Tropical Pest Management 30(3): 296-301 © Crown copyright, 1984 Patterns of Resistance in Five Samples of Ethion­ Resistant Cattle Tick (Boophilus microplus) From New Caledonia L. O. Brun, J. T. Wilson* and J. Nolan* Office de la Recherche Scientifique et Technique Outre-Mer (ORSTOM), Centre de Noumee, B. P. A5, Noumee Cedex, New Caledonia. Abstract. The responses of five samples of the cattle tick Boophilus microplus (Canestrini) from New Caledonia to two carbamate and five organophosphate chemicals were determined by laboratory dosage-mortality tests on 2-3-week-old unfed larvae. Data show that acaricide resistance in New Caledonia has some similarities to the pattern of response exhibited by the Ridgelands, Mackay or Tully strains in Australia. Other registered acaricides are reviewed and alternative ways of tick management are considered. Introduction The development of strains of cattle ticks that are resistant to chemicals has been a recurring phenomenon for over 40 years, not only in Australia and South America, where Boophilus microplus (Canestrini) occurs, but also in Africa where Boophilus decoloratus (Koch) is the usual one-host cattle tick (Wharton and Roulston, 1970). In these three areas, resistance has appeared in succession to arsenic, DDT and organophosphorus (OP) compounds. In New Caledonia, arsenic and DDT were used before the introduction of ethion, the only OP compound used for cattle tick control. Following seven years use of ethion, a recent survey has demonstrated the appearance of a moderate level of resistance along the east coast and in one area of the west coast (Brun et al., 1983). In Australia, where OP acaricides have been widely used since 1956, nine resistant strains have been recognised; each is distinct toxicologically and biochemically (Roulston et al., 1977). In this paper, data are presented on the response pattern of five samples of ethion-resistant cattle ticks to seven pesticides commonly used in Australia to characterise resistant strains. Materials and methods Engorged female B. microplus were collected from cattle in five localities. Four samples came from farms on the east coast (at Thio (1), Thio (2), Nakety and Moneo) where the highest level of resistance to ethion was detected (Brun et al., 1983). The fifth sample (Pova}. came from a property located in the only area of the west coast where resistance to ethion was higher than two-fold. At the time of collection, ticks were placed in plastic containers, on layers of wet absorbent paper to avoid desiccation. These containers were usually placed in an insulated box with a small piece of ice to protect ticks from excessive heat during transport from the field to the laboratory. The ticks were incubated at 27 ± 1°C and 85-95% r.h., and their eggs hatched in about 28 days. The FAO-recommended dosage-mortality technique (Anon., 1971) for detecting and measuring acaricide resistance, modified from the Stone and Haydock (1962) method, was used. Whatman® No. 1 filter paper was impregnated with different concentrations of a particular chemical dissolved in olive oil-trichlorethylene (1:2 vol.zvol.l. The dried papers were folded to form packets into each of which 100-200 unfed 2-3-week-old larvae were released. These packets were then kept in the incubator. Mortality was recorded after 24 h of exposure. Impregnated papers were prepared in Long Pocket Laboratories, CSI RO, Brisbane, and dispatched by airmail to ORSTOM Centre, Noumea. 'CSIRO, Division of Tropical Animal Science, Long Pocket Laboratories, Private Bag No. 3, Indooroopilly, Queensland 4068, Australia. • Resistance to acaricides - Brun et al. 299 0.001 0.01 1.0 0.01 0.1 1.0 10 , , • CARBARYL , B 15 'f 10 ,1 1 50 1 • zo " 0 1 . 5 0 .'1 () ' , 1 PROMACYL COUMAPHOS , 1 • 1 115 , " 1 10 l' Y",<II.' 0 , ' " /0 Â,' >- 5 ./9 ... 1 • cr: ...ca ~ 0 1 CHLORPYRIFOS DIOXATHION 1 :E • ,Y 15 1 10 *- 1 50 1 ,1 zo , • 1 5 • ,. 1 0 1 0 1 , 1 lIll CYANOPHOS , ETHION 1 y, YI 115 1 1 1 1 1 1 ., 1 zo 1 P ,1 5 ;. , • , 0.001 0.01 0.1 1.0 0.01 0.1 1.0 10 Concentration in olive oil (%) foE.W CAlEDONIA LOCALITIES AUSTRALIAN REFERENCE STRAINS • Nakety Y Yeerongpilly (susceptible) 0 ThlO (1) R Ridgelands (reslstant) • Thio (2) M Mackay (resistanl) Fig. 2. Dosage-mortality responses of two ethion-resistant samples of Boophifus micropfus from New Caledonia, compared with Australian reference strains and one sample from New Caledonia. The survey for DDT resistance established by using a 2% DD indicates that three samples have resistant larvae: Moneo (97.5% mortality), Thio (1) (97.7%) and Poya (98.3%). The remaining two samples may be resistant but observed mortalities are too high to confirm such a hypothesis, viz Thio (2) (99.8%) and Nakety (99.8%). As mentioned by Stone (1962) the gene for DDT resistance is incompletely recessive and this discriminating dose may have detected only homozygous individuals. The frequency of DDT-resistant individuals in the five New Caledonian samples was low. A recent survey showed that a similar situation existed in Australia (Roulston et al., 1981) where more than 90% of DDT-resistant samples produced progeny with less than 10% resistant individuals. The small number of survivors at DD (2-3%) as found in three out of five of our samples shows that DDT-resistant ticks are still present in field populations despite the fact that DDT has not been used for tick control in New Caledonia since 1973. A very slow rate of reversion has also been documented in Australia, where DDT-resiuance in the field is present after about 20 years ' non-use of DDT, and this concerns at least 8% of tick-infested properties in Queensland (Roulston et al., 1981). The presence of DDT-resistant strains in several places on the island has caused some concern • Resistance to acaricides - Brun et al. 297 The following chemicals were used in their technical form: carbaryl* (1-naphthyl methylcarbamate), chlorpyrifost (diethyl 3, 5, 6-trichloro-2-pyridyl phosphorothionate), coumaphos* (3-chloro-4-methyl-7-coumarinyl diethyl phosphorothionate), cyanophost (4-cyanophenyl dimethyl phosphorothionate), diazinon* (diethyl 2­ isopropyl-6-methyl-4-pyrimidinyl phosphorothionate), dioxathion* [(S, SI-1, 4-dioxan-2, 3-ylidene bis (0, O-diethyl phosphorothiolothionate)] , ethion * [tetraethyl S, SI -methylenebis (phosphorothiolothionate)] , promacyl * (3­ isopropyl-5-methylphenyl N-butyryl-N-methyl carbamate). ln the dosage mortality tests there were two replicates at each concentration. The following concentration ranges were used: promacyl 0.0078-1.0%, carbaryl 0.00039-0.1%, chlorpyrifos 0.0039-0.125%, cyanophos 0.0024-0.312%, coumaphos 0.0078-0.5%, dioxathion 0.039-5%, diazinon 0.0024-0.312%. The larvae were also monitored for resistance with a discriminating dose (DO) of ethion (0.5%) and DDT (2%). These concentrations were chosen to give 100% mortalities in susceptible ticks, but intermediate or no mortalities in resistant strains. Ethion log dose·probit (Id·p) data obtained in a previous study (Brun et al., 1983) were used for samples from Poya, Thio (1) and Thio (2). Response data of the samples tested in New Caledonia have been compared with dosage-mortality lines of an Australian susceptible reference strain (Yeerongpilly) and resistant strains (Tully, Ridgelands, Mackay and Biarra). The susceptible reference strain has been cultured continuously by CSI Ra since 1948 without contact with acaricides. The resistant strains are homogeneous populations which have been selected from heterogeneous field samples found to contain a new type of resistance. They have been developed separately by selecting each generation of larvae with an appropriate chemical for 24 h to kill the less resistant of the population before applying them to an animal. Selection is maintained until the larvae give a homogeneous response. Results and discussion The responses of Poya, Moneo and Thio (2) are shown in Fig. 1 and of Nakety and Thio (1) in Fig. 2. Poya, Moneo and Thio (2) are almost homogeneous and straight Id-p lines, fitted by eye, have been drawn. Their resistance patterns compared with the Yeerongpilly susceptible strain for various chemicals are as follows: Moneo and Poya exhibit moderate resistance to coumaphos and dioxathion but very low or no resistance to carbaryl, promacyl, diazinon, cyanophos and chlorpyrifos. Thio (2) shows higher resistance to carbaryl and dioxathion than Moneo and Poya, moderate resistance to coumaphos, diazinon, cyanophos and promacyl, but higher resistance to this last compound than Biarra (this also occurs in some Australian resistant strains). Resistance to chlorpyrifos in Thio (2) is only of low level. These responses to the chemicals used indicate some similarities between the New Caledonian samples and Australian resistant strains. Poya and Moneo have similar responses to Tully in tests with promacyl, carbaryl, coumaphos, chlorpyrifos, diazinon and cyanophos, but not to dioxathion. Thio (2) shows a similar or close response to Mackay in test with carbaryl, coumaphos and dioxathion but in tests with diazinon and cyanophos it is very close to the Ridgelands type. Its responses to promacyl and chlorpyrifos are intermediate between these Austral ian strains. Thio (2) is the most resistant of ail samples tested but apart from its response to dioxathion, a chemical which does not readilydifferentiate between Mackay, Ridgelands and Biarra, there is no indication of resistance similar to Biarra. This is particularly emphasised by the Id-p lines obtained for cyanophos and coumaphos, chemicals to which Biarra normally exhibits a very high level of resistance. Nakety and Thio (1) are heterogeneous, Thio (1) having fewer susceptible individuals than Nakety. According to the response to carbary 1 the estimated percentage of susceptibles is 15-20% in Nakety and 2-5% in Thio (1). Nakety and Thio (1) appear to be in the process of changing and their potentialities seem to be close to Thio (2).