Initial frequency of alleles for resistance to Bacillus thuringiensis toxins in field populations of Heliothis virescens

Abstract

The risk of rapid pest adaptation to an insecticide is highly dependent on the initial frequency of resistance alleles in field populations. Because we have lacked empirical estimates of these frequencies, population-genetic models of resistance evolution have relied on a wide range of theoretical estimates. The recent commercialization of genetically engineered cotton that constitutively produces an insecticidal protein derived from the biocontrol agent, Bacillus thuringiensis (Bt) has raised concern that we lack data needed to quantify the risk of insect pests such as Heliothis virescens rapidly adapting to this ecologically valuable class of toxins. By individually mating over 2,000 male H. virescens moths collected in four states to females of a Bt toxin-resistant laboratory strain, and screening F 1 and F 2 offspring for tolerance of the toxic protein, we were able to directly estimate the field frequency of alleles for resistance as 1.5 ؋ 10 ؊3 . This high initial frequency underscores the need for caution in deploying transgenic cotton to control insect pests. Our single-pair mating technique greatly increases the efficiency of detecting recessive resistance alleles. Because alleles that decrease target site sensitivity to Bt toxins and other insecticides are often recessive, this technique could be useful in estimating resistance allele frequencies in other insects exposed to transgenic insecticidal crops or conventional insecticides.

Frequency and fitness cost of resistance to Bacillus thuringiensis in Chrysomela tremulae (Coleoptera: Chrysomelidae)

“…Frequencies of Bt resistance alleles as high as those reported here in C. tremulae have been reported in lepidopteran pest species such as H. virescens (Gould et al, 1997), P. xylostella (Tabashnik et al, 1997) and P. gossypiella (Tabashnik et al, 2000). The frequencies in these insects may have been high because of previous selection for resistance.…”

“…Frequentist statistics can be used on these data (Gould et al, 1997), but Bayesian methods have the advantage of explicitly taking into account sample size. Bayesian statistics have several additional advantages over frequentist statistics for resistance.…”

“…Among these factors, the frequency is certainly one of the most important: the lower the frequency, the more sustainable the strategy. The initial frequency of resistance has been estimated in only a limited number of cases, mostly in lepidopteran pests, due to practical limitations: Helicoverpa armigera (Wu et al, 2002), Heliothis virescens (Gould et al, 1997) and H. zea (Burd et al, 2003) on cotton, Ostrinia nubilalis on maize Bourguet et al, 2003), Scirpophaga incertulas (Bentur et al, 2000) on rice, and Pectinophora gossypiella (Tabashnik et al, 2000) on cotton. These studies yielded contrasting results, with the frequency of Bt resistance alleles ranging from 10 À4 to 10 À1 .…”

Fitness costs of key point mutations that underlie acaricide target‐site resistance in the two‐spotted spider miteTetranychus urticae

“…In light of this theory, the study of the potential biological weaknesses that are associated with acaricide/insecticide resistance in populations is of high importance in the context of Insecticide Resistance Management (IRM; Crow, 1957; Georghiou & Taylor, 1977). The origin and history of the nucleotide polymorphisms associated with resistance remains largely unknown (but see Gould et al., 1997; Hartley et al., 2006), which lowers the reliability of a priori predictions of potential fitness costs. In this study, we took advantage of a collection of near‐isogenic lines to quantify potential pleiotropic fitness effects of five key mutations associated with resistance in T. urticae .…”

Sequence variation in the cadherin gene of Ostrinia nubilalis: a tool for field monitoring

“…To manage resistance effectively, it is necessary to understand the genetic mechanisms of resistance (Gould and Tabasnnik, 1998;Caprio et al, 2000) and monitor insect pests of transgenic-insecticidal cultivars for changes in their tolerances of Bt toxins (Gould et al, 1997;Andow and Alstad, 1998). To do this, it is necessary to track the evolutionary changes of resistance alleles in pest populations.…”