STAGE-SPECIFIC MORTALITY OF COLORADO POTATO BEETLE (COLEOPTERA, CHRYSOMELIDAE) FEEDING ON TRANSGENIC POTATOES

We have further examined the characteristics of resistance to Bacillus thuringiensis Berliner in a strain of Colorado potato beetles, Leptin otarsa decemlineata (Say). We compared the toxicity of CryIIIA toxin o f transgenic potato plants containing the CryIIIA gene to each larval stage of susceptible and resistant strains of Colorado potato beetle. In bioassays, resistance ratios for resistant 2nd instars were substan tially higher than ratios for the other instars. Second instars from s trains of Colorado potato beetles resistant to chemical insecticides w ere susceptible to transgenic potatoes. For all strains, Ist instars w ere sensitive to B. thuringiensis toxins, whereas 3rd instars were typ ically insensitive. Second and older instars of the B. thuringiensis-r esistant strain had much higher survival compared with the susceptible strain after 96 h exposure to transgenic potatoes. Second and older r esistant instars gained weight on transgenic plants, but at a signific antly slower rate than on conventional foliage. Larvae of the suscepti ble strain typically lost weight when they fed on transgenic foliage. Adult beetles From the resistant strain experienced approximate to 25% mortality in 14 d while feeding on transgenic potatoes, whereas the s usceptible adults died.