Lack of tolerance development following sublethal Cry1 proteins exposure in Spodoptera exigua

BACKGROUNDThe insecticidal proteins derived from Bacillus thuringiensis Berliner (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 may contribute tolerance, but the specific effects of sequential exposure to purified Cry1 proteins remain unclear. This study aimed to assess whether prior exposure of Spodoptera exigua (Huber, 1808) neonate larvae to sublethal concentrations of Cry1Ab and Cry1Ca proteins would heighten their tolerance upon subsequent exposure, and whether such effects would extend to their offspring. RESULTSPre-exposure to Cry1Ab 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 in practical terms. Similarly, transgenerational analysis revealed no enhancement of tolerance; rather, there was a negative impact on the offsprings response in some cases. CONCLUSIONThese findings indicate that although previous studies have documented that sublethal contact with bacterial preparations may significantly affect the insect tolerance, exposure to purified Cry proteins is unlikely to lead to the development of tolerance in S. exigua. Therefore, our findings suggest that sublethal exposure to these Cry1 proteins may not significantly affect the long-term efficacy of Bt-based pest management strategies relaying on them.