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

Abstract

The 'high dose-refuge' (HDR) strategy is commonly recommended and currently used for delaying or preventing pest adaptation to transgenic plants producing Bacillus thuringiensis (Bt) toxins. The efficiency of this strategy depends, among other factors, on the initial frequency of Bt resistance alleles and on the fitness costs associated with these alleles. Two years ago, an allele conferring resistance to Bt poplar was detected in a French population of the poplar pest Chrysomela tremulae F. Although this pest had never been subjected to Bt selection pressure due to human activities, the frequency of this allele was estimated at 0.0037, with a 95% credible (CI) interval of 0.00045-0.0080. We investigated the frequency of this allele in a second sample of C. tremulae collected more than 500 km from the site of the initial population. The estimated frequency in this sample was 0.0113 (95% CI 0.0031-0.0247), reinforcing the conclusion that resistance to Bt plants may be present at detectable frequencies in pest populations before selection resulting from pest management by humans. The frequency of the Bt resistance allele over the two samples was 0.0049 (95% CI 0.0020-0.0091). We also followed five laboratory lines in which the frequency of this allele was initially fixed at 0.500. After five generations maintained on non-Bt poplar leaves, the frequency of this allele decreased in all lines, whereas allelic frequencies at a neutral locus were unaffected. Thus, the Bt resistance allele detected in French populations of C. tremulae is probably associated with a fitness cost.

Detection of an Allele Conferring Resistance to Bacillus sphaericus Binary Toxin in Culex quinquefasciatus Populations by Molecular Screening

“…Novel approaches are needed to provide information for the management of resistance to bacterial toxins. The knowledge of the initial frequency of resistance alleles in field populations, particularly for those that are inherited recessively, is essential to establish strategies to delay resistance (14,36,37). In such cases, heterozygous individuals that emerge gradually in the population under selection cannot be identified by bioassays and resistance allele frequency can increase without being detected.…”

Frequency of resistance to Vip3Aa20 toxin from Bacillus thuringiensis in Spodoptera frugiperda (Lepidoptera: Noctuidae) populations in Brazil

“…Theoretically, 1/16 of F 2 larvae will be resistant homozygous (RR genotype) in isofemale lines whose parents had the resistance allele . The F 2 screen method was used to estimate the resistance allele frequency to Bt toxins in several pest species, such as Heliothis virescens (F.) (Gould et al, 1997), Pectinophora gossypiella (Saunders) (Tabashnik et al, 2000), Diatraea saccharalis (F.) , Ostrinia nubilalis (Hübner) (Andow et al, , 2000Bourguet et al, 2003;Stodola et al, 2006;Engels et al, 2010;Siegfried et al, 2014), Plutella xylostella (L.) (Zhao et al, 2002), Helicoverpa armigera (Hübner) (Liu et al, 2008;Xu et al, 2009;Mahon et al, 2010Mahon et al, , 2012, Helicoverpa punctigera (Wallengren) (Mahon et al, 2012) and Crysomela tremulae F. (Wenes et al, 2006). The resistance allele frequency in these studies ranged from 0.0009 to 0.0297.…”

Extended monitoring of resistance to Bacillus thuringiensis Cry1Ab maize in Diatraea saccharalis (Lepidoptera

“…5 The 95% confidence interval of the estimated resistance frequency was also calculated as described by Andow and Alstad. 34 The probability that a resistance allele could be identified in a family line was estimated according to the methods described in Stodola and Andow.…”