Submitted to: Proceedings of the National Academy of Sciences
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/22/2001
Publication Date: N/A
Citation: Interpretive Summary: A consortium of scientists has studied whether pollen from transgenic Bacillus thuringiensis (Bt) corn could be hazardous to the caterpillars of the monarch butterfly. These studies assess ecological risk by considering toxicological effect and environmental exposure. For this study field experiments were conducted to assess the survival and fitness of monarch larvae following exposure to pollen from three types of Bt corn or to an insecticide commonly used against insect pests of corn. Five independent studies found that pollen from event Bt11 hybrids had no measurable effect on caterpillars in cornfields. Similar results were found with Mon810 hybrids. Caterpillars exposed to pollen from event 176 hybrids had lower weights and reduced survival. Most larvae died within hours after feeding on milkweed leaves exposed to a sprayed insecticide. This information will be useful for all stakeholders interested in the potential nontarget effects of transgenic plants.
Technical Abstract: Survival and fitness of monarch larvae following exposure to pollen from three Bacillus thuringiensis (Bt) Cry1Ab-expressing corn events or to the insecticide, lambda-cyhalothrin, were examined in field studies. Five independent studies found that pollen from event Bt11 hybrids had no measurable effect on monarch larvae in cornfields. Specifically, Bt11 pollen had no effect through to adulthood on growth or survival of first o third instars exposed for 5 days to ~55 and 97 pollen grains/cm2 respectively. Similarly, no differences in larval survivorship were observed following a 4-day exposure period to leaves with 504-586 (within fields) or 18-22 (outside the field) pollen grains/cm2 collected from Bt11 and non-Bt sweet corn fields. However, survivorship and weight gain were drastically reduced in non-Bt fields treated with lambda-cyhalothrin. The effects of Bt11 and Mon810 pollen on the survivorship of larvae feeding 14 to 22 days on milkweeds in fields were negligible. In contrast, larvae exposed to 67 pollen grains/cm2 on milkweed leaves from within an event 176 field exhibited 60% lower survivorship and 42% less weight gain compared with those exposed to leaves from outside the field. These studies indicate that the impact of Bt corn on monarch larvae largely depends on the specific Bt event. Pollen from event Bt11 and Mon810 hybrids had no measurable effect on monarch larvae, but larvae exposed to pollen from event 176 hybrids had lower weights and reduced survival. Most larvae died within hours after feeding on milkweed leaves exposed to a sprayed insecticide.