Simplified preparations, such as isolated abdomens, were used to study the effect of farnesyl methyl ether (a juvenile hormone mimic) and ecdysone on ovarian development and adult development in Malacosoma pluviale. Untreated isolated abdomens showed very limited ovarian development and failed to form imaginal cuticle, thus indicating a lack of adult development. Topical application of farnesyl methyl ether to the isolated abdomens blocked the ovarian development completely and no adult development ensued either. Both adult development and ovarian development of the isolated abdomens were stimulated by ecdysone injections. Thus, adult development and ovarian development in M. pluviale seem to be closely related.