Integerrimine (ITR), a pyrrolizidine alkaloid from Seequally potent in inducing spots in a dose-related necio brasiliensis, was tested for genotoxicity using manner in the marker heterozygotes of both crosses. the wing somatic mutation and recombination test This indicates that the bioactivation capacity pres-(SMART) in Drosophila melanogaster. The com-ent in larvae of the ST cross is sufficient to reveal pound was administered by chronic feeding (48 the genotoxic activity of ITR. In the balancer heterohours) of 3-day-old larvae. Two different crosses in-zygotes of both crosses, where all recombinational volving the markers flare (flr) and multiple wing events are eliminated due to the inversions, the frehairs (mwh) were used, that is, the standard (ST) quencies of induced spots were considerably recross and the high bioactivation (HB) cross, which duced which documents the recombinagenic activhas a high cytochrome P450-dependent bioactiva-ity of ITR. Linear regression analysis of the dose tion capacity. In both crosses, the wings of two types response relationships for both genotypes shows of progeny were analyzed, that is, inversion-free that 85% to 90% of the wing spots are due to mitotic marker heterozygotes and balancer heterozygotes recombination. Environ. Mol. Mutagen 29:91-97, carrying multiple inversions. ITR was found to be 1997 ᭧ 1997 Wiley-Liss, Inc.