The effects of the structure of sterols on the development of Heliothis zea

Heliothis zea was reared on artificial diets which lacked supplementation with plant materials but were supplemented with different sterols in order to determine how certain structural features of a sterol molecule affect the development of this insect. We found that sitosterol and cholesterol supported a more rapid rate of growth than did campesterol. Larvae did not moult when they ingested 5-pregnen-3β-ol. Larvae utilized spinasterol more efficiently than lathosterol. Such a pronounced effect was not observed in the Δ⁵-series. The substitution of a Δ⁷-bond (spinasterol, dihydrospinasterol, lathosterol) for the Δ⁵-bond (stigmasterol, sitosterol, cholesterol) in the 24-ethyl- and desalkylsterols reduced the rate of growth of the larvae. Although larvae developed normally on cholesterol, the addition of a Δ⁷-bond to give the Δ^5,7-diene system apparently altered the functionality of the molecule because 7-dehydrocholesterol did not support larval development. The growth of larvae was also inhibited, although not prevented, when they consumed diets which contained ergosterol. In contrast, the larvae completed their development more rapidly on brassicasterol which lacked the Δ⁷-bond. Cholestanol supported the complete development of the insect. H. zea is unusual among investigated insects because it develops both on cholestanol and lathosterol but does not utilize ergosterol efficiently and fails to grow on 7-dehydrocholesterol.