N. cucumeris and A. swirskii are omnivorous, being able to feed on pollen grains and animal food source such as arthropod eggs as well as their targeted pest species, often showing better performance on alternative food sources. Among the food items tested in this study, apple pollen is an easily accessible commercial product, being available online and a suitable supplement for both predator species. Acknowledgments We thank Jose´e Doyon and Claude Beaudoin for technical assistance, Ste´phane Daigle for statistical advice, and two anonymous reviewers for helpful comments and suggestions on the manuscript. This work was funded by the Agriculture and Agri-Food Canada Growing Forward ‘Canadian Ornamental Horticulture Research and Innovation Cluster’ and by the Canada Research Chair in Biological Control to JB.
References Arthurs S, Mckenzie CL, Chen J, Dogramaci M, Brennan M, Houben K, Osborne L (2009) Evaluation of Neoseiulus cucumeris and Amblyseius swirskii (Acari: Phytoseiidae) as biological control agents of chilli thrips, Scirtothrips dorsalis (Thysanoptera: Thripidae) on pepper. Biol Control 49:91–96 Bakker FM, Sabelis MW (1989) How larvae of Thrips tabaci reduce the attack success of Phytoseiid predators. Entomol Exp Appl 50:47–51 Barrette M, Wu GM, Brodeur J, Giraldeau LA, Boivin G (2008) Testing competing measures of profitability for mobile resources. Oecologia 158:757–764 Bonte M, De Clercq P (2008) Development and reproductive fitness of Orius laevigatus (Hemiptera: Anthocoridae) reared on factitious and artificial diets. J Econ Entomol 101:1127–1133 Buitenhuis R, Shipp L, Scott-Dupree C (2010) Intra-guild versus extra-guild prey: effect on predator fitness and preference of Amblyseius swirskii (Athias-Henriot) and Neoseiulus cucumeris (Oudemans) (Acari: Phytoseiidae). Bull Entomol Res 100:167–173 Chant DA (1959) Phytoseiid mites (Acarina: Phytoseiidae). Part I. Bionomics of seven species in southeastern England. Part II. A taxonomic review of the Phytoseiidae, with description of 38 new species. Mem Entomol Soc Canada 91:1–166 Cloutier C, Johnson GS (1993) Interaction between life stages in a phytoseiid predator: western flower thrips prey killed by adults as food for protonymphs of Amblyseius cucumeris. Exp Appl Acarol 17:441–449 Cohen AC, Smith LK (1998) A new concept in artificial diets for Chrysoperla rufilabris: the efficacy of solid diets. Biol Control 13:49–54 Coll M, Guershon M (2002) Omnivory in terrestrial arthropods: mixing plant and prey diets. Annu Rev Entomol 47:267–297 de Almeida AA, Janssen A (2013) Juvenile prey induce antipredator behaviour in adult predators. Exp Appl Acarol 59:275–282
123
Exp Appl Acarol De Clercq P, Bonte M, Van Speybroeck K, Bolckmans K, Deforce K (2005) Development and reproduction of Adalia bipunctata (Coleoptera: Coccinellidae) on eggs of Ephestia kuehniella (Lepidoptera: Phycitidae) and pollen. Pest Manag Sci 61:1129–1132 Faraji F, Janssen A, Sabelis MW (2001) Predatory mites avoid ovipositing near counterattacking prey. Exp Appl Acarol 25:613–623 Flechtmann CHW, McMurtry JA (1992) Studies of cheliceral and deutosternal morphology of some Phytoseiidae (Acari: Mesostigmata) by scanning electron microscopy. Intern J Acarol 18:163–169 Goleva I, Zebitz CPW (2013) Suitability of different pollen as alternative food for the predatory mite Amblyseius swirskii (Acari, Phytoseiidae). Exp Appl Acarol 61:259–283 Hulshof J, Ketoja E, Vanninen I (2003) Life history characteristics of Frankliniella occidentalis on cucumber leaves with and without supplemental food. Entomol Exp Appl 108:19–32 Janssen A, Faraji F, van der Hammen T, Magalha˜es S, Sabelis MW (2002) Interspecific infanticide deters predators. Ecol Lett 5:490–494 Kostiainen TS, Hoy MA (1996) The Phytoseiidae as biological control agents of pest mites and insects: a bibliography. Monograph 17. Florida University, Gainesville Lundgren JC (2009) Relationships of natural enemies and non-prey foods. Springer, Dordrecht Magalha˜es S, Janssen A, Montserrat M, Sabelis MW (2005) Prey attack and predators defend: counterattacking prey trigger parental care in predators. Proc R Soc B 272:1929–1933 Maoz Y, Gal S, Abrahams J, Gan-Mor S, Coll M, Palevsky E (2008) Pollen provisioning enhance Euseius scutalis (Phytoseiidae) populations and improves control of Oligonychus perseae (Tetranychidae). In: Mason PG, Gillespie DR, Vincent C (eds), Proceedings of the 3rd international symposium on biozlogical control of Arthropods. Christchurch, pp 339–346 McMurtry JA, Croft BA (1997) Life-styles of Phytoseiid mites and their roles in biological control. Annu Rev Entomol 42:291–321 McMurtry JA, Rodriguez JG (1987) Nutritional ecology of phytoseiid mites. In: Slansky F, Rodriguez JG (eds) Nutritional ecology of insects, mites, spiders and related invertebrates. Wiley, New York, pp 609–644 McMurtry JA, Scriven GT (1964) Studies on the feeding, reproduction and development of Amblyseius hibisci (Acarina: Phytoseiidae) on various food substances. Ann Entomol Soc Am 57:649–655 Momen FM, El-Laithy AY (2007) Suitability of the flour moth Ephestia kuehniella (Lepidoptera: Pyralidae) for three predatory phytoseiid mites (Acari: Phytoseiidae) in Egypt. Intern J Trop Insect Sci 27:102–107 Nguyen DT, Vangansbeke D, De Clercq P (2014) Artificial and factitious foods support the development and reproduction of the predatory mite Amblyseius swirskii. Exp Appl Acarol 62:181–194 Nomikou M, Sabelis MW, Janssen A (2010) Pollen subsidies promote whitefly control through the numerical response of predatory mites. Biocontrol 55:253–260 Obrist LB, Klein H, Dutton A, Bigler F (2005) Assessing the effects of Bt maize on the predatory mite Neoseiulus cucumeris. Exp Appl Acarol 38:125–139 Ramakers PMJ (1990) Manipulation of phytoseiid thrips predators in the absence of thrips. SROP/WPRS Bull 8:169–172 Ranabhat NB, Goleva I, Zebitz CPW (2014) Life tables of Neoseiulus cucumeris exclusively fed with seven different pollens. Biocontrol 59:195–203 Romeih AHM, El-Saidy EMA, El-Arnaouty SA (2004) Suitability of Ephestia kuehneilla and Corycera cephalonica eggs as alternative preys for rearing predatory mites. Egypt Soc Biol Control Pests 14:101–105 Roulston TH, Cane JH, Buchman SL (2000) What governs protein content of pollen: pollinator preferences, pollen–pistil interactions, or phylogeny? Ecol Monogr 70:617–643 Tanigoshi LK (1981) Advances in the knowledge of the biology of the Phytoseiidae. In: Hoy MA (ed) Recent advances in knowledge of the Phytoseiidae. University of California Press, Berkeley, pp 1–22 Tuovinen T, Lindqvist I (2010) Maintenance of predatory phytoseiid mites for preventive control of strawberry tarsonemid mite Phytonemus pallidus in strawberry plant propagation. Biol Control 54:119–125 van Houten YM, van Stratum P (1995) Control of western flower thrips on sweet pepper in winter with Amblyseius cucumeris (Oudemans) and A. degenerans Berlese. In: Parker BL, Skinner M, Lewis T (eds) Thrips biology and management. Plenum Press, New York, pp 245–248 van Rijn PC, Sabelis MW (2005) Impact of plant-provided food on herbivore–carnivore dynamics. In: Wa¨ckers FL, van Rijn PCJ, Bruin J (eds) Plant-provided food for carnivorous insects: a protective mutualism and its applications. Cambridge University Press, Cambridge, pp 223–266
123
Exp Appl Acarol van Rijn PCJ, Tanigoshi LK (1999) Pollen as food for the predatory mites Iphiseius degenerans and Neoseiulus cucumeris (Acari: Phytoseiidae): dietary range and life history. Exp Appl Acarol 23:785–802 van Rijn PCJ, van Houten YM, Sabelis MW (1999) Pollen improves thrips control with predatory mites. IOBC/WPRS Bull 22:209–212 van Rijn PCJ, van Houten YM, Sabelis MW (2002) How plants benefit from providing food to predators even when it is also edible to herbivores. Ecology 83:2664–2679 Vandekerkhove B, Parmentier L, van Stappen G, Grenier S, Febvay G, Rey M, De Clercq P (2009) Artemia cysts as an alternative food for the predatory bug Macrolophus pygmaeus. J Appl Entomol 133:133–142 Vangansbeke D, Nguyen DT, Audenaert J, Verhoeven R, Gobin B, Tirry L, De Clercq P (2014) Performance of the predatory mite Amblydromalus limonicus on factitious foods. Biocontrol 59:67–77 Vantornhout I, Minnaert HL, Tirry L, De Clercq P (2004) Effect of pollen, natural prey and factitious prey on the development of Iphiseius degenerans. Biocontrol 49:627–644 Wade MR, Zalucki MP, Wratten SD, Robinson KA (2008) Conservation biological control of arthropods using artificial food sprays: current status and future challenges. Biol Control 45:185–199 Wimmer D, Hoffmann D, Schausberger P (2008) Prey suitability of western flower thrips, Frankliniella occidentalis, and onion thrips, Thrips tabaci, for the predatory mite, Amblyseius swirskii. Biocontrol Sci Technol 18:533–542 Yano E, Watanabe K, Yara K (2002) Life history parameters of Orius sauteri (Poppius) (Het., Anthocoridae) reared on Ephestia kuehniella eggs and the minimum amount of the diet for rearing individuals. J Appl Entomol 126:389–394
123
