Monooxygenase activities of fat body and gut homogenates of monarch butterfly larvae,Danaus plexippus, fed four cardenolide-containing milkweeds,Asclepias spp.

Monarch butterfly larvae were examined for NADPH-dependent monooxygenase activities. Midgut and fat body homogenates catalyzed aldrin epoxidation andp-chloro-N-methylanilineN-demethylation at consistently low rates compared to many other lepidopteran larvae. Homogenates from larvae collected from four different milkweeds (Asclepias spp.) with quite different cardenolide contents had similar levels of activity. There were no detectable variations in activity due to season or year of collection.