Larval dispersal and survival of Scirpophaga incertulas (Lepidoptera : Pyralidae) and Chilo suppressalis (Lepidoptera : Crambidae) on cry1Ab-transformed and non-transgenic rice

Sowing seed mixtures of transgenic and nontransgenic plants is one approach to establishing refuges for resistance management of crops transformed wit h Bacillus thuringiensis (Bt) toxins. We studied larval dispersal and survi val of two rice stern borers, Scirpophaga incertulas (Walker) and Chilo sup pressalis (Walker), to evaluate the potential effectiveness of seed mixture s for resistance management of Bt rice, Oryza sativa L. Experiments were co nducted with two cry1Ab-transformed rice varieties, 'IR58' and 'Tarom Molai i', and corresponding nontransgenic controls. During 0-24 and 24-48 h after egg hatch, the proportion of C. suppressalis larvae dispersing from the na tal plant did not differ between transgenic and control plants for either r ice variety Dispersal by S. incertulas did not differ between transgenic an d control plants of IR58 during either 0-24 or 24-48 h, but a greater propo rtion of S. incertulas larvae dispersed from transgenic Tarom Molaii than f rom control plants 24-48 h after eclosion. Larvae that dispersed 0-24 h aft er eclosion on IR58 and 0-24 and 24-48 h after eclosion on Tarom Molaii wer e collected and transferred to stern pieces of control plants. No differenc es in survival were detected between larvae that dispersed from transgenic or control plants 24 (IR58) or 72 h (Tarom Molaii) after dispersal. Because both stem borer species move among plants during larval development, seed mixtures may not be the most effective approach to maintaining refuges for resistance management. However, additional experiments to compare the dispe rsal and fitness of Bt-resistant and -susceptible stem borer larvae are nee ded.