Impact of pollen-induced Bt toxicity by a multi-toxin corn variety on survivorship and growth of corn earworm and its implications on current IRM practices

Effects of cross pollination and resulting pollen-induced Bt toxicity in corn kernel on survivorship and growth of corn earworm, Helicoverpa zea (Boddie) were studied. A multi-toxin transgenic Bt variety and it’s near non-Bt isoline were used as parent lines. Four different crosses viz. Bt X Bt, Bt X non-Bt, Non-Bt X Bt and non-Bt X non-Bt were made during the summers of 2011 and 2012. Each hand pollinated ear was infested with 25 corn earworm neonates. Growth and survival of corn earworm were recorded 10 days after infestation. A significantly lower number of corn earworm survivors were observed in Bt maternal plants, regardless of pollen parent. For crosses where the maternal plant as non-Bt, the pollen parent had a significant impact on corn earworm growth and survivorship. Intermediate survivorship of corn earworm on non-Bt maternal plants pollinated by Bt pollen indicated sub lethal exposure to Bt toxins in non-Bt ears due to Bt pollen induced toxicity. Results indicated that  pollen mediated gene flow from nearby Bt plants could affect the growth and survival of corn earworm on non-Bt refuge plants, reducing  its quality as a refuge since insects are selected for Bt toxin in their cross pollinated kernels.