Detection of single-base substitution in an esterase gene and its linkage to malathion resistance in the parasitoid Anisopteromalus calandrae (Hymenoptera : Pteromalidae)

Anisopteromalus calandrae (Howard) (Hymenoptera: Pteromalidae) is an import ant parasitoid of stored-grain insect pests. Partial cDNA sequences of an e sterase-like enzyme have been obtained from a malathion-pesistant (R) strai n and a susceptible (S) strain of this wasp. A single-base substitution in the R strain has been confirmed by using PGR amplification of specific alle le (PASA) to amplify genomic DNA extracted from individual resistant and su sceptible parents, F-1 hybrids from double reciprocal crosses, and progeny from backcrosses. The R allele appeared to be inherited in a strict Mendeli an fashion in both diploid female and haploid male progeny. The esterase fr agment co-segregated with resistance in these crosses and backcrosses. Fema le wasps in a mixed population of A calandrae that survived a malathion scr een carried the R allele for the esterase-like enzyme, while those wasps th at died did not have the R allele. The single base-pair mutation, guanine i n the R strain and thymine in the S strain, presumably results in a tryptop han-to-glycine amino acid substitution in the encoded protein. We do not kn ow how these amino acid substitutions may relate to functional differences in the enzyme. However, this esterase gene or another linked esterase gene may encode the resistance-associated malathion detoxifying activity in the R strain. (C) 1999 Society of Chemical Industry.