Neotrop Entomol DOI 10.1007/s13744-015-0290-9
PEST MANAGEMENT
Stability of Field-Selected Resistance to Conventional and Newer Chemistry Insecticides in the House Fly, Musca domestica L. (Diptera: Muscidae) N ABBAS1, M IJAZ1, SA SHAD1, H KHAN2 1
Dept of Entomology, Fac of Agricultural Sciences and Technology, Bahauddin Zakariya Univ, Multan, Pakistan Executors Pest Control and Building Cleaning, Dubai, United Arab Emirates
2
Keywords Insecticide resistance, medical pest, resistance management, seasonal variation, sustainable pest management Correspondence N Abbas, Dept of Entomology, Fac of Agricultural Sciences and Technology, Bahauddin Zakariya Univ, Multan, Pakistan; [email protected] Edited by Raúl N Guedes – UFV Received 9 November 2014 and accepted 14 March 2015 * Sociedade Entomológica do Brasil 2015
Abstract The house fly, Musca domestica L. (Diptera: Muscidae), is a pest of livestock and has the ability to develop resistance to different insecticides. We assessed the fluctuations in seasonal stability of house fly resistance to insecticides from poultry facility populations in Pakistan. House fly populations were collected from poultry facilities located at Khanewal, Punjab, Pakistan in three seasons (July, November, and March) to investigate the fluctuations in their resistance to conventional (organophosphate, pyrethroid) and novel chemistry (spinosyn, oxadiazine, neonicotinoid) insecticides. Laboratory bioassays were performed using the feeding method of mixing insecticide concentrations with 20% sugar solutions, and cotton pads dipped in insecticide solutions were provided to tested adult flies. Bioassay results showed that all house fly populations had varying degrees of susceptibility to tested insecticides. Comparisons between populations at different seasons showed a significant fluctuation in susceptibility to organophosphate, pyrethroid, spinosyn, oxadiazine, and neonicotinoid insecticides. Highest resistant levels were found for organophosphate when compared with other tested insecticides. The resistance to conventional insecticides decreased significantly in March compared with July and November, while resistance to oxadiazine and avermectins decreased significantly in November. However, resistance to spinosad and imidacloprid remained stable throughout the seasons. All conventional and novel chemistry insecticides were significantly correlated with each other in all tested seasons except nitenpyram/lambda-cyhalothrin and nitenpyram/ imidacloprid. Our data suggests that the variation in house fly resistance among seasons could be due to fitness costs or to the cessation of selection pressure in the off-season. These results have significant implications for the use of insecticides in house fly management.
Introduction The house fly, Musca domestica L. (Diptera: Muscidae), is a serious pest of livestock and humans (Scott et al 2000, Kaufman et al 2001, Deacutis et al 2006), causing health and environmental problems by vectoring diseases from animals to man and animal to animal. House flies reproduce on
all eatable materials and wastes and are a known vector of more than 100 disease pathogens, including bacteria, protozoa, helminths, and viruses (Förster et al 2007, Acevedo et al 2009, Khan et al 2012, Abbas et al 2014a). Outbreaks of diarrheal diseases are associated with seasonal abundance of house flies in urban and rural settings of many countries, including Pakistan (Graczyk et al 2001, Khan & Akram 2014).
Abbas et al
The house fly is also a vector of the bird flu virus, an avian influenza that is a serious problem in poultry throughout the world (Barin et al 2010, Wanaratana et al 2011). Millions of domestic poultry flocks are affected by the avian influenza virus which has caused more than 150 deaths of humans globally (Otte et al 2007). In areas of poultry farming, like Punjab Pakistan, uncovered poultry manure provides an ideal condition for growth and reproduction of house flies. Highdensity populations of flies irritate workers, stress hens, and reduce the aesthetic value of livestock, leading to economic losses (Acevedo et al 2009, Abbas et al 2014a). Synthetic insecticides, including organophosphate, carbamate, pyrethroid, and novel chemistry classes, have been used to control the house fly worldwide, including Pakistan. Judicious and appropriate insecticide applications are helpful in conditions where high densities of the house fly are associated with avian influenza in poultry (Nielsen et al 2011, Wanaratana et al 2011) and diarrhea in humans (Chavasse et al 1999, Khan & Akram 2014), but season-specific use of insecticides is required. However, inappropriate chemical use and poultry manure stored in open places could result in the development of resistance to insecticides by house flies. These factors may be responsible for avian influenza and diarrhea cases in poultry and humans, respectively, particularly in developing countries. This resistance development is also promoted by a number of biological traits such as adaptability to different environments, high fecundity, a short developmental time, and cross-resistance (Kaufman et al 2010a, Khan et al 2013b). Resistance to all chemical classes is common in house flies worldwide (Scott et al 2000, Acevedo et al 2009, Kaufman et al 2010b, Khan et al 2013a,b, 2014a, Abbas et al 2014a,b). The determination of the stability of insecticide resistance has practical implications in developing effective resistance management strategies (Khan et al 2014b, Afzal et al 2015). The removal of insecticides from spray schedules may bring the resistance level down if resistance is unstable, and consequently, the efficacy of an insecticide can be extended. A decrease in resistance has been reported for insecticideselected insect populations in the field and laboratory (Carriére & Tabashnik 2001). Effective resistance management programs depend upon different mechanisms of resistance and factors that enhance susceptibility recovery. A reduction in resistance levels may be due to the negative effects of resistance genes on fitness components without insecticide selection pressure. When insecticide exposure is not a constant factor, the susceptibility of resistant individuals may change in the absence of selection pressure under laboratory conditions (Roush 1993, Kristensen et al 2000, Abbas et al 2014b). We assessed the fluctuations in insecticide resistance of house fly populations from Khanewal, Punjab, Pakistan. House fly peak densities start in March and continue until
August. Therefore, house fly populations were collected in different seasons (late summer, early winter, and early spring) to assess the variation in susceptibility to pyrethroids (cypermethrin, lambda-cyhalothrin), organophosphate (chlorpyrifos), neonicotinoids (imidacloprid, acetamiprid, nitenpyram), spinosyn (spinosad), oxadiazine (indoxacarb), and avermectins (abamectin and emamectin benzoate). The results of this study can have a significant role in developing strategies for house fly resistance management through the selection of the most appropriate insecticide to deal with the unstable nature of resistance in specific months of the year for the management of house flies.
Material and Methods Insect rearing About 200 adult house flies were collected from a poultry farm located at Khanewal (32°4′50N, 73°38′10E) in three different seasons denoted by March, July, and November with a sweep net. Adult flies were kept in meshed plastic jars (34× 17 cm) and fed on a mixture of sugar and powdered milk (1:1 w/w). Cotton wicks soaked with water were provided in a Petri dish in order to supplement moisture requirements. Larvae were reared on an artificial diet comprising powdered milk, sugar, yeast, grass meal, and wheat bran (1.5:1.5:5:5:20 w/w) and 65 mL of water (Abbas et al 2014a). The colony was maintained under laboratory conditions according to Abbas et al (2014a). The susceptible strain was collected from an insecticide-free area (Multan) and maintained in the laboratory without exposure to insecticides. Insecticides Commercial formulated insecticides were used for bioassays including conventional: chlorpyrifos (Lorsban® 40EC, Arysta Life Sciences), cypermethrin (Arrivo® 10EC, FMC), and lambda-cyhalothrin (Karate® 2.5EC, Syngenta); and newer chemistries: spinosad (Tracer® 240SC, Arysta Life Sciences), indoxacarb (Steward® 150SC, Arysta Life Sciences), abamectin (Alarm® 1.8EC, DJC), emamectin benzoate (Proclaim® 019EC, Syngenta), acetamiprid (Mospilan® 70WP, Arysta Life Sciences), imidacloprid (Confidor® 20SL, Bayer Crop Science), and nitenpyram (Paranol® 10EC, Kenzo Agro Chemicals). Toxicological bioassays The toxicities of the tested insecticides were assessed by using a feeding bioassay (Kaufman et al 2006). Ten 2–3day-old male and female flies were provided with a cotton wick (3 cm) soaked in 20% sugar solution plus insecticide and
Stability of Field Resistance to Selected Insecticides in House Flies
kept in plastic jars (14×9 cm) (Abbas et al 2014b). Five concentrations were prepared as serial dilutions for each insecticide, and each concentration was replicated three times (10 flies/replicate). The range of concentrations was 8–128 μg· mL−1 for organophosphate, pyrethroid, and neonicotinoid; 0.125–2 μg·mL−1 for avermectins; and 1–16 μg·mL−1 for spinosyn and oxadiazine in all tested strains. Cotton wicks soaked in 20% sugar solution without insecticide were provided to control flies (3 replicates of 10 flies). Cotton wicks were hydrated (without sugar solution) after 24 and 48 h to avoid wick drying (Kaufman et al 2006). All flies were kept under laboratory conditions as earlier described. Mortality data was assessed 48 h after exposure to conventional and 72 h after exposure to newer chemistry insecticides. Ataxic flies were considered as dead (Abbas et al 2014a). Data analysis Concentration response data were analyzed by probit analysis (Finney 1971) with POLO software (Software 2005) to determine LC50 values, their 95% confidence intervals (CI), slopes, and their standard errors. Control mortality was corrected by the formula of Abbott (1925), whenever required. Resistance ratio (RR) and its 95% CI were calculated by dividing the LC50 value and its 95% CI of test strains by the LC50 of the susceptible strain (Ban et al 2012). LC50 values were not considered significantly different when their 95% CI overlapped. The resistance ratio was considered significant if the 95% CI did not include the value of 1 (Robertson & Preisler 1992). Variation in resistance per month (R) was estimated with the following formula: R ¼ logðfinal LC50 Þ−log ðinitial LC50 Þ=n In the above equation, n indicates the months between two collections. Positive and negative values for R indicate the increase and decrease in resistance, respectively. Coefficient of correlation of mortality responses to insecticides were used to calculate the coefficient of determination by taking square of the coefficient of correlation of responses between any of two tested insecticides (Sayyed et al 2005). LC50 values were not considered significantly different when their 95% CI overlapped (Robertson & Preisler 1992).
Results Toxicity of insecticides to a house fly-susceptible strain The susceptible strain of the house fly was more susceptible to the newer chemistry insecticides. Abamectin, indoxacarb, emamectin benzoate, and spinosad were more toxic compared
with other tested insecticides. Chlorpyrifos, lambda-cyhalothrin, cypermethrin, and nitenpyram were equally toxic. Imidacloprid and acetamiprid were less toxic (Table 1). The LC50 values of spinosad, indoxacarb, abamectin, and emamectin benzoate were significantly lower compared with other insecticides tested except chlorpyrifos (95% CI did not overlap). There was no significant difference in LC50 values of cypermethrin, lambdacyhalothrin, acetamiprid, and nitenpyram (95% CI overlapped). The LC50 of imidacloprid was higher compared with all other tested insecticides (95% CI did not overlap) (Table 1). Stability of resistance to conventional insecticides Resistance to conventional insecticides in poultry facilitycollected strains varied significantly with the season (Table 2). In populations collected at 3-month intervals, the resistance level for chlorpyrifos decreased significantly in March compared with July and November but increased slightly in November compared with the strain collected in July. The resistance to cypermethrin and lambda-cyhalothrin decreased significantly in March compared with July and November. The declined rate of resistance to cypermethrin (−0.2) and lambda-cyhalothrin (−0.3) was similar for the strain collected in March. Stability of resistance to newer chemistry insecticides Resistance to newer chemistry insecticides varied significantly with the season in the poultry facility-collected house fly strains (Table 2). The resistance to spinosad remained stable throughout the season in which strains were collected. The resistance to indoxacarb, abamectin, and emamectin benzoate decreased significantly in November compared with the strains collected in July and March. However, resistance remained stable for the strains collected in July and March. Table 1 Toxicity of insecticides to the susceptible strain of Musca domestica. Insecticide
LC50 (95% CI) (μg·mL−1)
Slope (±SE)
Chlorpyrifos Cypermethrin Lambda-cyhalothrin Spinosad Indoxacarb Abamectin Emamectin benzoate Imidacloprid
1.0 (0.5–1.5) 2.1 (1.6–2.6) 1.9 (1.4–2.5) 0.4 (0.3–0.6) 0.4 (0.2–0.5) 0.2 (0.1–0.4) 0.4 (0.3–0.6) 6.7 (3.8–19)
1.8±0.4 2.6±0.4 2.1±0.3 1.7±0.3 1.6±0.3 1.3±0.3 1.5±0.3 0.9±0.3
Acetamiprid Nitenpyram
3.2 (2.4–4.2) 2.5 (1.8–3.3)
2.6±0.4 2.0±0.3
Number of adult flies tested including controls was 180. CI confidence intervals.
Abbas et al Table 2
Seasonal variation in Musca domestica resistance to different insecticides.
Insecticide
Chemical family
Season
LC50 (95% CI) (μg·mL−1)
Slope
RR (95% CI)a
Rb
Chlorpyrifos
Organophosphate
Cypermethrin
Pyrethroid
July November March July November March July November March July November March July November March July November
48 (31–72) 74 (54–114) 16 (9.9–23) 31 (23–41) 25 (19–34) 8.7 (4.9–13) 66 (49–91) 63 (41–122) 6.7 (1.9–11) 2.9 (1.7–4.4) 3.3 (1.6–6.1) 0.9 (0.01–2.1) 3.5 (2.5–4.8) 1.1 (0.2–2) 6.6 (4.1–10) 0.5 (0.3–0.7) 0.1 (0.04–0.2)
2.1±0.5 1.8±0.3 1.9±0.4 2.6±0.4 2.1±0.3 1.6±0.4 2.2±0.4 2.2±0.3 1.9±0.5 1.5±0.3 2.2±0.3 0.9±0.3 2.2±0.4 0.9±0.3 3.4±1.3 2.1±0.4
48 (31–72) 74 (54–114) 16 (9.9–23) 15 (11–20) 12 (9–16) 4 (2–6) 34 (26–48) 32 (22–64) 3 (1–6) 7.3 (4.3–11) 8.3 (4–15) 2.3 (0.03–5.3) 10 (6.3–12) 2.8 (0.5–5) 19 (10–25) 2.5 (1.5–3.5)
– 0.1 −0.2 – −0.03 −0.2 – −0.01 −0.3 – 0.02 −0.2 – −0.2 0.1 –
1.3±0.3
0.5 (0.2–1)
−0.2
March July November March July November March July November March July November March
0.5 (0.3–0.7) 0.8 (0.5–1.1) 0.1 (0.03–0.2) 1.6 (0.9–9) 16 (11–21) 17 (10–25) 16 (4.6–28) 31 (21–55) 79 (57–225) 14 (6.2–20) 8 (5.4–11) 32 (16–65) 14 (8.8–20)
1.6±0.3 2.7±0.6 1.0±0.3 1.2±0.4 2.2±0.4 1.4±0.3 1.2±0.4 1.7±0.4 1.9±0.5 1.6±0.4 2.4±0.4 1.8±0.3 1.7±0.3
2.5 (1.5–3.5) 4 (1.3–2.8) 0.3 (0.1–0.5) 4 (2.3–23) 2.4 (1.6–3.1) 2.5 (1.5–3.7) 2.4 (0.7–4.2) 10 (6.6–17) 25 (18–70) 4.4 (1.9–6.3) 3.2 (2.2–4.4) 13 (6.4–26) 5.6 (3.5–8)
0.00 – −0.3 0.1 – 0.01 −0.01 – 0.1 −0.1 – 0.2 0.1
Lambda-cyhalothrin
Spinosad
Spinosyn
Indoxacarb
Oxadiazine
Abamectin
Avermectin
Emamectin benzoate
Imidacloprid
Neonicotinoid
Acetamiprid
Nitenpyram
Number of adult flies tested including controls was 180. a
Resistance ratio calculated as LC50 of field population/LC50 of susceptible population.
b
Rate of decrease of resistance.
The declined rate of resistance against indoxacarb (−0.2), abamectin (−0.2), and emamectin benzoate (−0.3) was similar for the strain collected in November. The resistance to imidacloprid remained stable throughout the season in which strains were collected. However, the resistance to acetamiprid and nitenpyram increased significantly in November compared with the strain collected in July and March. The resistance to acetamiprid and nitenpyram did not decrease significantly in July compared with March.
Correlation in insecticides All conventional and newer chemistry insecticides depicted significant correlations with each other in all tested seasons
except nitenpyram/lambda-cyhalothrin and nitenpyram/ imidacloprid, which showed a non-significant correlation in the population collected in July. Similarly, acetamiprid/ cypermethrin, acetamiprid/lambda-cyhalothrin, and nitenpyram/acetamiprid showed non-significant correlation in the population collected in November (Table 3).
Coefficient of determination The coefficient of determination for cypermethrin/ chlorpyrifos decreased between July and November while it increased between November and March. The coefficient of determination for lambda-cyhalothrin/chlorpyrifos and lambda-cyhalothrin/cypermethrin increased between July
Stability of Field Resistance to Selected Insecticides in House Flies Table 3
Correlations in mortality to insecticides in different seasons for different populations of Musca domestica.
March Cypermethrin Lambda-cyhalothrin Acetamiprid Imidacloprid Nitenpyram July Cypermethrin Lambda-cyhalothrin Acetamiprid Imidacloprid Nitenpyram November Cypermethrin Lambda-cyhalothrin Acetamiprid Imidacloprid Nitenpyram
Chlorpyrifos
Cypermethrin
Lambda-cyhalothrin
Acetamiprid
Imidacloprid
0.99** 0.97** 0.97** 0.80** 0.96**
0.93* 0.97** 0.99*** 0.99**
0.94* 0.92* 0.90*
0.99** 0.93*
0.98**
0.98** 0.98** 0.98** 0.99*** 0.90*
0.96** 0.97** 0.97** 0.95*
0.99*** 0.99*** 0.84 ns
0.98** 0.88*
0.85 ns
0.97** 0.98** 0.93* 0.98**
0.99*** 0.85 ns 0.98**
0.85 ns 0.99***
0.89*
0.95**
0.94*
0.98**
0.83 ns
0.98**
ns not significant. *P≤0.05; **P≤0.01; ***P≤0.001.
and November while it decreased between November and March (Fig 1a). The coefficient of determination of acetamiprid/chlorpyrifos or cypermethrin or lambdacyhalothrin decreased between July and November but increased between November and March (Fig 1b). The coefficient of determination for imidacloprid/ acetamiprid decreased between July and November and increased between November and March. The coefficient of determination increased for imidacloprid/cypermethrin while it decreased for imidacloprid/chlorpyrifos from July to March. The coefficient of determination for imidacloprid/ lambda-cyhalothrin remained stable between July and November but decreased between November and March (Fig 1c). The coefficient of determination for nitenpyram/ chlorpyrifos increased from July to March. The coefficient of determination for nitenpyram/cypermethrin decreased between July and November while it increased between November and March. In contrast, the coefficient of determination for nitenpyram/lambda-cyhalothrin increased between July and November and decreased between November and March. The coefficient of determination for nitenpyram/acetamiprid decreased between July and November but increased between November and March. The coefficient of determination for nitenpyram/ imidacloprid increased between July and November and remained stable between November and March (Fig 1d).
Discussion Organic insecticides are the major alternative available for house fly control at livestock farms. However, the development of house fly resistance to insecticides slows down the effectiveness of new preparations, making quite difficult the selection of the most effective insecticides (Khan et al 2013a). The use of insecticides with long residual action in close vicinities of productive areas exerts a strong selection pressure that increases resistance development (Scott et al 2000). Conventional (pyrethroids and organophosphates) and newer chemistries (spinosyn, oxadiazine, and avermectin) are commonly used for the management of house fly in livestock farms worldwide, including Pakistan. The fluctuations in insecticide resistance patterns observed in our study suggest that the susceptibility decreased during July and November for chlorpyrifos, cypermethrin, lambdacyhalothrin, spinosad, and acetamiprid. Susceptibility decreased in the months of July and March for indoxacarb, abamectin, and emamectin benzoate, but increased for nitenpyram. Resistance to imidacloprid remained stable throughout the months in which strains were collected. For some insecticides, resistance increased in late summer to early winter and decreased in early spring. In contrast, resistance increased in early spring and late summer and decreased in early winter for some insecticides. This might be due to resistance genes, unmeasured fitness costs,
Abbas et al
B
Coefficient of determinaon
A
1.20
1.00 0.98 0.96 0.94 0.92 0.90 0.88 0.86 0.84 0.82 0.80
1.00 0.80 0.60 0.40
Lambda-Chlor
0.20
Lambda-Cyper July
Coefficient of determinaon
Cyper-Chlor
November Collecon date
0.00 July
March
C
D
1.20
1.20
1.00
1.00
0.80
0.80
0.60
0.60
Imida-Chlor Imida-Cyper Imida-Lambda Imida-Aceta
0.40 0.20
Aceta-Chlor Aceta-Cyper Aceta-Lambda
0.20 0.00
July
November Collecon date
March
March
Niten-Chlor Niten-Cyper Niten-Lambda Niten-Aceta Niten-Imida
0.40
0.00
November Collecon date
July
November Collecon date
March
Fig 1 Variations in coefficients of determination of different combinations of a cypermethrin, lambda-cyhalothrin, and chlorpyrifos; b of acetamiprid, chlorpyrifos, cypermethrin, and lambda-cyhalothrin; c of imidacloprid, chlorpyrifos, cypermethrin, and lambda-cyhalothrin; and d of nitenpyram, chlorpyrifos, cypermethrin, lambda-cyhalothrin, acetamiprid, and imidacloprid from July to March for different populations of Musca domestica.
hybridization of susceptible individuals, and the selection pressure of different insecticides in poultry farms. The low level of resistance to some insecticides during a certain period of the year is due to the cessation of insecticide use in the off-season. In this study, resistance to conventional and newer chemistry insecticides significantly varied from season to season in M. domestica. The highest use of insecticides occurs from March to August because of the high population of the house fly in these months. It is expected that an increase in resistance occurs during these months because resistant adults would have mated and oviposited. Resistance to most of the newer chemistry insecticides tested increased in July and March. However, resistance to organophosphates and pyrethroids decreased in March. Previously, the fluctuation in resistance to different insecticides has been observed in insect pests like Plutella xylostella L. (Sayyed et al 2005). The fluctuation of resistance in our study might be due to the decreased usage of organophosphate and pyrethroid insecticides in March, but increased resistance for newer chemistry insecticides is due to their frequent applications for house fly control. Higher resistance to pyrethroids and organophosphates in November may be because of cross-resistance between these insecticides. Cross-resistance between pyrethroids and organophosphates could be due to the involvement of esterases (Ahmad et al 2007). The house
fly might have developed resistance through different mechanisms, but if the resistance is completely or incompletely dominant, then a minimum of two different mechanisms of resistance can occur (Rahardja & Whalon 1995, Sayyed et al 2005). Previously, an autosomal, incompletely dominant resistance and also the involvement of glutathione-S-transferase, esterase, and microsomal monooxygenase esterase mechanism of pyrethroid resistance were reported for the house fly (Abbas et al 2014b). The variation in resistance could also be due to the involvement of fitness costs in the absence of selection pressure from insecticides. Selection pressure with isolan (1-isopropyl-3-methyl-5-pyrazolyl dimethyl carbamate) led to the development of a relatively stable resistant phenotype in this house fly strain, suggesting fitness costs are not involved. In contrast, selection pressure with misopropylphenyl methyl carbamate on the house fly strain produced an unstable phenotype, suggesting high fitness costs are involved (Georghiou 1964). In a previous experiment, a house fly strain collected from the Multan region showed a dose-dependent incomplete dominance of resistance to lambda-cyhalothrin that remained unstable in the absence of selection pressure, which may reveal a high fitness cost (Abbas et al 2014b). The results of our study may have important implications for house fly resistance management to pyrethroids and organophosphates.
Stability of Field Resistance to Selected Insecticides in House Flies
A simple alternate insecticide use strategy can be easily practiced in tropical and sub-tropical climatic conditions. Applications of insecticides at a specific season when susceptibility is higher can lead to a greater change in frequency of resistance alleles. Therefore, alternate use of insecticides belonging to different groups should be recommended and inhibit the application of insecticides of the same group repeatedly. To prevent diarrheal and avian influenza epidemics, house fly outbreaks should be controlled by using appropriate insecticides suited to the prevailing environmental situations. Moreover, alternate use of the most effective insecticides in the most suitable season of the year will reduce selection pressure and ultimately delay the development of insecticide resistance (Abbas et al 2014a, Khan & Akram 2014). The house fly collected from Khanewal showed high susceptibility to spinosad, indoxacarb, abamectin, and emamectin benzoate, so these compounds could be used for this strategy. Poultry farmers have major problems with insecticide use for the management of poultry pests in Pakistan. Inappropriate chemical use at incorrect doses, bad spray methods, and schedule are common. Moreover, adulterated chemical formulations and poor extension services are of significant importance. If the earlier mentioned problems are addressed in a proper manner and farmers are trained for proper use of insecticides and motivated to implement newly developed strategies and techniques, then these problems can be solved in the future. On the basis of our data, we recommend that chlorpyrifos, lambdacyhalothrin, cypermethrin, spinosad, and acetamiprid should be used in March, while indoxacarb, abamectin, and emamectin benzoate in November and nitenpyram in July for house fly control. Acknowledgments The authors are highly grateful to Prof. Dr. Gerald Wilde, Kansas State University, USA for the critical review of manuscript to improve English language.
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biological parameters of cotton mealybug, Phenacoccus solenopsis (Homoptera: Pseudococcidae), in Pakistan. Pest Manag Sci 71:151–158 Ahmad M, Sayyed AH, Crickmore N, Saleem MA (2007) Genetics and mechanism of resistance to deltamethrin in a field population of Spodoptera litura (Lepidoptera: Noctuidae). Pest Manag Sci 63: 1002–1010 Ban L, Zhang S, Huang Z, He Y, Peng Y, Gao C (2012) Resistance monitoring and assessment of resistance risk to pymetrozine in Laodelphax striatellus (Hemiptera: Delphacidae). J Econ Entomol 105:2129–2135 Barin A, Arabkhazaeli F, Rahbari S, Madani S (2010) The housefly, Musca domestica, as a possible mechanical vector of Newcastle disease virus in the laboratory and field. Med Vet Entomol 24:88–90 Carriére Y, Tabashnik B (2001) Reversing insect adaptation to transgenic insecticidal plants. Proc R Soc Lond Ser B Biol Sci 268:1475–1480 Chavasse D, Shier R, Murphy O, Huttly S, Cousens S, Akhtar T (1999) Impact of fly control on childhood diarrhoea in Pakistan: communityrandomised trial. Lancet 353:22–25 Deacutis JM, Leichter CA, Gerry AC, Rutz DA, Watson WD, Geden CJ, Scott JG (2006) Susceptibility of field collected house flies to spinosad before and after a season of use. J Agric Urban Entomol 23:105–110 Finney D (1971) A statistical treatment of the sigmoid response curve. In: Probit analysis, 3rd edn. Cambridge University Press, London, p 333 Förster M, Klimpel S, Mehlhorn H, Sievert K, Messler S, Pfeffer K (2007) Pilot study on synanthropic flies (e.g. Musca, Sarcophaga, Calliphora, Fannia, Lucilia, Stomoxys) as vectors of pathogenic microorganisms. Parasitol Res 101:243–246 Georghiou G (1964) The stability of resistance to carbamate insecticides in the housefly after cessation of selection pressure. Bull World Health Organ 30:85–90 Graczyk TK, Knight R, Gilman RH, Cranfield MR (2001) The role of nonbiting flies in the epidemiology of human infectious diseases. Microbes Infect 3:231–235 Kaufman PE, Scott JG, Rutz DA (2001) Monitoring insecticide resistance in house flies (Diptera: Muscidae) from New York dairies. Pest Manag Sci 57:514–521 Kaufman PE, Gerry AC, Rutz DA, Scott JG (2006) Monitoring susceptibility of house flies (Musca domestica L.) in the United States to imidacloprid. J Agric Urban Entomol 23:195–200 Kaufman PE, Nunez SC, Geden CJ, Scharf ME (2010a) Selection for resistance to imidacloprid in the house fly (Diptera: Muscidae). J Econ Entomol 103:1937–1942 Kaufman PE, Nunez SC, Mann RS, Geden CJ, Scharf ME (2010b) Nicotinoid and pyrethroid insecticide resistance in houseflies (Diptera: Muscidae) collected from Florida dairies. Pest Manag Sci 66:290–294 Khan HAA, Akram W (2014) The effect of temperature on the toxicity of insecticides against Musca domestica L.: implications for the effective management of diarrhea. PLoS One 9:e95636 Khan HAA, Shad SA, Akram W (2012) Effect of livestock manures on the fitness of house fly, Musca domestica L. (Diptera: Muscidae). Parasitol Res 111:1165–1171 Khan HAA, Akram W, Shad SA (2013a) Resistance to conventional insecticides in Pakistani populations of Musca domestica L. (Diptera: Muscidae): a potential ectoparasite of dairy animals. Ecotoxicology 22:522–527 Khan HAA, Shad SA, Akram W (2013b) Resistance to new chemical insecticides in the house fly, Musca domestica L., from dairies in Punjab, Pakistan. Parasitol Res 112:2049–2054 Khan H, Abbas N, Shad SA, Afzal MBS (2014a) Genetics and realized heritability of resistance to imidacloprid in a poultry population of house fly, Musca domestica L. (Diptera: Muscidae) from Pakistan. Pestic Biochem Physiol 114:38–43 Khan HAA, Akram W, Shad SA (2014b) Genetics, cross-resistance and mechanism of resistance to spinosad in a field strain of Musca domestica L. (Diptera: Muscidae). Acta Trop 130:148–154
Abbas et al Kristensen M, Knorr M, Spencer AG, Jespersen JB (2000) Selection and reversion of azamethiphos-resistance in a field population of the housefly Musca domestica (Diptera: Muscidae), and the underlying biochemical mechanisms. J Econ Entomol 93:1788–1795 Nielsen AA, Skovgard H, Stockmarr A, Handberg KJ, Jorgensen PH (2011) Persistence of low-pathogenic avian influenza H5N7 and H7N1 subtypes in house flies (Diptera: Muscidae). J Med Entomol 48:608–614 Otte J, Pfeiffer D, Tiensin T, Price L, Silbergeld E (2007) Highly pathogenic avian influenza risk, biosecurity and smallholder adversity. Livest Res Rural Dev 19:102 Rahardja U, Whalon ME (1995) Inheritance of resistance to Bacillus thuringiensis subsp. tenebrionis CryIIIA delta-endotoxin in Colorado potato beetle (Coleoptera: Chrysomelidae). J Econ Entomol 88:21–26
Robertson J, Preisler H (1992) Pesticide bioassays with arthropods. CRC, Boca Raton Roush R (1993) Occurrence, genetics and management of insecticide resistance. Parasitol Today 9:174–179 Sayyed A, Attique M, Khaliq A (2005) Stability of field‐selected resistance to insecticides in Plutella xylostella (Lep., Plutellidae) from Pakistan. J Appl Entomol 129:542–547 Scott JG, Alefantis TG, Kaufman PE, Rutz DA (2000) Insecticide resistance in house flies from caged-layer poultry facilities. Pest Manag Sci 56:147–153 Software L (2005) POLO for Windows. LeOra Software, Petaluma Wanaratana S, Panyim S, Pakpinyo S (2011) The potential of house flies to act as a vector of avian influenza subtype H5N1 under experimental conditions. Med Vet Entomol 25:58–63
PEST MANAGEMENT
Stability of Field-Selected Resistance to Conventional and Newer Chemistry Insecticides in the House Fly, Musca domestica L. (Diptera: Muscidae) N ABBAS1, M IJAZ1, SA SHAD1, H KHAN2 1
Dept of Entomology, Fac of Agricultural Sciences and Technology, Bahauddin Zakariya Univ, Multan, Pakistan Executors Pest Control and Building Cleaning, Dubai, United Arab Emirates
2
Keywords Insecticide resistance, medical pest, resistance management, seasonal variation, sustainable pest management Correspondence N Abbas, Dept of Entomology, Fac of Agricultural Sciences and Technology, Bahauddin Zakariya Univ, Multan, Pakistan; [email protected] Edited by Raúl N Guedes – UFV Received 9 November 2014 and accepted 14 March 2015 * Sociedade Entomológica do Brasil 2015
Abstract The house fly, Musca domestica L. (Diptera: Muscidae), is a pest of livestock and has the ability to develop resistance to different insecticides. We assessed the fluctuations in seasonal stability of house fly resistance to insecticides from poultry facility populations in Pakistan. House fly populations were collected from poultry facilities located at Khanewal, Punjab, Pakistan in three seasons (July, November, and March) to investigate the fluctuations in their resistance to conventional (organophosphate, pyrethroid) and novel chemistry (spinosyn, oxadiazine, neonicotinoid) insecticides. Laboratory bioassays were performed using the feeding method of mixing insecticide concentrations with 20% sugar solutions, and cotton pads dipped in insecticide solutions were provided to tested adult flies. Bioassay results showed that all house fly populations had varying degrees of susceptibility to tested insecticides. Comparisons between populations at different seasons showed a significant fluctuation in susceptibility to organophosphate, pyrethroid, spinosyn, oxadiazine, and neonicotinoid insecticides. Highest resistant levels were found for organophosphate when compared with other tested insecticides. The resistance to conventional insecticides decreased significantly in March compared with July and November, while resistance to oxadiazine and avermectins decreased significantly in November. However, resistance to spinosad and imidacloprid remained stable throughout the seasons. All conventional and novel chemistry insecticides were significantly correlated with each other in all tested seasons except nitenpyram/lambda-cyhalothrin and nitenpyram/ imidacloprid. Our data suggests that the variation in house fly resistance among seasons could be due to fitness costs or to the cessation of selection pressure in the off-season. These results have significant implications for the use of insecticides in house fly management.
Introduction The house fly, Musca domestica L. (Diptera: Muscidae), is a serious pest of livestock and humans (Scott et al 2000, Kaufman et al 2001, Deacutis et al 2006), causing health and environmental problems by vectoring diseases from animals to man and animal to animal. House flies reproduce on
all eatable materials and wastes and are a known vector of more than 100 disease pathogens, including bacteria, protozoa, helminths, and viruses (Förster et al 2007, Acevedo et al 2009, Khan et al 2012, Abbas et al 2014a). Outbreaks of diarrheal diseases are associated with seasonal abundance of house flies in urban and rural settings of many countries, including Pakistan (Graczyk et al 2001, Khan & Akram 2014).
Abbas et al
The house fly is also a vector of the bird flu virus, an avian influenza that is a serious problem in poultry throughout the world (Barin et al 2010, Wanaratana et al 2011). Millions of domestic poultry flocks are affected by the avian influenza virus which has caused more than 150 deaths of humans globally (Otte et al 2007). In areas of poultry farming, like Punjab Pakistan, uncovered poultry manure provides an ideal condition for growth and reproduction of house flies. Highdensity populations of flies irritate workers, stress hens, and reduce the aesthetic value of livestock, leading to economic losses (Acevedo et al 2009, Abbas et al 2014a). Synthetic insecticides, including organophosphate, carbamate, pyrethroid, and novel chemistry classes, have been used to control the house fly worldwide, including Pakistan. Judicious and appropriate insecticide applications are helpful in conditions where high densities of the house fly are associated with avian influenza in poultry (Nielsen et al 2011, Wanaratana et al 2011) and diarrhea in humans (Chavasse et al 1999, Khan & Akram 2014), but season-specific use of insecticides is required. However, inappropriate chemical use and poultry manure stored in open places could result in the development of resistance to insecticides by house flies. These factors may be responsible for avian influenza and diarrhea cases in poultry and humans, respectively, particularly in developing countries. This resistance development is also promoted by a number of biological traits such as adaptability to different environments, high fecundity, a short developmental time, and cross-resistance (Kaufman et al 2010a, Khan et al 2013b). Resistance to all chemical classes is common in house flies worldwide (Scott et al 2000, Acevedo et al 2009, Kaufman et al 2010b, Khan et al 2013a,b, 2014a, Abbas et al 2014a,b). The determination of the stability of insecticide resistance has practical implications in developing effective resistance management strategies (Khan et al 2014b, Afzal et al 2015). The removal of insecticides from spray schedules may bring the resistance level down if resistance is unstable, and consequently, the efficacy of an insecticide can be extended. A decrease in resistance has been reported for insecticideselected insect populations in the field and laboratory (Carriére & Tabashnik 2001). Effective resistance management programs depend upon different mechanisms of resistance and factors that enhance susceptibility recovery. A reduction in resistance levels may be due to the negative effects of resistance genes on fitness components without insecticide selection pressure. When insecticide exposure is not a constant factor, the susceptibility of resistant individuals may change in the absence of selection pressure under laboratory conditions (Roush 1993, Kristensen et al 2000, Abbas et al 2014b). We assessed the fluctuations in insecticide resistance of house fly populations from Khanewal, Punjab, Pakistan. House fly peak densities start in March and continue until
August. Therefore, house fly populations were collected in different seasons (late summer, early winter, and early spring) to assess the variation in susceptibility to pyrethroids (cypermethrin, lambda-cyhalothrin), organophosphate (chlorpyrifos), neonicotinoids (imidacloprid, acetamiprid, nitenpyram), spinosyn (spinosad), oxadiazine (indoxacarb), and avermectins (abamectin and emamectin benzoate). The results of this study can have a significant role in developing strategies for house fly resistance management through the selection of the most appropriate insecticide to deal with the unstable nature of resistance in specific months of the year for the management of house flies.
Material and Methods Insect rearing About 200 adult house flies were collected from a poultry farm located at Khanewal (32°4′50N, 73°38′10E) in three different seasons denoted by March, July, and November with a sweep net. Adult flies were kept in meshed plastic jars (34× 17 cm) and fed on a mixture of sugar and powdered milk (1:1 w/w). Cotton wicks soaked with water were provided in a Petri dish in order to supplement moisture requirements. Larvae were reared on an artificial diet comprising powdered milk, sugar, yeast, grass meal, and wheat bran (1.5:1.5:5:5:20 w/w) and 65 mL of water (Abbas et al 2014a). The colony was maintained under laboratory conditions according to Abbas et al (2014a). The susceptible strain was collected from an insecticide-free area (Multan) and maintained in the laboratory without exposure to insecticides. Insecticides Commercial formulated insecticides were used for bioassays including conventional: chlorpyrifos (Lorsban® 40EC, Arysta Life Sciences), cypermethrin (Arrivo® 10EC, FMC), and lambda-cyhalothrin (Karate® 2.5EC, Syngenta); and newer chemistries: spinosad (Tracer® 240SC, Arysta Life Sciences), indoxacarb (Steward® 150SC, Arysta Life Sciences), abamectin (Alarm® 1.8EC, DJC), emamectin benzoate (Proclaim® 019EC, Syngenta), acetamiprid (Mospilan® 70WP, Arysta Life Sciences), imidacloprid (Confidor® 20SL, Bayer Crop Science), and nitenpyram (Paranol® 10EC, Kenzo Agro Chemicals). Toxicological bioassays The toxicities of the tested insecticides were assessed by using a feeding bioassay (Kaufman et al 2006). Ten 2–3day-old male and female flies were provided with a cotton wick (3 cm) soaked in 20% sugar solution plus insecticide and
Stability of Field Resistance to Selected Insecticides in House Flies
kept in plastic jars (14×9 cm) (Abbas et al 2014b). Five concentrations were prepared as serial dilutions for each insecticide, and each concentration was replicated three times (10 flies/replicate). The range of concentrations was 8–128 μg· mL−1 for organophosphate, pyrethroid, and neonicotinoid; 0.125–2 μg·mL−1 for avermectins; and 1–16 μg·mL−1 for spinosyn and oxadiazine in all tested strains. Cotton wicks soaked in 20% sugar solution without insecticide were provided to control flies (3 replicates of 10 flies). Cotton wicks were hydrated (without sugar solution) after 24 and 48 h to avoid wick drying (Kaufman et al 2006). All flies were kept under laboratory conditions as earlier described. Mortality data was assessed 48 h after exposure to conventional and 72 h after exposure to newer chemistry insecticides. Ataxic flies were considered as dead (Abbas et al 2014a). Data analysis Concentration response data were analyzed by probit analysis (Finney 1971) with POLO software (Software 2005) to determine LC50 values, their 95% confidence intervals (CI), slopes, and their standard errors. Control mortality was corrected by the formula of Abbott (1925), whenever required. Resistance ratio (RR) and its 95% CI were calculated by dividing the LC50 value and its 95% CI of test strains by the LC50 of the susceptible strain (Ban et al 2012). LC50 values were not considered significantly different when their 95% CI overlapped. The resistance ratio was considered significant if the 95% CI did not include the value of 1 (Robertson & Preisler 1992). Variation in resistance per month (R) was estimated with the following formula: R ¼ logðfinal LC50 Þ−log ðinitial LC50 Þ=n In the above equation, n indicates the months between two collections. Positive and negative values for R indicate the increase and decrease in resistance, respectively. Coefficient of correlation of mortality responses to insecticides were used to calculate the coefficient of determination by taking square of the coefficient of correlation of responses between any of two tested insecticides (Sayyed et al 2005). LC50 values were not considered significantly different when their 95% CI overlapped (Robertson & Preisler 1992).
Results Toxicity of insecticides to a house fly-susceptible strain The susceptible strain of the house fly was more susceptible to the newer chemistry insecticides. Abamectin, indoxacarb, emamectin benzoate, and spinosad were more toxic compared
with other tested insecticides. Chlorpyrifos, lambda-cyhalothrin, cypermethrin, and nitenpyram were equally toxic. Imidacloprid and acetamiprid were less toxic (Table 1). The LC50 values of spinosad, indoxacarb, abamectin, and emamectin benzoate were significantly lower compared with other insecticides tested except chlorpyrifos (95% CI did not overlap). There was no significant difference in LC50 values of cypermethrin, lambdacyhalothrin, acetamiprid, and nitenpyram (95% CI overlapped). The LC50 of imidacloprid was higher compared with all other tested insecticides (95% CI did not overlap) (Table 1). Stability of resistance to conventional insecticides Resistance to conventional insecticides in poultry facilitycollected strains varied significantly with the season (Table 2). In populations collected at 3-month intervals, the resistance level for chlorpyrifos decreased significantly in March compared with July and November but increased slightly in November compared with the strain collected in July. The resistance to cypermethrin and lambda-cyhalothrin decreased significantly in March compared with July and November. The declined rate of resistance to cypermethrin (−0.2) and lambda-cyhalothrin (−0.3) was similar for the strain collected in March. Stability of resistance to newer chemistry insecticides Resistance to newer chemistry insecticides varied significantly with the season in the poultry facility-collected house fly strains (Table 2). The resistance to spinosad remained stable throughout the season in which strains were collected. The resistance to indoxacarb, abamectin, and emamectin benzoate decreased significantly in November compared with the strains collected in July and March. However, resistance remained stable for the strains collected in July and March. Table 1 Toxicity of insecticides to the susceptible strain of Musca domestica. Insecticide
LC50 (95% CI) (μg·mL−1)
Slope (±SE)
Chlorpyrifos Cypermethrin Lambda-cyhalothrin Spinosad Indoxacarb Abamectin Emamectin benzoate Imidacloprid
1.0 (0.5–1.5) 2.1 (1.6–2.6) 1.9 (1.4–2.5) 0.4 (0.3–0.6) 0.4 (0.2–0.5) 0.2 (0.1–0.4) 0.4 (0.3–0.6) 6.7 (3.8–19)
1.8±0.4 2.6±0.4 2.1±0.3 1.7±0.3 1.6±0.3 1.3±0.3 1.5±0.3 0.9±0.3
Acetamiprid Nitenpyram
3.2 (2.4–4.2) 2.5 (1.8–3.3)
2.6±0.4 2.0±0.3
Number of adult flies tested including controls was 180. CI confidence intervals.
Abbas et al Table 2
Seasonal variation in Musca domestica resistance to different insecticides.
Insecticide
Chemical family
Season
LC50 (95% CI) (μg·mL−1)
Slope
RR (95% CI)a
Rb
Chlorpyrifos
Organophosphate
Cypermethrin
Pyrethroid
July November March July November March July November March July November March July November March July November
48 (31–72) 74 (54–114) 16 (9.9–23) 31 (23–41) 25 (19–34) 8.7 (4.9–13) 66 (49–91) 63 (41–122) 6.7 (1.9–11) 2.9 (1.7–4.4) 3.3 (1.6–6.1) 0.9 (0.01–2.1) 3.5 (2.5–4.8) 1.1 (0.2–2) 6.6 (4.1–10) 0.5 (0.3–0.7) 0.1 (0.04–0.2)
2.1±0.5 1.8±0.3 1.9±0.4 2.6±0.4 2.1±0.3 1.6±0.4 2.2±0.4 2.2±0.3 1.9±0.5 1.5±0.3 2.2±0.3 0.9±0.3 2.2±0.4 0.9±0.3 3.4±1.3 2.1±0.4
48 (31–72) 74 (54–114) 16 (9.9–23) 15 (11–20) 12 (9–16) 4 (2–6) 34 (26–48) 32 (22–64) 3 (1–6) 7.3 (4.3–11) 8.3 (4–15) 2.3 (0.03–5.3) 10 (6.3–12) 2.8 (0.5–5) 19 (10–25) 2.5 (1.5–3.5)
– 0.1 −0.2 – −0.03 −0.2 – −0.01 −0.3 – 0.02 −0.2 – −0.2 0.1 –
1.3±0.3
0.5 (0.2–1)
−0.2
March July November March July November March July November March July November March
0.5 (0.3–0.7) 0.8 (0.5–1.1) 0.1 (0.03–0.2) 1.6 (0.9–9) 16 (11–21) 17 (10–25) 16 (4.6–28) 31 (21–55) 79 (57–225) 14 (6.2–20) 8 (5.4–11) 32 (16–65) 14 (8.8–20)
1.6±0.3 2.7±0.6 1.0±0.3 1.2±0.4 2.2±0.4 1.4±0.3 1.2±0.4 1.7±0.4 1.9±0.5 1.6±0.4 2.4±0.4 1.8±0.3 1.7±0.3
2.5 (1.5–3.5) 4 (1.3–2.8) 0.3 (0.1–0.5) 4 (2.3–23) 2.4 (1.6–3.1) 2.5 (1.5–3.7) 2.4 (0.7–4.2) 10 (6.6–17) 25 (18–70) 4.4 (1.9–6.3) 3.2 (2.2–4.4) 13 (6.4–26) 5.6 (3.5–8)
0.00 – −0.3 0.1 – 0.01 −0.01 – 0.1 −0.1 – 0.2 0.1
Lambda-cyhalothrin
Spinosad
Spinosyn
Indoxacarb
Oxadiazine
Abamectin
Avermectin
Emamectin benzoate
Imidacloprid
Neonicotinoid
Acetamiprid
Nitenpyram
Number of adult flies tested including controls was 180. a
Resistance ratio calculated as LC50 of field population/LC50 of susceptible population.
b
Rate of decrease of resistance.
The declined rate of resistance against indoxacarb (−0.2), abamectin (−0.2), and emamectin benzoate (−0.3) was similar for the strain collected in November. The resistance to imidacloprid remained stable throughout the season in which strains were collected. However, the resistance to acetamiprid and nitenpyram increased significantly in November compared with the strain collected in July and March. The resistance to acetamiprid and nitenpyram did not decrease significantly in July compared with March.
Correlation in insecticides All conventional and newer chemistry insecticides depicted significant correlations with each other in all tested seasons
except nitenpyram/lambda-cyhalothrin and nitenpyram/ imidacloprid, which showed a non-significant correlation in the population collected in July. Similarly, acetamiprid/ cypermethrin, acetamiprid/lambda-cyhalothrin, and nitenpyram/acetamiprid showed non-significant correlation in the population collected in November (Table 3).
Coefficient of determination The coefficient of determination for cypermethrin/ chlorpyrifos decreased between July and November while it increased between November and March. The coefficient of determination for lambda-cyhalothrin/chlorpyrifos and lambda-cyhalothrin/cypermethrin increased between July
Stability of Field Resistance to Selected Insecticides in House Flies Table 3
Correlations in mortality to insecticides in different seasons for different populations of Musca domestica.
March Cypermethrin Lambda-cyhalothrin Acetamiprid Imidacloprid Nitenpyram July Cypermethrin Lambda-cyhalothrin Acetamiprid Imidacloprid Nitenpyram November Cypermethrin Lambda-cyhalothrin Acetamiprid Imidacloprid Nitenpyram
Chlorpyrifos
Cypermethrin
Lambda-cyhalothrin
Acetamiprid
Imidacloprid
0.99** 0.97** 0.97** 0.80** 0.96**
0.93* 0.97** 0.99*** 0.99**
0.94* 0.92* 0.90*
0.99** 0.93*
0.98**
0.98** 0.98** 0.98** 0.99*** 0.90*
0.96** 0.97** 0.97** 0.95*
0.99*** 0.99*** 0.84 ns
0.98** 0.88*
0.85 ns
0.97** 0.98** 0.93* 0.98**
0.99*** 0.85 ns 0.98**
0.85 ns 0.99***
0.89*
0.95**
0.94*
0.98**
0.83 ns
0.98**
ns not significant. *P≤0.05; **P≤0.01; ***P≤0.001.
and November while it decreased between November and March (Fig 1a). The coefficient of determination of acetamiprid/chlorpyrifos or cypermethrin or lambdacyhalothrin decreased between July and November but increased between November and March (Fig 1b). The coefficient of determination for imidacloprid/ acetamiprid decreased between July and November and increased between November and March. The coefficient of determination increased for imidacloprid/cypermethrin while it decreased for imidacloprid/chlorpyrifos from July to March. The coefficient of determination for imidacloprid/ lambda-cyhalothrin remained stable between July and November but decreased between November and March (Fig 1c). The coefficient of determination for nitenpyram/ chlorpyrifos increased from July to March. The coefficient of determination for nitenpyram/cypermethrin decreased between July and November while it increased between November and March. In contrast, the coefficient of determination for nitenpyram/lambda-cyhalothrin increased between July and November and decreased between November and March. The coefficient of determination for nitenpyram/acetamiprid decreased between July and November but increased between November and March. The coefficient of determination for nitenpyram/ imidacloprid increased between July and November and remained stable between November and March (Fig 1d).
Discussion Organic insecticides are the major alternative available for house fly control at livestock farms. However, the development of house fly resistance to insecticides slows down the effectiveness of new preparations, making quite difficult the selection of the most effective insecticides (Khan et al 2013a). The use of insecticides with long residual action in close vicinities of productive areas exerts a strong selection pressure that increases resistance development (Scott et al 2000). Conventional (pyrethroids and organophosphates) and newer chemistries (spinosyn, oxadiazine, and avermectin) are commonly used for the management of house fly in livestock farms worldwide, including Pakistan. The fluctuations in insecticide resistance patterns observed in our study suggest that the susceptibility decreased during July and November for chlorpyrifos, cypermethrin, lambdacyhalothrin, spinosad, and acetamiprid. Susceptibility decreased in the months of July and March for indoxacarb, abamectin, and emamectin benzoate, but increased for nitenpyram. Resistance to imidacloprid remained stable throughout the months in which strains were collected. For some insecticides, resistance increased in late summer to early winter and decreased in early spring. In contrast, resistance increased in early spring and late summer and decreased in early winter for some insecticides. This might be due to resistance genes, unmeasured fitness costs,
Abbas et al
B
Coefficient of determinaon
A
1.20
1.00 0.98 0.96 0.94 0.92 0.90 0.88 0.86 0.84 0.82 0.80
1.00 0.80 0.60 0.40
Lambda-Chlor
0.20
Lambda-Cyper July
Coefficient of determinaon
Cyper-Chlor
November Collecon date
0.00 July
March
C
D
1.20
1.20
1.00
1.00
0.80
0.80
0.60
0.60
Imida-Chlor Imida-Cyper Imida-Lambda Imida-Aceta
0.40 0.20
Aceta-Chlor Aceta-Cyper Aceta-Lambda
0.20 0.00
July
November Collecon date
March
March
Niten-Chlor Niten-Cyper Niten-Lambda Niten-Aceta Niten-Imida
0.40
0.00
November Collecon date
July
November Collecon date
March
Fig 1 Variations in coefficients of determination of different combinations of a cypermethrin, lambda-cyhalothrin, and chlorpyrifos; b of acetamiprid, chlorpyrifos, cypermethrin, and lambda-cyhalothrin; c of imidacloprid, chlorpyrifos, cypermethrin, and lambda-cyhalothrin; and d of nitenpyram, chlorpyrifos, cypermethrin, lambda-cyhalothrin, acetamiprid, and imidacloprid from July to March for different populations of Musca domestica.
hybridization of susceptible individuals, and the selection pressure of different insecticides in poultry farms. The low level of resistance to some insecticides during a certain period of the year is due to the cessation of insecticide use in the off-season. In this study, resistance to conventional and newer chemistry insecticides significantly varied from season to season in M. domestica. The highest use of insecticides occurs from March to August because of the high population of the house fly in these months. It is expected that an increase in resistance occurs during these months because resistant adults would have mated and oviposited. Resistance to most of the newer chemistry insecticides tested increased in July and March. However, resistance to organophosphates and pyrethroids decreased in March. Previously, the fluctuation in resistance to different insecticides has been observed in insect pests like Plutella xylostella L. (Sayyed et al 2005). The fluctuation of resistance in our study might be due to the decreased usage of organophosphate and pyrethroid insecticides in March, but increased resistance for newer chemistry insecticides is due to their frequent applications for house fly control. Higher resistance to pyrethroids and organophosphates in November may be because of cross-resistance between these insecticides. Cross-resistance between pyrethroids and organophosphates could be due to the involvement of esterases (Ahmad et al 2007). The house
fly might have developed resistance through different mechanisms, but if the resistance is completely or incompletely dominant, then a minimum of two different mechanisms of resistance can occur (Rahardja & Whalon 1995, Sayyed et al 2005). Previously, an autosomal, incompletely dominant resistance and also the involvement of glutathione-S-transferase, esterase, and microsomal monooxygenase esterase mechanism of pyrethroid resistance were reported for the house fly (Abbas et al 2014b). The variation in resistance could also be due to the involvement of fitness costs in the absence of selection pressure from insecticides. Selection pressure with isolan (1-isopropyl-3-methyl-5-pyrazolyl dimethyl carbamate) led to the development of a relatively stable resistant phenotype in this house fly strain, suggesting fitness costs are not involved. In contrast, selection pressure with misopropylphenyl methyl carbamate on the house fly strain produced an unstable phenotype, suggesting high fitness costs are involved (Georghiou 1964). In a previous experiment, a house fly strain collected from the Multan region showed a dose-dependent incomplete dominance of resistance to lambda-cyhalothrin that remained unstable in the absence of selection pressure, which may reveal a high fitness cost (Abbas et al 2014b). The results of our study may have important implications for house fly resistance management to pyrethroids and organophosphates.
Stability of Field Resistance to Selected Insecticides in House Flies
A simple alternate insecticide use strategy can be easily practiced in tropical and sub-tropical climatic conditions. Applications of insecticides at a specific season when susceptibility is higher can lead to a greater change in frequency of resistance alleles. Therefore, alternate use of insecticides belonging to different groups should be recommended and inhibit the application of insecticides of the same group repeatedly. To prevent diarrheal and avian influenza epidemics, house fly outbreaks should be controlled by using appropriate insecticides suited to the prevailing environmental situations. Moreover, alternate use of the most effective insecticides in the most suitable season of the year will reduce selection pressure and ultimately delay the development of insecticide resistance (Abbas et al 2014a, Khan & Akram 2014). The house fly collected from Khanewal showed high susceptibility to spinosad, indoxacarb, abamectin, and emamectin benzoate, so these compounds could be used for this strategy. Poultry farmers have major problems with insecticide use for the management of poultry pests in Pakistan. Inappropriate chemical use at incorrect doses, bad spray methods, and schedule are common. Moreover, adulterated chemical formulations and poor extension services are of significant importance. If the earlier mentioned problems are addressed in a proper manner and farmers are trained for proper use of insecticides and motivated to implement newly developed strategies and techniques, then these problems can be solved in the future. On the basis of our data, we recommend that chlorpyrifos, lambdacyhalothrin, cypermethrin, spinosad, and acetamiprid should be used in March, while indoxacarb, abamectin, and emamectin benzoate in November and nitenpyram in July for house fly control. Acknowledgments The authors are highly grateful to Prof. Dr. Gerald Wilde, Kansas State University, USA for the critical review of manuscript to improve English language.
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