Effects of corn plants and corn pollen on monarch butterfly (Lepidoptera :Danaidae) oviposition behavior

The oviposition behavior of adult insects can have a major impact on the le vel of exposure of their offspring to natural and artificial toxins. Pollen from Pt-corn hybrids represents a novel toxin and very little is known reg arding its detection and possible avoidance by ovipositing females. The eff ect of corn plant proximity and corn pollen presence on the oviposition beh avior of the monarch butterfly, Danaus plexippus (L.), was assessed in cage and flight chamber studies. The proportions of monarch eggs oviposited on milkweed plants dusted pollen from with a Bt-corn hybrid, an untransformed hybrid, gravel dust, and undusted control plants were recorded from a cage study. None of the treatments differed significantly in the relative propor tion of eggs found. The effect of Bt and untransformed corn plant proximity and corn pollen presence was also assessed in a flight chamber. A signific antly higher proportion of eggs (96%) were recovered from patches of milkwe ed plants not surrounded by corn plants, and a significantly higher proport ion of eggs (nearly 70%) were recovered from patches of milkweed plants not dusted with corn pollen. There were no significant differences in the effe cts of Bt corn plants or corn pollen compared with untransformed plants or pollen. These results may have important implications for the level of expo sure of monarch larvae to Pt-corn pollen.