RESISTANCE TO BACILLUS-THURINGIENSIS SUBSP, KURSTAKI IN THE SUNFLOWER MOTH (LEPIDOPTERA, PYRALIDAE)

The sunflower moth, Homoeosoma electellum (Hulst), a major pest of commercial sunflower in North America, is susceptible to Bacillus thuringiensis Berliner. Besides being used as a biological insecticide, the B. thuringiensis endotoxin gene may be used to create transgenic sunflower (Helianthus annuus L.). Acute and chronic effects and resistance to the pathogen were evaluated in two populations of the sunflower moth. A susceptible sunflower moth population and a laboratory-selected, B. thuringiensis-resistant population did not differ in mortality, developmental periods, pupal weight, female/male ratios, or fecundity when B. thuringiensis was not present. However, when larvae were reared on diets treated with B. thuringiensis, the susceptible population had a significantly greater mortality, especially of females, than did the resistant population. Sublethal effects on the susceptible population included reduced pupal weights and lowered fecurdity in surviving females. In the resistant population, females were not more likely to die than males, and egg deposition was normal when larvae were treated with B. thuringiensis. Under present cultivation conditions, management of B. thuringiensis use in sunflower is not needed to prevent the development of a B. thuringiensis-resistant sunflower moth.