668

Isolation and Partial Characterization of the Montecitos Strain of

Boophilus microplus

(Canestrini, 1877) Multiresistant to Different Acaricides

EFRAÍN BENAVIDES,

a

JOSÉ LUIS RODRÍGUEZ,

a

AND ALVARO ROMERO

Programa Nacional de Epidemiología Veterinaria (EpiVet),Corporación Colombiana de Investigación Agropecuaria, CORPOICA-CEISA, Santafé de Bogotá, Colombia

INTRODUCTION

A primary problem for livestock production in tropical and subtropical regions ofthe world is the infestation with ticks, in particular

Boophilus microplus.

In Colom-bia, this tick is one the major constraints on the improvement of livestock productiv-ity, mainly because of the difficulty of introducing improved breeds to lowlands withthe problems of tick infestation and hemoparasitic diseases.

1

The most currentlyused method for tick control in the country is treatment with acaricides; however thispractice has started to become ineffective as a result of development of tick resis-tance.

2

Day by day, multiresistant ticks are emerging.

3

The understanding of themultiresistance phenomenon in

B. microplus

and the design of control strategiesrequires that different tick strains be maintained in the laboratory in order to charac-terize the spectrum and the mechanisms of resistance involved. In Colombia thepresence of multiresistant ticks has not yet been reported for

B. microplus.

4

MATERIALS AND METHODS

A sample of approximately 300 engorged

B. microplus

females were obtainedfrom a farm in the province of Socorro, Santander, Colombia, the owner of whichhad reported low effectiveness in tick control after using different acaricides. Tickswere transported to the laboratory to obtain the larval progeny and their resistancespectrum to acaricides was characterized. Subsequently, the strain has been repro-duced in the laboratory, feeding on confined susceptible calves in separate isolationrooms. The larval packet test (LPT) of the FAO was used as described elsewhere,

5

employing larvæ of specific age (14–21 days). The products used were representa-tive of organophosphates (OP) and synthetic pyrethroids (SP). Resistance level toamitraz was assessed by using a modified LPT, described by Kemp

et al.,

6

and by an

a

Address for correspondence: Centro de Investigación en Salud y Producción Ani-mal. CEISA. Apartado Aéreo 39144. Bogotá, Colombia. Voice: (+57-1)-3686252.

ebenavid@hemeroteca.icfes.gov.co joselrb@hotmail.com

669BENAVIDES

et al.

: MONTECITOS STRAIN OF

BOOPHILUS MICROPLUS

adult immersion test (AIT) modified from Drummond

et al.,

7

on a range of concen-trations from 0.0104

%

to 0.416

%

prepared from a commercial product.The LPT results were scored for several replicates of the isolated strain, as for the

reference susceptible Yeerongpilly strain. Results of larval mortality were then plot-ted against concentration on logarithmic probit paper.

5

The degree of resistance inthe sample was obtained by calculating the resistance factor, using as reference theLC50

%

of the susceptible reference Yeeronpilly strain.

5

RESULTS AND DISCUSSION

For the OP chlorphenvinfos, different responses were recorded for the susceptibleand resistant strains (see F

IGURE

1). For the Yeerongpilly strain, total mortality wasobserved at all concentrations exceeding 0.05

%

, The Montecitos strain produced afairly straight line, approaching 100

%

mortality only at the highest concentrations.Similar behavior was observed for all the OPs evaluated. In the case of amitraz, thereproductive efficiency of engorged ticks was inhibited to 46.7

%

when a dose tentimes that recommended for use in the field (1040 ppm) was used. T

ABLE

1 showsdata concerning the estimation of the LC

50

values and the calculation of resistancefactors (RF). Significant degrees of resistance to the OP clhorfenvinphos, couma-phos, and diazinon were observed; but the highest RF values were obtained for theSP deltamethrin and cypermethrin. The corresponding RF for amitraz exceeded 69in LPT and 15 in the AIT.

These results confirm the hypothesis that the Montecitos strain corresponds to acritical situation of multiresistance, similar to that reported previously for the Ultimo

FIGURE 1. Comparison between mortality–dose curves obtained in LPT with theorganophosphate chlorphenvinfos for the reference susceptible Yeerongpilly (YEE) strainand for the Montecitos (MON) strain. Each line represents a different replica.

670 ANNALS NEW YORK ACADEMY OF SCIENCES

strain in Australia.

2

Acaricide resistance management relies on the efficient identifi-cation and characterization of resistant strains, and attempts to develop counter mea-sures against these strains after resistance has emerged.

2

The increase of emergingresistance to newer molecules, such as amitraz, has made it more difficult to estab-lish appropriate tick control strategies. This suggests that it is important to involveall the available methodologies as part of policies of integrated parasite manage-ment, thereby attempting to delay the development of acaricide resistance.

REFERENCES

1. B

ENAVIDES

, O.E. 1993. Control integral de ecto y hemoparásitos en la ganadería bov-ina en el trópico. Rev. ACOVEZ

17

(3): 5–9.2. K

UNZ

, S.E. & D.H. K

EMP

. 1994. Insecticides and acaricides: resistance and environ-mental impact. Rev. Sc. Tech. Off. Epiz.

13:

1249–1286.3. T

HULLNER

, F. 1997. Impact of pesticide resistance and network for global pesticideresistance management based on a regional structure. Revista Mundial de Zootecnia

89:

41–45.4. B

ENAVIDES

, E. 1995. Resistencia de artrópodos a insecticidas. Factores que favorecensu desarrollo y estrategias para combatirla. Revista ACOVEZ

20

(2): 26–33.5. F

OOD

AND

A

GRICULTURE

O

RGANIZATION

OF

THE

U

NITED

N

ATIONS

, FAO. 1984. Acari-cide Resistance Test Kit. Instructions for use. World Acaricide Resistance ReferenceCenter, WARCC.

T

ABLE

1. Resistance factors of unfed larvæ of Montecitos strain of

Boophilus microplus,

determined by comparison with the LC

50

for unselected larvæ of the referenceYeerongpilly strain

N

OTE

: LPT, larval packet test; AIT, adult immersion test;

n

, number of replicates of each test;RF, resistance factor.

Chemical Test Used

n

Yeerongpilly LC

50

%

(ppm) (95

%

CL)

n

Montecitos LC

50

%

(ppm) (95

%

CL)

RF

Cypermethrin LPT 5 156.7

(151.1–162.3)

5 8894.5

(5965.7–11823.3)

56.74

Deltamethrin LPT 5 33.1

(15.9–50.3)

5 12309.3

(6710.1–17908.7)

371.7

Coumaphos LPT 5 101.6

(76.8–126.3)

1 2031.5 19.99

Clhorfenvinphos LPT 5 188.6

(148.5–228.8)

5 1989.1

(1504.4–2473.9)

10.54

Diazinon LPT 5 83.3

(62.2–104.5)

5 2142.8

(1383.0–2902.7)

25.7

Amitraz LPT 5 67.3

(60.4–74.2)

4 6111.9

(2677.1–9546.8)

69.99

Amitraz AIT 10 9.48518

(1.5–17.4)

10 387.17

(133.1–453.3)

15.27

671BENAVIDES

et al.

: MONTECITOS STRAIN OF

BOOPHILUS MICROPLUS

6. K

EMP

, D.H., F. T

HULLNER

, K.R. G

ALE

, A. N

ARI

& G.A. S

ABATINI

. 1998. AcaricideResistance in Boophilus microplus ticks. Report to the Animal Health Services,AGAH, FAO, October 1998.

7. D

RUMMOND

, R.O., W. G

LANDEY

, T. W

HETSTONE

& S. E

RNEST

. 1971. Laboratory test-ing of insecticides for control of the winter tick. J. Econ. Entom.

64:

686–688.