Characterization of Cry2Ab2 resistance in Crocidosema sp. (Lepidoptera: Tortricidae): resistance selection, inheritance, cross‐resistance patterns, and fitness costs
Abstract BACKGROUND The soybean bud borer, Crocidosema sp., evolved field resistance to Cry1Ac soybean in Brazil, raising concerns regarding the durability of Bacillus thuringiensis (Bt) soybean technologies and potential evolution of resistance to additional Bt proteins. Here, a Cry2Ab2‐resistant strain of Crocidosema sp. was selected and characterized to investigate resistance inheritance, cross‐resistance to Cry1 proteins, and fitness costs. RESULTS Laboratory selection with leaves of Cry2Ab2 soybean generated a resistant strain of Crocidosema sp. exhibiting > 15 000‐fold resistance relative to a susceptible strain. Reciprocal crosses showed resistance ratios of 8.46‐ and 30.17‐fold, suggesting autosomal inheritance, although a maternal effect could not be completely excluded. Effective dominance ( D ML ) indicated incompletely recessive resistance under exposure to Cry2Ab2 in diet‐overlay bioassays ( D ML = 0.08–0.25) and on Cry2Ab2 soybean ( D ML = 0.16–0.26). Backcross analyses indicated a major‐gene contribution, with potential involvement of additional genetic factors. Bioassays with Cry1Ac and Cry1A.105 proteins and Bt soybean revealed no cross‐resistance between Cry2Ab2 and these Cry1 proteins. Fitness assessments indicated no apparent cost of resistance, with a higher intrinsic rate of population increase ( r ₘ) in the resistant than susceptible strain (0.112 versus 0.098) and a relative fitness of 1.14. CONCLUSIONS Resistance to Cry2Ab2 in Crocidosema sp. appears to be autosomal and incompletely recessive, with a major‐gene contribution to the resistance phenotype. Cry2Ab2 resistance did not confer cross‐resistance to Cry1Ac or Cry1A.105, supporting Cry2Ab2 as an additional mode of action in Bt soybean technologies. The lack of an apparent fitness cost may favor the persistence of resistance alleles in the field, reinforcing the need for effective resistance management. © 2026 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.