Stage-specific mortality of Colorado potato beetle (Coleoptera: Chrysomelidae) feeding on transgenic potatoes

Abstract

We have further examined the characteristics of resistance to Bacillus thuringiensis Berliner in a strain of Colorado potato beetles, Leptinotarsa decemlincata (Say). We compared the toxicity of CryIIIA toxin of transgenic potato plants containing the CryIIIA gene to each larval stage of susceptible and resistant strains of Colorado potato beetle. In biosssays, resistance ratios for resistant 2nd instars were substantially higher than ratios for the other instars. Second instars from strains of Colorado potato beetles resistant to chemical insecticides were susceptible to transgenic potatoes. For all strains, 1st instars were sensitive to B thuringiensis toxins, whereas 3rd instars were typically insensitive. Second and older instars of the B thuringiensis-resistant strain had much higher survival compared with the susceptible strain after 96 h exposure to transgenic potatoes. Second and older resistant instars gained weight on transgenic plants, but at a significantly slower rate than on conventional foliage. Larvae of the susceptible strain typically lost weight when they fed on transgenic foliage. Adult beetles from the resistant strain experienced ≃25% mortality in 14 d while feeding on transgenic potatoes, whereas the susceptible adults died.