Non-target effects of Bt corn pollen on the Monarch butterfly (Lepidoptera: Danaidae)

North Central Branch of the Entomological Society of America

1999 Annual Meeting 28mar99

L. Hansen, Iowa State University, Ames , IA 50011

J. Obrycki, Iowa State University, Ames, IA 50011

Contact e-mail: lrahnsen@iastate.edu

The expression and dispersal of Bt toxin in the pollen from transgenic crop plants may pose a risk to non-target Lepidopterans. When Bt corn pollen lands on the leaves of plants in and around corn fields, it exposes non-target Lepidopteran larvae feeding on these plants to Bt toxins. In Iowa, where the landscape is dominated by row-crop agriculture, areas effected could include a significant portion of non-cultivated areas, including remnant prairies, roadside ditches and wetlands. The monarch, Danaus plexippus (Lepidoptera: Danaidae) was chosen as the non-target Lepidopteran species for this study because it is a common butterfly species that feeds on several species of milkweed, Asclepias. Asclepias syriaca (Asclepiadaceae) commonly grows in road ditches, grassy areas between fields, and within corn fields, so it is likely to have Bt corn pollen deposited upon it. The first step of this study was to determine the amount of corn pollen deposited on A. syriaca leaves within and adjacent to a Bt corn field at 0 m, 1m, and 3m. The highest levels of pollen deposition was found on plants within the corn field, and lowest levels found at three meters from the edge of the corn field. Leaf samples taken from within and at the edge of the corn field were used to assess mortality of first instar monarch, D. plexippus exposed Bt and non-Bt corn pollen. Within 48 hours, there was 19% mortality in the Bt corn pollen treatment compared to 0% on non-Bt corn pollen exposed plants and 3% in the no pollen controls.