One gene in diamondback moth confers resistance to fourBacillus thuringiensis toxins

Abstract

Environmentally benign insecticides derived from the soil bacterium Bacillus thuringiensis (Bt) are the most widely used biopesticides, but their success will be short-lived if pests quickly adapt to them. The risk of evolution of resistance by pests has increased, because transgenic crops producing insecticidal proteins from Bt are being grown commercially. Efforts to delay resistance with two or more Bt toxins assume that independent mutations are required to counter each toxin. Moreover, it generally is assumed that resistance alleles are rare in susceptible populations. We tested these assumptions by conducting single-pair crosses with diamondback moth (Plutella xylostella), the first insect known to have evolved resistance to Bt in open field populations. An autosomal recessive gene conferred extremely high resistance to four Bt toxins (Cry1Aa, Cry1Ab, Cry1Ac, and Cry1F). The finding that 21% of the individuals from a susceptible strain were heterozygous for the multiple-toxin resistance gene implies that the resistance allele frequency was 10 times higher than the most widely cited estimate of the upper limit for the initial frequency of resistance alleles in susceptible populations. These findings suggest that pests may evolve resistance to some groups of toxins much faster than previously expected.

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.…”

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

“…Aminopeptidase was implicated as a major midgut receptor (Knight et al, 1994;Gill et al, 1995), followed by cadherin (Vadlamudi et al, 1995). Screening P. xylostella for survival on Cry1A and Cry1F toxins suggested cross resistance was imparted by a single gene (Tabashnik et al, 1997). This was corroborated when a major autosomal locus inherited as a recessive trait was identified (Heckel et al, 1999).…”

Insecticide Resistance and Vector Control

“…Resistance to B. thuringiensis has resulted from reduced binding of the toxin to the brush border in the lumen of the insect gut (49,50) or by enhanced digestion of toxin by gut proteases (51). The six different toxin types in the B. thuringiensis israelensis strain used for vector control were expected to retard or prevent development of a comprehensive resistance mechanism; however, multitoxin resistance to B. T. israelensis has already appeared (52,53).…”