Response ofDrosophila tocis‐ andtrans‐22‐dehydrocholesterol: I. A survey

Cis‐ andtrans‐22‐dehydrocholesterol were added to media for 10 species ofDrosophila. Thecis isomer prevented normal maturation of 4 species and thetrans isomer was toxic to 9. These findings were corroborated by tests with 4 representative species on a sterol‐deficient medium under axenic conditions. Addition of cholesterol to the latter overcame the toxicity of thetrans isomer.Trans‐22‐dehydrocholesterol may be acting as a competitive inhibitor in the metabolism of phytosterols to cholesterol or ecdysone by the insects.