|Hernandez, Ruben - INIFAP-SAGAR, MEXICO|
|Wagner, G - TEXAS A & M UNIVERSITY|
Submitted to: Insect Biochemistry and Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 20, 2001
Publication Date: November 9, 2001
Citation: HERNANDEZ, R., GUERRERO, F., GEORGE, J.E., WAGNER, G.G. ALLELE FREQUENCY AND GENE EXPRESSION OF A PUTATIVE CARBOXYLESTERASE-ENCODING GENE IN A PYRETHROID RESISTANT STRAIN OF THE TICK BOOPHILUS MICROPLUS. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY. v. 32. p. 1009-1016. Interpretive Summary: The Southern cattle tick, Boophilus microplus, is a carrier of several diseases of livestock and is capable of causing severe economic losses to cattle producers. Several strains of this tick have been found to possess acaricide resistance. Esterases are a family of enzymes found in numerous organisms, including insects and ticks, that are essential to numerous metabolic processes and are often involved in the development of pesticide resistance. Experimental evidence indicates that esterases are a likely cause of the development of pyrethroid resistance in a Mexican strain of B. microplus designated Cz. A specific member of the tick esterase family in the Cz strain, Cz Est9, has been found to be very active and our experiments with DNA and RNA from the Cz strain have shown that the Cz Est9 gene appears to produce more of the mRNA coding for the Cz Est9 enzyme compared to a susceptible reference strain. It is likely that the pyrethroid resistance of the Cz strain is due to the overproduction of Cz Est9. A mutation in the Est9 gene was also discovered and a DNA assay developed to detect the presence of the mutation in individual tick larvae. This mutation was especially prevalent in the resistant Cz strain compared to strains which were not resistant to pyrethroids
Technical Abstract: We utilized RNA Northern blot analysis and ribonuclease protection assays (RPA) to study the mRNA expression level of a putative carboxylesterase- encoding gene from several strains of Boophilus microplus (Canestrini). Both the Northern analysis and RPAs indicated that the esterase transcript was overexpressed in the pyrethroid resistant strain, Coatzacoalcos (Cz), compared to a susceptible control strain and a resistant strain whose pyrethroid resistance is mediated through a target site insensitivity mechanism. A PCR-based assay was designed to identify the presence of a previously reported point mutation in this B. microplus esterase gene. The reported G to A nucleotide substitution creates an EcoR I site in the mutan allele which can be detected by EcoR I digestion of the amplification products. The PCR assays showed the frequency of the mutant allele was highest in the Cz resistant strain which has been shown to have an esterase-mediated resistance mechanism. The PCR assay can be performed either on individual tick larvae or hemolymph from adults.