Laboratory studies on the effects of pollen from Bt-maize on larvae of some butterfly species

Three lepidopteran species were tested to determine their susceptibility against the ingestion of pollen from genetically modified maize plants. To prove the existence of dose-response relations between the applied amount of pollen (Bt-maize) and the damages on the tested larvae, a method was developed which makes it possible to feed caterpillars with defined amounts of pollen. If their food plants were contaminated with pollen of a cultivar of the Bt-176 maize-line Pieris brassicae , Pieris rapae and Plutella xylostella -larvae fed less, grew more slowly and showed a higher mortality than caterpillars of an untreated control group. The 50% lethality (LD50 )-values were calculated for P.xylostella (L-4 ) with 19.2, for P. rapae (L-2 ) with 39.0 and also for P. brassicae (L-2 ) with 139.2 pollen of the transgenic maize Pactol CB. Studies with P. brassicae -caterpillars of different larval stages indicated, that older individuals showed a higher tolerance against pollen from Bt-maize than younger ones. It must be stated on the basis of the present studies, that ingestion of non-transgenic maize pollen has neither a positive nor a negative effect on caterpillars. It becomes clear from the information presented here that it is still difficult to make general statements about the endangering of butterflies, arising from cultivation of genetically modified maize lines. Further investigations on this issue are needed. Initially, the LD50 -values concerning the larvae of certain butterfly species have to be determined to anticipate the risks, and in addition the distances between habitats with caterpillar host plants and maize fields, and the abundance of these plants have to be considered.