Occurrence of Danaus plexippus L. (Lepidoptera: Danaidae) on milkweeds (Asclepias syriaca) in transgenic Bt corn agroecosystems

The potential negative effects of transgenic Bt corn on the monarch butterfly, Danaus plexippus, requires quantification of the presence of D. plexippus in the field and of the effect of Bt corn tissues on oviposition and larval survival. During a 2-year field study, D. plexippus females laid similar number of eggs on Asclepias syriaca in corn fields and on A. syriaca growing in roadside habitats parallel to corn fields. In 1999 and 2000 similar number of D. plexippus larvae were observed on A. syriaca in corn fields and roadside habitats, whereas a greater proportion of A. syriaca in corn fields were infested by at least one D. plexippus larva in 2000. Similar number of eggs were laid in transgenic Bt and non-Bt corn fields, indicating that females did not avoid leaves dusted with anthers and 672 Bt pollen grains/cm^2. Similar number of D. plexippus larvae were found in and near Bt corn fields compared to non-Bt corn fields following corn anthesis. In 2000, transgenic Event MON810 Bt corn pollen and anthers had no measurable effects on D. plexippus oviposition or larval survival.