Pestic. Sci. 1917, 8, 484-486

Resistance to Synthetic Pyrethroids in a DDT-resistant Strain of BooPhilus microplus

James Nolan, William J. Roulston and R. Harry Wharton

Division of Entomology, CSIRO, Long Pocket Laboratories, Meiers Road, Indooroopitly, Queenstand @fa, Australia

(Manuscript received 28 February 1977)

The susceptibility of a standard reference strain of the cattle tick Boophilus microplus, to a group of synthetic pyrethroids, has been compared with that of a DDT-resistant strain. Cross resistance has been demonstrated in laboratory and field tests.

1. Introduction

The cattle tick Boophilus microplus (Can.) has developed resistance to a wide variety of chemicals used for its control in many areas of the world.' In Australia, where control is achieved with acaricides containing the organophosphorus, carbamate or amidine groups, it is only the amidine group that so far has been without a serious resistance problem. Consequently there is a critical need for the development of new classes of acaricides.

Synthetic pyrethroids, including several synthesised and shown to have outstanding potential as insecticides by Elliott and co-workers,z have been found to be highly effective for the control of susceptible, organophosphorus-resistant and carbamate-resistant strains of the cattle tick (Nolan unpublished). In agreement with the above workers, who found a high level of insecticidal activity associated with (S)-a-cyano-3-phenoxybenzyl (1R)-cis-3-(2,2-dibromovinyl)-2,2-dimethylcyclo- propanecarboxylate (NRDC 161), we found this compound to be one of the most active acaricides ever tested against B. microplus. However, previous reports have demonstrated a correlation between DDT resistance and resistance to natural pyrethrins in several pest species including the one-host cattle tick B. decoloratus in South Africa. 3, Hence it was important to assess the effect of a range of synthetic pyrethroids against DDT-resistant ticks to determine whether cross resistance would limit their use in tick control.

2. Experimental

2.1. Strains A homogeneously DDT-resistant strain of B. microplus has been maintained at these laboratories for many years. Larvae of this strain exhibit a 14.5 and 2.4 fold level of resistance to DDT and pyrethrum extract respectively, compared with larvae of the susceptible Yeerongpilly reference strain (Table 1).

2.2. Treatments The responses of the DDT-resistant and susceptible ticks to the various compounds were compared in the laboratory and in spraying trials on infested cattle. Larvae were enclosed in packets impreg- nated with olive oil solutions, (the recommended FA0 method for the detection of resistance in Boophilus spp.)5 and acetone solutions were applied topically to engorged females. For the spraying trials, groups of three calves in open pens were artificially infested with either DDT-resistant or susceptible ticks at the rate of 10 OOO larvae/ animal 3 times a week for 31 weeks, to ensure that at the time of treatment all stages were present. Following treatment by spraying, the percentage

484

Resistance of Boophilus microplus to pyrethroids 485

Table 1. Response of DDT-resistant and susceptible Boophilus microplus to synthetic pyrethroids, DDT and pyrethrum.

Chemical -

Permethrin (NRDC 143) 3-Phenox ybenzyl ( ? )-cis,trans-3-(2,2-dichlorovinyl)- 2,2-dimethylcyclopropanecarboxylate (cis: trans ratio 25 :75)

Cypermethrin (NRDC 149) ( 2 )-~~-Cyano-3-phenoxybenzyl ( )-ris,trons-3-(2,2-dichlorovinyl)- 2.2-dimethylcyclopropanecarboxylate (cis: trans ratio 5050)

(S)-a-Cyano-3-phenoxybenzyl ( 1 R)-cis-3-(2,2-dibromovinyl)- 2.2-dimeth ylcyclopropanecarboxylate

(-f: )-a-Cyano-3-phenoxybenzyl ( f )-2- (4-chlorophenyl)-3-methylbutyrate

( ? )-a-Cyano-3-phenoxybnzyl 2,2,3,3-tetramethylcyclopropanecarboxylate

( + ) - I -(3-Phenoxypenzyl)propyl 2,2,3.3-tetramethylcyclopropanecarboxylate

NRDC 161

Fenvalerate (S5602)

S3206

WL41517

D DT Pyrethrum extract

~~~ ~ ~~~

Engorged females Larvae ~ ~. . . -

DDT- DDT-

Susceptible strain Susceptible strain strain EDao" Resistance strain LC50 Resistance

resistant resistant

2.1 4.4

2.0 2.8

0.3 3.7

5.2 2.9

0.59 2.0

3.0 2.4

13 1.8 -b -

230 3.3

120 10

29 8.3

380 3.9

56 2.2

200 2.4 7600 14.5 320 2.4

a Dosage for 50% decrease in egg production. At 100 pg DDT/g tick response was < 20%.

Table 2. Control of susceptible and DDT-resistant Boophilus microplus by sprays of synthetic pyrethroid. DDT or pyrethrum.

Chemical

Permethrinb CypermethrinC

NRDC 161

Fenvalerate S3206 WL 41517 DDT Pyrethrum extract

Concentration (mg/litre)

250 so 250 50 250 250 250 250 5000 500

~- ~~~ ~ ~

B. microplus control" (%)

Susceptible DDT-resistant . . -. . ... . . . . . ..

strain strain

96.5(98.1) 70.2(81.3) 92.5 - 63 (65.5) 98.1 - 92.6 (96. I) 98.5 (99.4) 78.4 (85.2) 98.5 (99.5) 98.0 (99.4) 95 (96.4) 59.5 (67.4) 99.5 (99.9) 92.3 (94.5) 96.8 - 77 (82.6) 85.1 - 40 (43.4) 97.1 (97.8) 91.1 (92.4)

- . .- - . -

a Numbers in brackets are percentage tick survival figures corrected

I, Ratio cis: trans 25 :75. Ratio cis:fruns 5050.

for weight and viability of eggs produced.

486 J. Nolan el al

control was estimated from a daily comparison of the numbers of engorged females dropped, and weight of eggs produced, from the treated and untreated groups. Corrections for the differences in pretreatment counts were calculated as described previously.0

3. Results and discussion

Results in Table 1 demonstrate that resistance to all of the synthetic pyrethroids tested is present in both larvae and engorged females of the DDT-resistant strain. These results were confirmed in the spraying trials where each of the synthetic pyrethroids gave significantly lower control of DDT- resistant ticks than of susceptible strain ticks (Table 2). The more active compounds e.g. NRDC 161, although obviously affected by the resistance, still effected satisfactory control of the resistant strain at relatively low concentrations. However for compounds with lower activity, such as permethrin (NRDC 143), high concentrations would be needed in the field to achieve satisfactory levels of control of DDT-resistant ticks.

DDT resistance in B. microplus was first reported in Australia in 19557 and was shown later to be due to a single, incompletely recessive, autosomal gene.8 The prevalence of DDT resistance in tick infested areas of Australia is unknown. However, a recent preliminary survey showed that DDT- resistant ticks are still present in field populations despite the fact that DDT has not been used for tick control since 1962. Because of the presence of resistance to DDT in the field, and the cross- resistance demonstrated in this study, selection pressure by pyrethroids might lead to rapid develop- ment of resistance to these chemicals and would adversely affect control.

The mechanism of resistance to DDT in B. microplus is not known, a previous study in this laboratory having failed to find either increased metabolism or slower penetration of DDT as poss- ible mechanisms of resistance.9 This is interesting in relation to an earlier finding that cross resistance between DDT and natural pyrethrins in houseflies (Musca domestica L.) was associated with unexplained “knock-down resistance” but not with DDT resistance due to the more common dehydrochlorination mechanism.3

References

I . 2. 3. 4. 5 . 6. 7. 8. 9.

Wharton, R. H. Wld Anim. Rev., 1976, 20, 8. Elliott, M . ; Farnham, A. W.; Janes, N. F.; Needham, P. H.; Pulman, D. A. Pesfic. Sci. 1975. 6, 537. Busvine, J. R. Nature, Lond., 1951, 168, 193. Whitehead, G. B. Nafnre, Lond., 1959, 184, 378. PI. Prot. Bull. F.A.O., 1971, 19, IS. Roulston, W. J . ; Stone, B. F.; Wilson, I. T.; White, L. I. B d l . ent. Res., 1968, 58, 379. Legg, J.; Brooks, 0. H.; Joyner, C. Ausf. vet. J . , 1955, 31, 148. Stone, B. F. Ausf. J . agric. Res.. 1962, 13, 984. Schnitzerling, H. J.; Roulston, W. J.; Schuntner, C. A. Amt. J. h i d . Sci., 1970. 23, 219.