Veterinary Parasitology, 35 (1990) 93-101 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
93
Ecological Aspects of Four Species of Ticks Found on Cattle in Salta, N o r t h w e s t A r g e n t i n a A.A. GUGLIELMONE, A.J. MANGOLD, D.H. AGUIRRE and A.B. GAIDO
Unidad Regional de Investigacidn en Sanidad Animal del Noroeste Argentino, Instituto Nacional de Tecnologia Agropecuaria, C.C. 228, 4400 Salta (Argentina) (Accepted for publication 13 July 1989)
ABSTRACT Guglielmone, A.A., Mangold, A.J., Aguirre, D.H. and Gaido, A.B., 1990. Ecological aspects of four species of ticks fbund on cattle in Salta, northwest Argentina. Vet. Parasitol., 35: 93-101. The seasonal activity of Amblyomma cajennense, Amblyomma neumanni, Amblyomma parvum and Boophilus microplus on cattle was studied in a ranch located in the northern part of the phytogeographical district of the Chaco Serrano where the habitat had suffered minimal human disturbance. The female ticks on one side of 10-25 cows were counted at intervals of 20-50 days from 29 October 1985 to 5 November 1986. The percentage of cattle parasitized with larvae and nymphs of Amblyomma was recorded, along with the proportion corresponding to the different species. Collection of ticks from the ground cover vegetation in areas with and without forest was performed using the dragging technique. B. microplus was found all year round; peaks of abundance were observed in May (55 females per cow/2) and November 1986 (71 females per cow/2). The peak in November was unexpected and possibly due to a higher stocking rate around watering places and poor nutrition at the end of the dry season. A. cajennense appears to produce a generation a year. Larvae were more abundant from June to August, nymphs from August to November and females from November (34 per cow/2) to January (15 per cow/2). A. neumanni showed a cycle corresponding to a generation every 3 years regulated via diapause that involves, at least, all the summer months. The peak of abundance for larvae, nymphs and females occurred in late autumn-early winter. The highest number of females (44 per cow/2) was recorded in June. A. parvum females were found from October to November with a peak number (4 per cow/2 ) in December. Neither nymphs nor larvae of A. parvum were detected. Host-seeking stages were recovered mainly from the forested areas; all of them were A. cajennense and A. neumanni. A discussion related to control measures is presented.
INTRODUCTION
The tick species most frequently found on cattle in northwest Argentina are the one-host tick, Boophilus microplus, and three representatives of the genus Amblyomma: A. cajennense, A. neumanni and A. parvum (Guglielmone et al., 0304-4017/90/$03.50
© 1990 Elsevier Science Publishers B.V.
94
A.A. G U G L I E L M O N E E T AL.
1981; Guglielmone and Hadani, 1982; Mangold et al., 1987). They are considered a major cause of direct losses to the livestock industry. Moreover, B. microplus is recognized as the vector of Babesia boris and Babesia bigemina, b u t the role of these species of Amblyomma on the transmission of pathogens to local cattle is unknown. Efficient control of these tick species requires information on the seasonal distribution and other ecological aspects of the different developmental stages. To this end, the present study was carried out on a farm where cattle were maintained under extreme range conditions and with few substantial changes since their introduction, centuries ago.
MATERIALS AND METHODS The study site comprised 30 000 ha with a population of ~ 4000 cattle. It was located ~ 25 °02'S and 64 ° 5 8 ' w in the north of the phytogeographical district of the Chaco Serrano whose climatic and phytogeographical characteristics were described previously (Guglielmone and Hadani, 1982 ). This site was selected because there are no internal fences, acaricides have not been applied, the natural forest has been preserved in most areas, the alimentation of cattle is based on native grasses and the cattle are of the "regional" type, originating from uncontrolled crosses between Spanish and British Bos taurus. Twelve visits, each of a period of 20-50 days, were made from 29 October 1985 to 5 November 1986.
Evaluation of tick infestations Tick counts were performed on one side of 10-25 cows taken at random from the herd gathered around a dam between 09.00 and 10.00 h. All females of Amblyomma, with the exception of the engorged ticks, were counted and discriminated according to species without removing them from the hosts. Tick numbers of B. microplus were evaluated counting all females 4.5-8.0 mm long (Wharton and Utech, 1970). The larval and nymphal infestation of Amblyomma was registered as a percentage of cattle infested due to the impossibility of counting these stages with a reasonable degree of accuracy. To evaluate the proportion according to tick species, a maximum of 100 engorged larvae or nymphs were collected on each sampling date. T h e y were maintained at 27 + 1 ° C, 83-86% relative humidity ( R H ) in darkness until moulting to obtain unfed, clean specimens suitable for identification.
95
ECOLOGICAL ASPECTS OF TICKS, NORTHWEST ARGENTINA
Evaluation of host-seeking stages on the ground cover vegetation On each occasion, five areas of 50 m 2 each at a forested and an open zone were sampled applying the dragging technique with pieces of white flannelette (2 × 1 m) as described elsewhere (Guglielmone et al., 1986). The host-seeking larvae captured by dragging were allowed to feed on rabbits, and the engorged ticks recovered were maintained to moult as described above and classified as unfed nymphs.
Climatic data The temperature and RH at ground level were registered using thermohygrographs set up in forested and open areas from March 1986. Rainfall data were registered for all the study period.
101 . ,,
•
!
: .
|
II
|
. . . .
,
Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov T985 1986 f t t t I t ~ t t 1 t t
Fig. 1. Seasonal distribution ot temale ticks expressed as average per ¢ow/2. t indicates sampling dates.
96
A.A. (IUGLIELMONE ET AL.
RESULTS
The seasonal distribution of female ticks on cattle is presented in Fig. 1. B.
microplus and A. cajennense were found all year round. The former showed peaks of infestation in autumn and spring; the latter reached a m a x i m u m from late spring to mid-summer. The highest burdens of B. microplus were registered in May and November 1986 with 55 and 71 ticks per cow/2, respectively. The peak number ofA. cajennense was 34 in November 1985. A. neumanni was more abundant from late autumn to early winter; the highest average burden was 44 ticks in June 1986. A. parvum was found in low numbers in spring and summer; the mean m a x i m u m burden was 4 ticks per cow/2 in December 1985. The percentage of cattle infested with larvae and nymphs of Amblyomma is illustrated in Fig. 2. All the cattle carried larvae of Amblyomma from May to August and nymphs from June to November 1986. Larvae and nymphs of A. neumanni appeared earlier than those of A. cajennense. Unengorged larvae (species not determined) were found on a few cows in October 1985 and 1986. Neither larvae nor nymphs of A. parvum were found. Except for two nymphs of A. cajennense, all the host-seeking stages were found in the forested area (Fig. 3). All the stages of A. cajennense and larvae and nymphs of A. neurnanni were detected at about the same time that they were found on cattle. No adults of A. neumanni, larvae of B. microplus or any stage of A. parvum were found on the vegetation. Climatic data are presented in Fig. 4. The total rainfall was 514 mm. As expected, m a x i m u m and minimum temperatures were higher in the open area. M i n i m u m RHs were generally lower in the open area, whereas no substantial 0 Ac 33Ac 5Ac 64Ac 100 An 67An 95An 36An
100. 80.
Larvae
60. 40. SU
SU
u
100 .£ "~ 80. 60.
20.
24A~ 76An
44 ~, 'A~i iA~ 8~A~ 89A~ ~ 111 Xn
36 :~i ,An .An
Nymphs 40Ac 60 An
0 Ac
100 ~n Oct Nov' Dec'Jan'Feb'Mar Apt'May Jun'Jul 1985 1986 t ~ t I t t t t 't
rAug Sep Oct Nov t
~
t
Fig. 2. S e a s o n a l distribution of the percentage of cattle infested with larvae and nymphs of A. neumanni ( A n ) ( • ) a n d A. cajenueuse (Ac) ( [] ). The proportions per tick species are indicated above e a c h bar. A b a r = 1 0 0 % , irrespective of its height. ? indicates sampling dates. SU = Amblyomma species n o t d e t e r m i n e d .
ECOLOGICALASPECTSOF TICKS, NORTHWESTARGENTINA
97
A, cajennense
ymphs :I
I I
• ,. 2
Adults
i
m,m ct' o
I
£
A. neumanni 100.
Larvae
! 2i
I
Nymphs .
.
,
m
,
,
I
•
Oct'Nov Dec Jan Feb"Mar'tS~'AP19MaYJUnTJul Aug Sep O¢{ Nov' ?1985? f
t
f
?
~
f
Fig. 3. Mean number of ticks per species and stages collected w i t h the dragging forested area. ? indicates sampling dates.
technique in the
registered in the m a x i m u m RHs for both areas. The cycles of A. neumanni and A. cajennense are presented in Fig. 5. They are based on the presence, absence and abundance of larvae, nymphs and adults on cattle and on vegetation. For this purpose, the larval infestations of October 1985 and 1986 were considered as a combination of both species. The abundance of larvae, nymphs and adults of A. cajennense was sequential, whereas all stages ofA. neumanni were more abundant from May to July. differences were
DISCUSSION The climate was characterized by the concentration of rainfall in summer, therefore the peak infestation with B. microplus was expected to occur in aut u m n as a result of suitable conditions of temperature and humidity for egg development in the previous season (Guglielmone et al., 1981). Nevertheless, the highest tick burden was found in November 1986 when the dryness of the preceding months was supposed to affect the egg development and survival of unfed larvae of B. microplus (Wilkinson, 1970). This peak of B. microplus in spring was also recorded in two other areas of northwest Argentina (Gugliel-
98
A.A.GUGLIELMONEET AI,.
@a
0~8@@0000
RELATIVE HUMIDITY
Fig. 4. Climatic parameters values.
-100 @E,
@OQOb
-80 -60
registered
%
in the open ( 0 ) and forested
(0 ) areas. 0 1coincidental
mone et al., 1981; Mangold et al., 1987). Poor nutrition of cattle during the dry season weakens their resistance to B. microplus (Sutherst et al., 1983); this, in conjunction with the increase in the stocking rate around watering places, could be responsible for the peak of infestation during the spring. These factors may help to overcome the negative impact of the climate on the population dynamics of B. microplus, increasing the chances of the larvae finding and surviving on a host. All parasitic stages of A. neumanni and A. cajennense and adults of A. paruum were found on cattle. This agrees with a previous report which suggests that cattle are able to maintain the life cycle of the first two species of Amblyomma in the environment, but not A. parvum (Guglielmone and Hadani, 1982). The absence of all the stages of A. neumanni from January to March, followed afterwards by their simultaneous abundance (Fig. 5 ) , indicates a trien-
ECOLOGICAL ASPECTS OF TICKS, NORTHWEST ARGENTINA
99
\ _/Nymps
Fig. 5. N a t u r a l cycles of A. neumanni (A.n) a n d A. cajennense (A.c) ( [E, presence; [], a b u n d a n c e ).
nial life cycle regulated via summer diapause. This phenomenon tends to solve problems of adaptation of various arthropods (Masaki, 1980). The seasonality ofA. neumanni may be aimed at minimizing the competition with adults of A. cajennense for the same hosts. The sequential abundance of the different instars of A. cajennense indicates that there is probably one generation per year. The abundance of adults in the hottest months and of larvae and nymphs during the dry season is coincident with various observations in America and the Caribbean region (Aragao, 1936; Fairchild et al., 1966; Smith, 1975; Guglielmone and Hadani, 1982; Mangold et al., 1987 ). The lower density of ticks in the open area than in the forested area could be related to higher temperatures in the former (Fig. 4); this shortens the longevity of ticks due to dehydration (Lees, 1946) or to high metabolic rate (Tukahirwa, 1976). Host preference for the forested habitat could be another important factor regulating tick populations on the ground cover vegetation, however this was not investigated. The results of this study indicate that it could be feasible to simultaneously reduce the peak burden of all the stages ofA. neumanni, the larval population of A. cajennense and the autumn generation of B. microplus with chemical treatments of cattle between late autumn and early winter. This measure will probably affect the population of the next instars of A. cajennense, and the next generations ofA. neumanni and B. microplus. However, the host range of A. neumanni and A. cajennense is wide (Ivancovich, 1973; Guglielmone and
100
A.A.GUGLIELMONEET AI,.
Hadani, 1981 ). Therefore a quantitative evaluation of the role of other mamreals in supporting both species of Amblyomma is required to develop a sound strategy of tick control based on treatment of cattle with acaricides. Tick-resistant cattle (Bos taurus × Bos indicus ) are useful to control B. microplus (Sutherst and Utech, 1981 ) and some species ofAmblyomma (Bonsma, 1944; Strother et al., 1974). However their resistance to A. cajennense and A. neumanni has not been evaluated. This warrants further investigation since tick-resistant cattle are a better alternative to control ticks because they will delay the appearance of tick populations resistant to chemicals, a feature that sooner or later arises with the use of non-biological pesticides. ACKNOWLEDGEMENTS
We acknowledge the secretarial contribution of Ms. M.R. Fuke and the critical revision of the manuscript by Dr. E.J.A. Spath.
REFERENCES Aragao, H. de B., 1936. Ixodidas brasileiros e de alguns paizes limitrophes. Mem. Inst. Oswald() Cruz, 31: 759-843. Bonsma, J.C., 1944. Hereditary heartwater-resistant characters in cattle. Farming S. Afr., 19:71 96. Fairchild, G.B., Kohls, G.M. and Tipton, V.J., 1966. The ticks of Panama (Acarina: Ixodoidea). In: R.L. Wenzel and V.J. Tipton (Editors), Ectoparasites of Panama. Field Museum of Natural History, Chicago, pp. 167-219. Guglielmone, A.A. and Hadani, A., 1981. La distribucidn geogr~fica de Amblyomma neurnanni Ribaga, 1902 en la Argentina. Gac. Vet., 43: 754-760. Guglielmone, A.A. and Hadani, A., 1982. Amblyomma ticks fbund on cattle in the Northwest of Argentina. Ann. Parasitol. Hum. Comp., 57:91 97. Guglielmone, A.A., Hadani, A., Mangold, A.J., de Haan, L. and Bermddez, A.C., 1981. Garrapatas (Ixodoidea-Ixodidae) del ganado bovino en la provincia de Salta: especies y carga en cinco zonas ecol6gicas. Rev. Med. Vet. (Buenos Aires), 62: 194-205. Guglielmone, A.A., Hadani, A. and Mangold, A.J., 1986. Empleo del didxido de carbon() para la captura de ninfas y adultos de Amblyomma neumanni y Amblyomma cajennense. Rev. Med. Vet. (Buenos Aires), 67: 238-245. Ivancovich, J.C., 1973. Las garrapatas del Chaco y Formosa. Primera comunicacidn. Rev. Invest. Agropec. Ser. 4, PatoL Anim., 10:9 24. Lees, A.D., 1946. The water balance in Ixodes ricinus and certain other species of ticks. Parasitology, 37:1 20. Mangold, A.J., Bermddez, A.C., Kuhne, G.I. and Guglielmone, A.A., 1987. Garrapatas (IxodoideaIxodidae et Argasidae) del ganado bovino en Santiago del Ester(). II. Especies y carga en el noreste y sudoeste de la provincia. Rev. Med. Vet. (Buenos Aires), 68: 142-146. Masaki, S., 1980. Summer diapause. Annu. Rev. Entomol., 25: 1-25. Smith, M.W., 1975. Some aspects of the ecology and life cycle of Amblyomma cajennense (Fabricius, 1787) in Trinidad and their influence on tick control measures. Ann. Trop. Med. Parasitol., 69: 121-129. Strother, G.R., Burns, E.C. and Smart, L.I., 1974. Resistance of purebreed Brahman, Hereford
ECOLOGICAL ASPECTS OF TICKS, NORTHWEST ARGENTINA
101
and Brahman×Hereford crossbreed cattle to the lone star tick, Amblyomma americanum (Acarina: Ixodidae). J. Med. Entomol., 11: 559-563. Sutherst, R.W. and Utech, K.B.W., 1981. Controlling livestock parasites with host resistance. In: D. Pimentel (Editor), CRC Handbook of Pest Management in Agriculture. Vol. II. CRC Press, Boca Raton, FL, pp. 384-409. Sutherst, R.W., Kerr, J.D., Maywald, G.F. and Stegeman, D.A., 1983. The effect of season and nutrition on the resistance of cattle to the tick Boophilus microplus. Aust. J. Agric. Res., 34: 329-339. Tukahirwa, E.M., 1976. The effects of temperature and relative humidity on the development of Rhipicephalus appendiculatus Neumann (Acarina, Ixodidae). Bull. Entomol. Res., 66:301 312. Wharton, R.H. and Utech, K.B.W., 1970. The relation between engorgement and dropping of Boophilus microplus (Canestrini) (Ixodidae) to the assessment of tick numbers on cattle. J. Aust. Entomol. Soc., 9: 171-182. Wilkinson, P.R., 1970. Factors affecting the distribution and abundance of the cattle tick in Aus~ tralia. Observations and hypotheses. Acarologia, 12: 492-508.
93
Ecological Aspects of Four Species of Ticks Found on Cattle in Salta, N o r t h w e s t A r g e n t i n a A.A. GUGLIELMONE, A.J. MANGOLD, D.H. AGUIRRE and A.B. GAIDO
Unidad Regional de Investigacidn en Sanidad Animal del Noroeste Argentino, Instituto Nacional de Tecnologia Agropecuaria, C.C. 228, 4400 Salta (Argentina) (Accepted for publication 13 July 1989)
ABSTRACT Guglielmone, A.A., Mangold, A.J., Aguirre, D.H. and Gaido, A.B., 1990. Ecological aspects of four species of ticks fbund on cattle in Salta, northwest Argentina. Vet. Parasitol., 35: 93-101. The seasonal activity of Amblyomma cajennense, Amblyomma neumanni, Amblyomma parvum and Boophilus microplus on cattle was studied in a ranch located in the northern part of the phytogeographical district of the Chaco Serrano where the habitat had suffered minimal human disturbance. The female ticks on one side of 10-25 cows were counted at intervals of 20-50 days from 29 October 1985 to 5 November 1986. The percentage of cattle parasitized with larvae and nymphs of Amblyomma was recorded, along with the proportion corresponding to the different species. Collection of ticks from the ground cover vegetation in areas with and without forest was performed using the dragging technique. B. microplus was found all year round; peaks of abundance were observed in May (55 females per cow/2) and November 1986 (71 females per cow/2). The peak in November was unexpected and possibly due to a higher stocking rate around watering places and poor nutrition at the end of the dry season. A. cajennense appears to produce a generation a year. Larvae were more abundant from June to August, nymphs from August to November and females from November (34 per cow/2) to January (15 per cow/2). A. neumanni showed a cycle corresponding to a generation every 3 years regulated via diapause that involves, at least, all the summer months. The peak of abundance for larvae, nymphs and females occurred in late autumn-early winter. The highest number of females (44 per cow/2) was recorded in June. A. parvum females were found from October to November with a peak number (4 per cow/2 ) in December. Neither nymphs nor larvae of A. parvum were detected. Host-seeking stages were recovered mainly from the forested areas; all of them were A. cajennense and A. neumanni. A discussion related to control measures is presented.
INTRODUCTION
The tick species most frequently found on cattle in northwest Argentina are the one-host tick, Boophilus microplus, and three representatives of the genus Amblyomma: A. cajennense, A. neumanni and A. parvum (Guglielmone et al., 0304-4017/90/$03.50
© 1990 Elsevier Science Publishers B.V.
94
A.A. G U G L I E L M O N E E T AL.
1981; Guglielmone and Hadani, 1982; Mangold et al., 1987). They are considered a major cause of direct losses to the livestock industry. Moreover, B. microplus is recognized as the vector of Babesia boris and Babesia bigemina, b u t the role of these species of Amblyomma on the transmission of pathogens to local cattle is unknown. Efficient control of these tick species requires information on the seasonal distribution and other ecological aspects of the different developmental stages. To this end, the present study was carried out on a farm where cattle were maintained under extreme range conditions and with few substantial changes since their introduction, centuries ago.
MATERIALS AND METHODS The study site comprised 30 000 ha with a population of ~ 4000 cattle. It was located ~ 25 °02'S and 64 ° 5 8 ' w in the north of the phytogeographical district of the Chaco Serrano whose climatic and phytogeographical characteristics were described previously (Guglielmone and Hadani, 1982 ). This site was selected because there are no internal fences, acaricides have not been applied, the natural forest has been preserved in most areas, the alimentation of cattle is based on native grasses and the cattle are of the "regional" type, originating from uncontrolled crosses between Spanish and British Bos taurus. Twelve visits, each of a period of 20-50 days, were made from 29 October 1985 to 5 November 1986.
Evaluation of tick infestations Tick counts were performed on one side of 10-25 cows taken at random from the herd gathered around a dam between 09.00 and 10.00 h. All females of Amblyomma, with the exception of the engorged ticks, were counted and discriminated according to species without removing them from the hosts. Tick numbers of B. microplus were evaluated counting all females 4.5-8.0 mm long (Wharton and Utech, 1970). The larval and nymphal infestation of Amblyomma was registered as a percentage of cattle infested due to the impossibility of counting these stages with a reasonable degree of accuracy. To evaluate the proportion according to tick species, a maximum of 100 engorged larvae or nymphs were collected on each sampling date. T h e y were maintained at 27 + 1 ° C, 83-86% relative humidity ( R H ) in darkness until moulting to obtain unfed, clean specimens suitable for identification.
95
ECOLOGICAL ASPECTS OF TICKS, NORTHWEST ARGENTINA
Evaluation of host-seeking stages on the ground cover vegetation On each occasion, five areas of 50 m 2 each at a forested and an open zone were sampled applying the dragging technique with pieces of white flannelette (2 × 1 m) as described elsewhere (Guglielmone et al., 1986). The host-seeking larvae captured by dragging were allowed to feed on rabbits, and the engorged ticks recovered were maintained to moult as described above and classified as unfed nymphs.
Climatic data The temperature and RH at ground level were registered using thermohygrographs set up in forested and open areas from March 1986. Rainfall data were registered for all the study period.
101 . ,,
•
!
: .
|
II
|
. . . .
,
Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov T985 1986 f t t t I t ~ t t 1 t t
Fig. 1. Seasonal distribution ot temale ticks expressed as average per ¢ow/2. t indicates sampling dates.
96
A.A. (IUGLIELMONE ET AL.
RESULTS
The seasonal distribution of female ticks on cattle is presented in Fig. 1. B.
microplus and A. cajennense were found all year round. The former showed peaks of infestation in autumn and spring; the latter reached a m a x i m u m from late spring to mid-summer. The highest burdens of B. microplus were registered in May and November 1986 with 55 and 71 ticks per cow/2, respectively. The peak number ofA. cajennense was 34 in November 1985. A. neumanni was more abundant from late autumn to early winter; the highest average burden was 44 ticks in June 1986. A. parvum was found in low numbers in spring and summer; the mean m a x i m u m burden was 4 ticks per cow/2 in December 1985. The percentage of cattle infested with larvae and nymphs of Amblyomma is illustrated in Fig. 2. All the cattle carried larvae of Amblyomma from May to August and nymphs from June to November 1986. Larvae and nymphs of A. neumanni appeared earlier than those of A. cajennense. Unengorged larvae (species not determined) were found on a few cows in October 1985 and 1986. Neither larvae nor nymphs of A. parvum were found. Except for two nymphs of A. cajennense, all the host-seeking stages were found in the forested area (Fig. 3). All the stages of A. cajennense and larvae and nymphs of A. neurnanni were detected at about the same time that they were found on cattle. No adults of A. neumanni, larvae of B. microplus or any stage of A. parvum were found on the vegetation. Climatic data are presented in Fig. 4. The total rainfall was 514 mm. As expected, m a x i m u m and minimum temperatures were higher in the open area. M i n i m u m RHs were generally lower in the open area, whereas no substantial 0 Ac 33Ac 5Ac 64Ac 100 An 67An 95An 36An
100. 80.
Larvae
60. 40. SU
SU
u
100 .£ "~ 80. 60.
20.
24A~ 76An
44 ~, 'A~i iA~ 8~A~ 89A~ ~ 111 Xn
36 :~i ,An .An
Nymphs 40Ac 60 An
0 Ac
100 ~n Oct Nov' Dec'Jan'Feb'Mar Apt'May Jun'Jul 1985 1986 t ~ t I t t t t 't
rAug Sep Oct Nov t
~
t
Fig. 2. S e a s o n a l distribution of the percentage of cattle infested with larvae and nymphs of A. neumanni ( A n ) ( • ) a n d A. cajenueuse (Ac) ( [] ). The proportions per tick species are indicated above e a c h bar. A b a r = 1 0 0 % , irrespective of its height. ? indicates sampling dates. SU = Amblyomma species n o t d e t e r m i n e d .
ECOLOGICALASPECTSOF TICKS, NORTHWESTARGENTINA
97
A, cajennense
ymphs :I
I I
• ,. 2
Adults
i
m,m ct' o
I
£
A. neumanni 100.
Larvae
! 2i
I
Nymphs .
.
,
m
,
,
I
•
Oct'Nov Dec Jan Feb"Mar'tS~'AP19MaYJUnTJul Aug Sep O¢{ Nov' ?1985? f
t
f
?
~
f
Fig. 3. Mean number of ticks per species and stages collected w i t h the dragging forested area. ? indicates sampling dates.
technique in the
registered in the m a x i m u m RHs for both areas. The cycles of A. neumanni and A. cajennense are presented in Fig. 5. They are based on the presence, absence and abundance of larvae, nymphs and adults on cattle and on vegetation. For this purpose, the larval infestations of October 1985 and 1986 were considered as a combination of both species. The abundance of larvae, nymphs and adults of A. cajennense was sequential, whereas all stages ofA. neumanni were more abundant from May to July. differences were
DISCUSSION The climate was characterized by the concentration of rainfall in summer, therefore the peak infestation with B. microplus was expected to occur in aut u m n as a result of suitable conditions of temperature and humidity for egg development in the previous season (Guglielmone et al., 1981). Nevertheless, the highest tick burden was found in November 1986 when the dryness of the preceding months was supposed to affect the egg development and survival of unfed larvae of B. microplus (Wilkinson, 1970). This peak of B. microplus in spring was also recorded in two other areas of northwest Argentina (Gugliel-
98
A.A.GUGLIELMONEET AI,.
@a
0~8@@0000
RELATIVE HUMIDITY
Fig. 4. Climatic parameters values.
-100 @E,
@OQOb
-80 -60
registered
%
in the open ( 0 ) and forested
(0 ) areas. 0 1coincidental
mone et al., 1981; Mangold et al., 1987). Poor nutrition of cattle during the dry season weakens their resistance to B. microplus (Sutherst et al., 1983); this, in conjunction with the increase in the stocking rate around watering places, could be responsible for the peak of infestation during the spring. These factors may help to overcome the negative impact of the climate on the population dynamics of B. microplus, increasing the chances of the larvae finding and surviving on a host. All parasitic stages of A. neumanni and A. cajennense and adults of A. paruum were found on cattle. This agrees with a previous report which suggests that cattle are able to maintain the life cycle of the first two species of Amblyomma in the environment, but not A. parvum (Guglielmone and Hadani, 1982). The absence of all the stages of A. neumanni from January to March, followed afterwards by their simultaneous abundance (Fig. 5 ) , indicates a trien-
ECOLOGICAL ASPECTS OF TICKS, NORTHWEST ARGENTINA
99
\ _/Nymps
Fig. 5. N a t u r a l cycles of A. neumanni (A.n) a n d A. cajennense (A.c) ( [E, presence; [], a b u n d a n c e ).
nial life cycle regulated via summer diapause. This phenomenon tends to solve problems of adaptation of various arthropods (Masaki, 1980). The seasonality ofA. neumanni may be aimed at minimizing the competition with adults of A. cajennense for the same hosts. The sequential abundance of the different instars of A. cajennense indicates that there is probably one generation per year. The abundance of adults in the hottest months and of larvae and nymphs during the dry season is coincident with various observations in America and the Caribbean region (Aragao, 1936; Fairchild et al., 1966; Smith, 1975; Guglielmone and Hadani, 1982; Mangold et al., 1987 ). The lower density of ticks in the open area than in the forested area could be related to higher temperatures in the former (Fig. 4); this shortens the longevity of ticks due to dehydration (Lees, 1946) or to high metabolic rate (Tukahirwa, 1976). Host preference for the forested habitat could be another important factor regulating tick populations on the ground cover vegetation, however this was not investigated. The results of this study indicate that it could be feasible to simultaneously reduce the peak burden of all the stages ofA. neumanni, the larval population of A. cajennense and the autumn generation of B. microplus with chemical treatments of cattle between late autumn and early winter. This measure will probably affect the population of the next instars of A. cajennense, and the next generations ofA. neumanni and B. microplus. However, the host range of A. neumanni and A. cajennense is wide (Ivancovich, 1973; Guglielmone and
100
A.A.GUGLIELMONEET AI,.
Hadani, 1981 ). Therefore a quantitative evaluation of the role of other mamreals in supporting both species of Amblyomma is required to develop a sound strategy of tick control based on treatment of cattle with acaricides. Tick-resistant cattle (Bos taurus × Bos indicus ) are useful to control B. microplus (Sutherst and Utech, 1981 ) and some species ofAmblyomma (Bonsma, 1944; Strother et al., 1974). However their resistance to A. cajennense and A. neumanni has not been evaluated. This warrants further investigation since tick-resistant cattle are a better alternative to control ticks because they will delay the appearance of tick populations resistant to chemicals, a feature that sooner or later arises with the use of non-biological pesticides. ACKNOWLEDGEMENTS
We acknowledge the secretarial contribution of Ms. M.R. Fuke and the critical revision of the manuscript by Dr. E.J.A. Spath.
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and Brahman×Hereford crossbreed cattle to the lone star tick, Amblyomma americanum (Acarina: Ixodidae). J. Med. Entomol., 11: 559-563. Sutherst, R.W. and Utech, K.B.W., 1981. Controlling livestock parasites with host resistance. In: D. Pimentel (Editor), CRC Handbook of Pest Management in Agriculture. Vol. II. CRC Press, Boca Raton, FL, pp. 384-409. Sutherst, R.W., Kerr, J.D., Maywald, G.F. and Stegeman, D.A., 1983. The effect of season and nutrition on the resistance of cattle to the tick Boophilus microplus. Aust. J. Agric. Res., 34: 329-339. Tukahirwa, E.M., 1976. The effects of temperature and relative humidity on the development of Rhipicephalus appendiculatus Neumann (Acarina, Ixodidae). Bull. Entomol. Res., 66:301 312. Wharton, R.H. and Utech, K.B.W., 1970. The relation between engorgement and dropping of Boophilus microplus (Canestrini) (Ixodidae) to the assessment of tick numbers on cattle. J. Aust. Entomol. Soc., 9: 171-182. Wilkinson, P.R., 1970. Factors affecting the distribution and abundance of the cattle tick in Aus~ tralia. Observations and hypotheses. Acarologia, 12: 492-508.
