Lack of Tolerance Development Following Oral Exposure Tosublethal Cry1 and Vip3Aa Proteins in Spodoptera exigua...

Insecticidal proteins derived from Bacillus thuringiensis (Bt) have been effectively employed in controlling lepidopteran pests, notably in transgenic crops targeting Spodoptera species. However, concerns have arisen regarding the long-term efficacy due to the emergence of tolerant and resistant insect populations. Prior research suggested that repeated exposures to Bt, which contains a mixture of spores and crystals, may contribute to the development of tolerance; however, the specific effects of sequential exposure to purified Cry1 and Vip3Aa proteins remain unclear. This study aimed to assess whether prior exposure of Spodoptera exigua neonate larvae to sublethal concentrations of Cry1Ab, Cry1Ca or Vip3Aa proteins would heighten their tolerance upon subsequent exposure, and whether such effects would extend to their offspring. Pre-exposure to Cry1Ab or Vip3Aa did not affect larval responses to the toxin. For Cry1Ca, a slight increase was observed under one treatment condition, but the effect was not considered biologically relevant. Transgenerational analysis revealed no enhancement of tolerance; rather, there was a negative impact on the offspring's response in some cases. These findings indicate that although previous studies have documented that sublethal contact with bacterial preparations may significantly affect insect tolerance, exposure to sublethal doses of purified Cry1 and Vip3Aa proteins is unlikely to lead to the development of tolerance in S. exigua.