Insect Biochemistry and Molecular Biology 30 2000 969–977 www.elsevier.comlocateibmb
Identification of a point mutation in an esterase gene in different populations of the southern cattle tick, Boophilus microplus
Ruben Hernandez
a, b
, Haiqi He
c
, Andrew C. Chen
c
, Suryakant D. Waghela
a
, G. Wayne Ivie
c
, John E. George
d
, G. Gale Wagner
a,
a
Department of Veterinary Pathobiology, College of Veterinary Medicine, Texas AM University, College Station, TX. 77843-4467, USA
b
Cenid-Parasitologia Veterinaria INIFAP-SAGAR, Apartado Postal 206 Civac, Morelos, CP 62500, Mexico
c
Food Animal Protection Research Laboratory, USDA-ARS, 2881 FB Road, College Station, TX 77845, USA
d
Knipling-Bushland US Livestock Insects Research Laboratory, USDA-ARS, 2700 Fredericksburg Road, Kerrville, TX 78028, USA Received 13 October 1999; received in revised form 28 February 2000; accepted 6 March 2000
Abstract
Two esterase cDNA sequences were obtained from susceptible and organophosphorus resistant strains of Boophilus microplus. Both sequences have a high degree of homology to carboxylesterase B. One gene has identical sequences in both strains and the
other showed two point mutations. One mutation produces an amino acid substitution when the amino acid sequence is deduced, this mutation was detected in six different populations susceptible and resistant to insecticides, but a pyrethroid resistant strain was
the only one that showed only the mutant allele. Identification of this mutation and the strong signal detected in southern blot with this strain, suggest that esterases are contributing to detoxification of pyrethroid compounds, as a resistant mechanism in Mexican
strains of the southern cattle tick.
2000 Elsevier Science Ltd. All rights reserved.
Keywords: Boophilus microplus; Esterases; Point mutation; Pyrethroid resistance; Southern blot
1. Introduction
The southern cattle tick, Boophilus microplus, is present in tropical and subtropical regions throughout the
world. This tick species is detrimental to the cattle indus- try, not only because of its direct effect on production,
but also its ability to transmit highly virulent hemoparas- ites such as Babesia spp. and Anaplasma marginale. In
recent years the control of this tick has become difficult because of the development of resistance to the acari-
cides used for its control Nolan and Schnitzerling, 1986.
In many arthropod pests, resistance to pesticides has been attributed to an increase in pesticide degrading
enzyme activity. However, in most cases it is not known whether this arises from mutant enzymes or from the
Corresponding author. Tel.: +
1-409-845-4275; fax: +
1-409-862- 2344.
E-mail address: gwagnercvm.tamu.edu G. Gale Wagner.
0965-174800 - see front matter
2000 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 5 - 1 7 4 8 0 0 0 0 0 6 9 - 2
increased production of an enzyme already present in susceptible insects Field et al., 1988.
Most insecticides in use today are esters of substituted phosphoric, carbamic or cyclopropanecarboxilic acids,
and are consequently subject to degradation by esterases Devonshire, 1991. The massive overproduction of any
esterase by insects may result in the increased detox- ification of insecticide esters first by sequestration and
then by hydrolysis when the inhibited esterase reactiv- ates Devonshire and Field, 1991. Increased hydrolysis
of insecticides by esterases has been implicated in insec- ticide resistance in many species. Recently, a carboxyle-
sterase with a single amino acid substitution was shown to contribute significantly to organophosphorus OP
resistance in blowflies Newcomb et al., 1997. Also in both the mosquito Culex quinquefasciatus Mouches et
al., 1986 and the aphid Myzus persicae Field et al., 1988, amplification of esterase genes is related with
increased detoxification of insecticides. Rosario-Cruz et al. 1997 found that an OP resistant strain of B.
microplus contained several different proteins showing increased relative amounts as well as increased esterase
970 R. Hernandez et al. Insect Biochemistry and Molecular Biology 30 2000 969–977
activity when compared with a susceptible strain. Simi- larly, pyrethroid-hydrolyzing esterases have also been
detected in B. microplus De Jersey et al., 1985. In this study we report the complete cDNA sequences
of two esterases from B. microplus, a point mutation in one sequence, and the differences among susceptible and
resistant strains in Southern hybridization.
2. Materials and methods
