Positive association between resistance to Bacillus thuringiensis and overwintering survival of cabbage loopers, Trichoplusia ni (Lepidoptera: Noctuidae)

• Published in: Bulletin of entomological research 2008-06, Vol.98 (3), p.317-322
• Main Authors: Caron, V., Myers, J.H.
• Format: Article
• Language: English
• Subjects: Adaptation, Biological - genetics; Animals; Bacillus thuringiensis; Bacillus thuringiensis subsp. kurstaki; Bacterial Proteins; Biological and medical sciences; Biological control; Brassica; Bt resistance; Butterflies & moths; cold stress; Cold Temperature; cold tolerance; Control; Endotoxins; evolution of resistance; Fecundity; fitness costs; Fundamental and applied biological sciences. Psychology; Genetically altered foods; greenhouse populations; Greenhouses; Hemolysin Proteins; insect fitness; insecticide resistance; Insecticide Resistance - genetics; Insecticides; Lepidoptera; mortality; Moths - physiology; Noctuidae; Overwintering; pest management; Pesticides; Phytopathology. Animal pests. Plant and forest protection; Protozoa. Invertebrates; pupae; Survival; Trichoplusia ni; Winter
• ISSN: 0007-4853; 1475-2670
• DOI: 10.1017/S0007485307005597

Development of resistance to insecticides has generally been associated with fitness costs that may be magnified under challenging conditions. Lepidopterans which are resistant to the biopesticide Bacillus thuringiensis subsp. kurstaki (Btk) have been shown to have reduced fitness, such as lower survival when subjected to overwintering stress. Recently, resistance to Btk has been found in some populations of Trichoplusia ni Hübner in greenhouses in British Columbia. This situation provides an opportunity to investigate potential trade-offs between overwintering survival and insecticide resistance in a major pest species. Here, we assess the survival and eventual fecundity of Btk resistant and susceptible T. ni pupae exposed to cool temperatures. Contrary to our expectations, resistant T. ni had higher overwintering survival than susceptible individuals. This is the first account of a potential advantage associated with Btk resistance. Resistant and susceptible moths had reduced fecundity and smaller progeny after cold exposure compared to controls, and this may counteract the survival advantage. Nevertheless, it seems unlikely that this is sufficient to select out the resistant phenotype in the presence of strong selection for resistance and in the absence of immigration of susceptible moths. The appearance of resistance without evidence of a trade-off in overwintering survival presents a major challenge to management in production greenhouses.