Absence of toxicity of Bacillus thuringiensis pollen to black swallowtailsunder field conditions

A single laboratory study on monarch butterflies has prompted widespread co ncern that corn pollen, engineered to express Bacillus thuringiensis (Bt) e ndotoxin, might travel beyond corn fields and cause mortality in nontarget lepidopterans. Among the lepidopterans at high potential risk from this tec hnology is the black swallowtail butterfly. Papilio polyxenes, whose host p lants in the midwestern U.S. are located principally in narrow strips betwe en roads and crop fields. A field study was performed to assess whether mor tality of early instar black swallowtails was associated either with proxim ity to a field of Bt corn or by levels of Bt pollen deposition on host plan ts. Potted host plants were infested with first instar black swallowtails a nd placed at intervals from the edge of a field of St corn (Pioneer 34R07 c ontaining Monsanto event 810) at the beginning of anthesis. We confirmed by ELISA that pollen from these plants contained Cry1Ab endotoxin (2.125 +/- 0.289 ng/g). Although many of the larvae died during the 7 days that the ex periments were run, there was no relationship between mortality and proximi ty to the field or pollen deposition on host plants. Moreover, pollen from these same plants failed to cause mortality in the laboratory at the highes t pollen dose tested (10,000 grains/cm(2)), a level that far exceeded the h ighest pollen density observed in the field (200 grains/cm(2)). We conclude that Bt pollen of the variety tested is unlikely to affect wild population s of black swallowtails. Thus, our results suggest that at least some poten tial nontarget effects of the use of transgenic plants may be manageable.