Utilization of Δ 5,7 ‐ and Δ 8 ‐sterols by larvae of Heliothis zea

Larvae from two populations of Heliothis zea were reared on artificial diets containing various sterols, which supported suboptimal growth, and their tissue sterols were characterized in order to determine how these dietary sterols are utilized by this insect. The sterols studied included Δ 5,7 ‐sterols (7‐dehydrocholesterol or ergosterol), Δ 8 ‐sterols (lanosterol and/or 24‐dihydrolanosterol), and a Δ 5 ‐sterol (4,4‐dimethylcholesterol). Although larvae did not develop on 4,4‐dimethylcholesterol, those fed primarily Δ 8 ‐4,4,14‐trimethylsterols developed to the third instar. When the latter sterols were spared with cholesterol, the larvae reached the sixth instar and contained 4,4,14‐trimethylsterols as well as cholesterol in their tissues. When larvae were fed 7‐dehydrocholesterol, <1% of the larvae from one population developed to the sixth instar and these larvae contained 7‐dehydrocholesterol as their principal sterol. The other larvae successfully completed their larval stage when they were transferred from the diet containing 7‐dehydrocholesterol (or no sterol) to a diet containing cholesterol within at least 9 days. The sterol composition of larvae transferred from a diet containing cholesterol to a diet containing 7‐dehydrocholesterol, after they had reached 60% of their final weight, was 54% cholesterol and 46% 7‐dehydrocholesterol. The major sterol isolated from the tissues of the larvae fed ergosterol was also 7‐dehydrocholesterol. Therefore, although the larva of H. zea can dealkylate and saturate the side chain of the Δ 5,7,22 ‐24β‐methylsterol, it carries out little metabolism of the B ring of the nucleus. These studies demonstrate that, when Δ 5,7 ‐ or Δ 8 ‐sterols are the principal sterols in the diet of H. zea , they are absorbed and incorporated into its tissues, although they slow the rate of growth and may prevent complete development of the larva.