Submitted to: International Conference on Bacillus thuringiensis
Publication Type: Abstract Only
Publication Acceptance Date: October 15, 2000
Publication Date: N/A
Technical Abstract: Research was conducted summer 1999 to determine if Bacillus thuringiensis (Bt) corn pollen presents a toxic risk to monarch butterflies, Danaus plexippus. Preliminary data strongly indicate that pollen from Bt corn events MON810 and CBH351 do not influence monarch larval mortality or development at levels normally found near cornfields during pollen shed, although more analysis remains to be done and peer-reviewed. With Bt corn event 176, the results were problematic when the pollen was considered only from a toxic view rather than a toxic plus exposure possibility. Our pollen deposition results suggest that there are many mitigating factors: pollen is heavy and most is deposited within a 2-3 m of cornfield, only a fraction of pollen (our study ~ 30% on average) stays on milkweed leaves, and rain washes most of pollen (our study ~ 90%) off of milkweed leaves. Choice and feeding results suggest that monarch larvae are influenced by the presence of pollen. When presented with leaves with no pollen and very high amounts (~ 600 grains/cm2) of pollen, more larvae were found on the leaves with no pollen. Weight and survival data indicate that larvae feeding on milkweed leaves with high (~150 grains/cm2) and moderate (~ 60 grains/cm2) amounts of pollen from the MON810 and CBH351 are not affected. At the very high levels of pollen (~ 600 grains/cm2) these same larvae were smaller than larvae from the control treatments, but survival was not different from that of the controls. Larvae feeding on leaves with pollen from the 176 type of corn were affected at each of the pollen density levels. Bt 176 corn represents about 2.5% of total corn planted in the United States. A Monarch Workshop was convened February for planning research activities for the 2000 growing season. A summary these activities also will be presented.