Insect resistance to Bacillus thuringiensis: uniform or diverse?

Abstract

Resistance to the insecticidal proteins produced by the soil bacterium Bacillus thuringiensis (Bt) has been documented in more than a dozen species of insect. Nearly all of these cases have been produced primarily by selection in the laboratory, but one pest, the diamondback moth (Plutella xylostella), has evolved resistance in open-¢eld populations. Insect resistance to Bt has immediate and widespread signi¢cance because of increasing reliance on Bt toxins in genetically engineered crops and conventional sprays. Furthermore, intense interest in Bt provides an opportunity to examine the extent to which evolutionary pathways to resistance vary among and within species of insect. One mode of resistance to Bt is characterized by more than 500-fold resistance to at least one Cry1A toxin, recessive inheritance, little or no cross-resistance to Cry1C, and reduced binding of at least one Cry1A toxin. Analysis of resistance to Bt in the diamondback moth and two other species of moths suggests that although this particular mode of resistance may be the most common, it is not the only means by which insects can attain resistance to Bt.

Common, but Complex, Mode of Resistance of Plutella xylostella to Bacillus thuringiensis Toxins Cry1Ab and Cry1Ac

“…It is not unreasonable to suppose that a similar situation will exist with B. thuringiensis-resistant insects. The mode 1 resistance mechanism proposed by Tabashnik et al (35) could be due to a single mutation affecting toxin binding to its receptor. In a B. thuringiensis-resistant population of H. virescens, a transposon insertion into the cadherin-like receptor is believed to be responsible for the resistance phenotype (9).…”

“…Tabashnik et al (35) defined a "mode 1" form of resistance in P. xylostella in which there is loss of binding of a Cry1A toxin, no cross-resistance to Cry1Ca, and a recessive inheritance of the phenotype. Although Cry1Ab-SEL and Cry1Ac-SEL meet the first two criteria (Cry1Ab binding is also reduced in Cry1Ac-Sel [unpublished data]), their resistance to Cry1Ab and Cry1Ac, respectively, cannot be classified as mode 1 since it is inherited as an incompletely dominant trait.…”

Bacillus thuringiensis resistance in Plutella — too many trees?

“…By far, the most common resistance phenotype is known as "mode 1" in which the insect shows resistance to several Cry1A but not to Cry1C or Cry2A toxins [2], it is this phenotype that will be discussed here. Since the first Bt-resistant insects were identified much research effort has been expended in the search for the underlying genetic, physiological and biochemical mechanisms [3].…”

Genetic hitchhiking and resistance evolution to transgenic Bt toxins: insights from the African stalk borer Busseola fusca (Noctuidae)

“…The nature and uniformity of the genetic bases of resistance to Bt toxins are thus crucial aspects influencing resistance evolution and management (e.g., Tabashnik et al, 1998). Multiple recessive mutations that cause resistance to Cry1A toxins in Lepidoptera have been reported (see Heckel et al, 2007) in genes encoding Cadherin-like proteins (e.g., Morin et al, 2003) and ABC transporters (e.g., Baxter et al, 2011).…”