Responses to Bt toxin Vip3Aa by pink bollworm larvae resistant or susceptible to Cry toxins

Abstract

BACKGROUND: Transgenic crops that make insecticidal proteins from Bacillus thuringiensis (Bt) have revolutionized management of some pests. However, evolution of resistance to Bt toxins by pests diminishes the efficacy of Bt crops. Resistance to crystalline (Cry) Bt toxins has spurred adoption of crops genetically engineered to produce the Bt vegetative insecticidal protein Vip3Aa. Here we used laboratory diet bioassays to evaluate responses to Vip3Aa by pink bollworm (Pectinophora gossypiella), one of the world's most damaging pests of cotton.RESULTS: Against pink bollworm larvae susceptible to Cry toxins, Vip3Aa was less potent than Cry1Ac or Cry2Ab. Conversely, Vip3Aa was more potent than Cry1Ac or Cry2Ab against laboratory strains highly resistant to those Cry toxins. Five Crysusceptible field populations were less susceptible to Vip3Aa than a Cry-susceptible laboratory strain (APHIS-S). Relative to APHIS-S, significant resistance to Vip3Aa did not occur in strains selected in the laboratory for > 700-fold resistance to Cry1Ac or both Cry1Ac and Cry2Ab.CONCLUSIONS: Resistance to Cry1Ac and Cry2Ab did not cause strong cross-resistance to Vip3Aa in pink bollworm, which is consistent with predictions based on the lack of shared midgut receptors between these toxins and previous results from other lepidopterans. Comparison of the Bt toxin concentration in plants relative to the median lethal concentration (LC 50 ) from bioassays may be useful for estimating efficacy. The moderate potency of Vip3Aa against Cry1Ac-and Cry2Ab-resistant and susceptible pink bollworm larvae suggests that Bt cotton producing this toxin together with novel Cry toxins might be useful as one component of integrated pest management.

Global Patterns of Insect Resistance to Transgenic Bt Crops: The First 25 Years

“…We found no reports of practical resistance to Vip3Aa. Although Cry and Vip proteins share some structural similarities, they have different midgut receptors and cross-resistance between them is weak or nil (Chakroun et al 2016, Tabashnik and Carrière 2020, Byrne et al 2021, Tabashnik et al 2022).…”

Inheritance and fitness cost of laboratory-selected resistance to Vip3Aa in Helicoverpa zea (Lepidoptera: Noctuidae)

“…The Vip3Aa51 protoxin used for selection and all experiments described herein was provided by BASF (Morrisville, NC). It was produced with an Escherichia coli recombinant vector as a tagged protein (Axmi005) purified on an amylose column (Sampson et al 2008, Tabashnik et al 2022). In bioassays with Pectinophora gossypiella , the tag alone did not affect survival (Tabashnik et al 2022).…”

“…It was produced with an Escherichia coli recombinant vector as a tagged protein (Axmi005) purified on an amylose column (Sampson et al 2008, Tabashnik et al 2022). In bioassays with Pectinophora gossypiella , the tag alone did not affect survival (Tabashnik et al 2022). Because Vip3Aa51 has 97.1% amino acid sequence similarity to Vip3Aa19 and Vip3Aa20 (Crickmore et al 2021), we refer to it as Vip3Aa.…”

Molecular Genetic Basis of Lab- and Field-Selected Bt Resistance in Pink Bollworm

“…Thus, it appears the Cry2Ab in bolls killed BX-R1 larvae, but the Cry1Ac did not [ 115 ]. By contrast, survival on Cry1Ac + Cry2Ab cotton relative to non-Bt cotton was 0.17 for the AZP-R2 strain, which had resistance ratios of 1100 for Cry1Ac and >710 for Cry2Ab [ 42 ], with resistance to Cry1Ac derived primarily from AZP-R and to Cry2Ab from Bt4-R2 [ 116 ]. These results suggest that the ability to survive exposure to Cry2Ab in Bt cotton for AZP-R2 but not BX-R1 primarily reflects the higher resistance to Cry2Ab in AZP-R2.…”

“…Bt cotton producing Cry1Ac alone and Cry1Ac + Cry2Ab have been used widely for decades to control pink bollworm and other lepidopteran pests. Although some Bt cotton also produces Cry1Fa and/or Vip3Aa targeting several lepidopteran pests, these proteins are not highly effective against pink bollworm [ 41 , 42 ].…”