Linkage of acetylcholinesterase insensitivity to methyl parathion resistance inHeliothis virescens

Abstract

Resistance to methyl parathion insecticide has evolved in the tobacco budworm, Heliothis virescens, and several biochemical mechanisms have been identified in various strains. Reduced sensitivity of acetylcholinesterase to inhibition by methyl paraoxon, the active metabolite of the insecticide, is controlled by a single autosomal locus, AceIn. We report that AceIn is genetically linked to methyl parathion resistance, which is expressed as a dominant gene. Methyl parathion-resistant and -susceptible strains were intercrossed and the resulting mixed colony was heterozygous at AceIn. Pair matings from the mixed colony were chosen, on the basis of AceIn genotype only, to establish strains Ace-S and Ace-R, homozygous for AceInSS and AceInRR, respectively. The Ace-R strain was 15.9-fold resistant compared to AceInSS, while hybrid progeny expressed 24.6-fold resistance, demonstrating dominant inheritance of resistance. When progeny of the backcross (Ace-S x Ace-R) to Ace-S were exposed to a discriminating dose of methyl parathion, 24.5% survived as predicted by the model of a single resistance gene. Survivors displayed only the AceInRS genotype, demonstrating a linkage disequilibrium which was highly significant. Assuming that no other resistance genes are linked closely to AceIn, it would appear that AceIn is a powerful gene for resistance, conferring a resistance proportional to the slower rate of inhibition in the resistant enzyme. The contribution of AceIn to resistance relative to detoxicative genes and the possible interaction of resistance genes are discussed.

Resistance to insecticides in Heliothine Lepidoptera: a global view

“…A large number of reports have shown that resistance to OPs in H. virescens may be due, at least in part, to a target-site resistance involving decreased sensitivity of acetylcholinesterase to inhibition (Brown & Bryson 1992;Brown et al 1996a;Harold & Ottea 1997). In resistant strains of H. virescens, Brown & Bryson (1992) and Gilbert et al (1996) demonstrated the presence of acetylcholinesterase insensitive to inhibition by methyl paraoxon and G. Zhao et al (1996) demonstrated acetylcholinesterase insensitive to paraoxon. Although this mechanism may be common in OP-resistant insects it may not be universal within ¢eld populations of H. virescens, as shown by Harold & Ottea (1997).…”

Surveillance of Resistant Acetylcholinesterase in Heliothis virescens

“…On the other hand, our Woodrow, SC 1983 colony possessed 86.2% Aceln-R allele after prolonged colonization. There was no decline in this allele when mixed with the Aceln-S and reared for seven generations (25). Also, there is no deficit in the biochemical activity of the resistant acetylcholinesterase (20).…”

“…Decline of Aceln-R. Resistance by this mechanism is completely dominant in inheritance; i.e. heterozygous individuals are fully resistant (25). This means that susceptible alleles can be carried by heterozygous survivors and that it would be unlikely for Aceln-R to reach fixation.…”

“…While there may be two or three Aceln-S alleles, they are all equally susceptible to propoxur, but differ in the level of resistance to monocrotophos. In our laboratory strain, there was less variability of response and no clear indication of multiple Aceln-S alleles (25). Antiresistance Strategy.…”

A single gene (yes) controls pigmentation of eyes and scales in Heliothis virescens

“…Genetic transformation of insects may lead to control or reduced pest status of species destructive of food and fiber (DeVault et al, 1996). A transgenic system for Heliothis virescens is needed to explore genetic control or to unravel the complexities of insecticide resistance, a phenomenon for which this pest is among the most notorious in agriculture (Brown, 1996). Organophosphorus insecticide resistance in this species has been associated with the gene AceIn (Brown and Bryson, 1992) which was genetically linked to methyl parathion resistance (Gilbert et al, 1996) and is located on chromosome 2 (Heckel et al, 1998).…”