Abstract
It is well documented that cytochrome P450 enzymes play a central role in metabolic resistance to natural plant toxins and synthetic pesticides. Using insecticide-susceptible and -resistant strains ofDrosophila melanogasterand monophagous Sonoran Desert drosophilids, the current study looked for a correlation between resistance to toxic cactus alkaloids and resistance to pesticides (DDT and propoxur) or a toxic, noncactus alkaloid (nicotine). Resistance to cactus alkaloids in cactophilicDrosophilawas not associated with resistance to DDT or propoxur. Conversely, a DDT-resistant strain ofD. melanogaster(Hikone R) was no more tolerant of cactus alkaloids than a susceptible strain (Canton S). Cactus alkaloid-metabolizingDrosophilawere, however, less susceptible to nicotine than a noncactophilic species (D. melanogasterstrain Canton S). These data suggest that resistance to cactus alkaloids in monophagous desertDrosophilainvolves the activity of cytochrome P450 isoforms with substrate specificities sufficiently narrow to preclude detectablein vivoactivity on compounds other than those that are chemically similar. These results are in contrast to what has generally been reported for more highly polyphagous insect species.
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