Field deposition of Bt transgenic corn pollen: lethal effects on the monarch butterfly

We present the first evidence that transgenic Bacillus thuringiensis (Bt) c orn pollen naturally deposit ed on Asclepias syriaca; common milkweed, in a corn field causes significant mortality of Danaus plexippus L. (Lepidopter a: Danaidae) larvae. Larvae feeding for 48 h on A. syriaca plants naturally dusted with pollen from Bt corn plants suffered significantly higher rates of mortality at 48 h (20+/-3%) compacted to larvae feeding on leaves with no pollen (3+/-3%), or feeding on leaves with non-Bt pollen (0%). Mortality at 120 h of D. plexippus larvae exposed to 135 pollen grains/cm(2) of tran sgenic pollen for 48 h ranged from 37 to 70%. We found no sub-lethal effect s on D. plexippus adults reared from larvae that survived a 48-h exposure t o three concentrations of Bt pollen. Based on our quantification of the win d dispersal of this pollen beyond the edges of agricultural fields, we pred ict that the effects of transgenic pollen on D. plexippus may be observed a t least 10 m from transgenic field borders, However, the highest larval mor tality will likely occur on A. syriaca plants in corn fields or within 3 m of the edge of a transgenic corn field. We conclude that the ecological eff ects of transgenic insecticidal crops need to be evaluated more fully befor e they are planted over extensive areas.