Makisterone A: The molting hormone of larval Oncopeltus?

The major ecdysteroids of last‐stage Oncopeltus fasciatus larvae were determined by HPLC/RIA analysis. An ecdysteroid other than ecdysone or 20‐hydroxyecdysone, probably makisterone A, was the major ecdysteroid in hemolymph and in whole body extracts of 4‐ to 5‐day‐old larvae, when hemolymph ecdysteroid titers were at their peak. Little, if any, ecdysone or 20‐hydroxyecdysone was detected in the hemolymph. Bioassay of the relative activities of ecdysone, 20‐hydroxyecdysone, and makisterone A in last‐stage larvae revealed that makisterone A was ten times more active than 20‐hydroxyecdysone, and that ecdysone was inactive at doses as high as 1 mg/ml, its limit of solubility in 10% ethanol. Thus, it is suggested that makisterone A is the molting hormone in Oncopeltus. The implications of this discovery are discussed.