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Home , Chlorpyrifos, Cyanophos, Dioxathion, Ethion

Tropical Management 30(3): 296-301 © Crown copyright, 1984

Patterns of Resistance in Five Samples of ­ 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 and five chemicals were determined by laboratory dosage-mortality tests on 2-3-week-old unfed larvae. Data show that resistance in New Caledonia has some similarities to the pattern of response exhibited by the Ridgelands, Mackay or Tully strains in Australia. Other registered 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 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

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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), * (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). Responses vary: to some chemicals they appear similar to Ridgelands but to others similar to Mackay. As both samples are heterogeneous populations, it is difficult to relate them to the homogeneous resistant strains obtained in Australia after laboratory selection with an acaricide. Both samples have the same kind of response except to coumaphos. Thio (1) is always more resistant than Nakety. Their response to coumaphos, a chemical which could differentiate Ridgelands and Mackay, indicates that Nakety is closer to the Ridgelands type. In this case, Nakety should show a higher resistance than Thio (1) to cyanophos, as did Ridgelands to Mackay in tests with this chemical. As this does not occur, Nakety would appear to be undergoing the same process as Thio (1) to a Thio (2) type of resistance, but at a much earl ier stage of development.

'Common name recommended by the International Organization for Standardization (JSO/R 1750-1970). tCommon name recommended by the British Standards Institution lBS 1831 : 1969 and supplements). 298 Tropical Pest Management Vol. 30 No. 3, September 1984

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Concentration in olive oil (%)

NEW CALEDONIA LOCALITIES AUSTRALIAN REFERENCE STRAINS

• Poya Y Yeerongpilly (susceptible) • Thlo (2) T Tully (reslstant) • Moneo R Ridgelands (resistant) M Mackay (reststant)

B Biarra (reslstant)

Fig. 1. Dosage-mortality responses of three ethion-resistant samples of Boophilus microplus from New Caledonia, compared with Australian reference strains.

This hypothesis is supported by the highest mortality level obtained in Nakety with ethion discriminating tests: Nakety (97.5%) as compared with Thio (1) (5.9%) and Thio (2) (1.3%). The other mortality data for ethion at DO are 5.3% for Moneo and 14.7 % for Poya. Those data confirmed previous studies (Brun et al., 1983) showing that among the three samples Thio (1), Thio (2) and Poya, Thio (2) contains the highest proportion of ticks resistant to ethion and Poya the least. The very low level of resistance to ethion detected in the Nakety sample is surprising as a previous survey on the east coast, where Nakety is located, showed a mortality range from 0-29.4% at DO. This may be due to the management of cattle from this wild and mountainous locality where farmers do not always muster ail their animais and practise irregular dippings. 300 Tropical Pest Management Vol. 30 No. 3, September 1984 for the future use of synthetic , as cross-resistance between this new group and DDT-resistant strains has been demonstrated from laboratory cultures in Australia (Nolan et al., 1979). DDT was still used in New Caledonia in 1973 while the use of ail chlorinated hydrocarbons for cattle tick control was banned in 1962 from the Australian market because of residues in animal products. Thus the prolonged use of DDT has delayed by 17 years the intro­ duction of OPs and the appearance of resistance to compounds of this group.

The samples were compared with the dosage-mortality responses of some Australian strains although there was no reason to believe that the OP-resistance developing in New Caledonia would follow the pattern established in Australia. Such OP acaricides as dioxathion, diazinon and coumaphos, upon which cattle tick control largely depended before and after the ad vent of OP-resistance in Queensland, have never been used in New Caledonia.

The results show some similarities between the New Caledonian samples and the Australian strains but the pattern of cross resistance does not always exist. There is evidence that OP-resistance is present but it is probably developing its own characteristics, the significance of which will not be fully appreciated until spray trials can be carried out using animais infested with the resistant populations. The New Caledonian cattle industry has the obvious advantage of being far behind the Australian in the development of resistance; several chemical groups are therefore available for the replacement of ethion. 1. Chlorpyrifos, an OP compound, is one of the few chemicals that gave adequate control of ail Australian resistant ticks before the development of the Mt. Alford strain in 1970, but being of the same group as ethion, its usefullife may not be more than a few years. 2. Promacyl, an acylated carbamate introduced in Australia in 1973, is still effective (Nolan, personal communication) and provides 95% control of the Mackay and Tully strains (Wharton and Roulston, 1977).

3. , a triazapentadiene, gives excellent control (over 99%) of ail OP-resistant strains in Australia (Wharton and Roulston, 1977). 4. Pyrethroids provide excellent control of cattle tick at very low concentrations but the presence of DDT-resistant strains in New Caledonia requires that the concentration chosen is high enough to control the most resistant strains to avoid or delay the development of resistance. The use of OPs to potentiate pyrethroids should be considered (Nolan and Bird, 1977) in order to reduce concentration and the expense of dipping.

With these chemicals the New Caledonian cattle industry should be able to rely on chemical control for 10-20 years, but it should be of first priority to use the coming decades to develop alternative methods of control that are less dependent on acaricides. Apart from the use of resistant cattle there is no known biological or genetic control that would be effective against ticks (Anon., 1975). In Australia the spread of resistance and the introduction of more costly acaricides increased the chemical market by three and a half times between 1970 and 1978. At the same time, however, the introduction of Bos indicus blood strain into Australian beef herds has been encouraged (Eider et al., 1979). This change in cattle management, involving less dipping by graziers, is the main reason for a fall in the chemical market from A$ 6.0 million to A$ 4.1 million from 1978 to 1983 (Wood, personal communication). As the production of beef is the primary object of the New Caledonian cattle industry the strategy of using more tick-resistant cattle should be greatly encouraged. This, especially if combined with other measures, should reduce dependence upon chemicals. A long-term government project should be established to avoid, or at least reduce, the problems experienced in Queensland.

Acknowledgements

The assistance of Miss Hannelore Butz in the preparation and packaging of the impregnated pa pers and of Mrs Suzanne Hughes in preparing the figures is gratefully acknowledged.

References

ANON. (1971). Aecommended methods for the detection and measurement of resistance of agricultural pests to pesticides. Tentative methods for larvae of cattle tick Boophilus spp. FAO method No. 7. FAO Plant Protection Bulletin 19: 15-18. ANON. (1975). Cattle tick in Australia - inquiry by the Cattle Tick Control Commission. Australian Government Publishing Service, Canberra. BAUN, L. O., WILSON, J. T. and DAYNES, P. (1983). Ethion resistance in the cattle tick (Boophilus microplus) in New Caledonia. Tropical Pest Management 29 (1): 16-22. ELDEA, J, K., DUNWELL, G. H., EMMEASON, F. A., KEAANAN, J. F., WATEAS, K. S., KNOTT, S. G. and MOAAIS, A. S (1979). A survey concerning cattle tick control in Queensland. 1. Producer attitudes. pp. 35-40. In Proceedings of the 56th Annual Conference of the Australian Veterinary Association. •

Resistance to acaricides - Brun et al. 301

NOLAN, J. and BI RD. P. E. (1977). Co-toxicity of synthetic pyrethroids and organophosphorous compounds against the cattle tick (Boophilus microplus). Journal of the Australian Entomological Society 16: 252. NOLAN, J., ROULSTON, W. J. and SCHNITZERLlNG, H. J. (1979). The potential of some synthetic pyrethroids for control of the cattle tick (Boophilus microplus). Australian Veterinary Journal 55: 463-466. ROULSTON, W. J., SCHUNTNER, C. A., SCHNITZERLlNG, H. J., WI LSON, J. T. and WHARTON, R. H. (1977). Characterization of three strains of organophosphorus-resistant cattle ticks (Boophilus microplus) from Bajool. Tully and Ingham. Australian Journal of Agricultural Research 28: 345-354. ROULSTON, W. J., WHARTON, R. H., NOLAN, J., KERR, J. O., WILSON, J. T., THOMPSON, P. G. and SCHOTZ, M. (1981). A survey for resistance in cattle ticks to acaricides. Australian Veterinary Journal 57: 362-371. STON E, B. F. (1962). The inheritance of DDT resistance in the cattle tick, Boophilus microplus. Australian Journal ofAgricultural Research 13: 984-1007. STONE, B. F. and HAYDOCK, K. P. (1962). A method of measuring acaricide susceptibility of the cattle tick Boophilus microplus (Can.). Bulletin of Entomological Research 53: 563-578. WHARTON, R. H. and ROULSTON, W. J. (1970). Resistance of ticks to chemicals. Annual Review of Entomology 15: 381--404. WHARTON, R. H. and ROU LSTON , W. J. (1977). Acaricide resistance in Boophilus microplus in Australia. pp. 73-92, ln Workshop on Hemoparasites (Anaplasmosis and Babesiosisl, Cali, Colombia, 17-22 March 1975. Ed. Wells, E. A. Centro International de Agricultura Tropical, Cali, Colombia.