No abstract

No abstract

Heliothis zea was reared on artificial diets containing A5-sterols (cholesterol, campesterol, or sitosterol), A'-sterols (lathosterol, epifungisterol, or spinasterol), or A'-sterols (cholestanol, epicoprostanol, carnpestanol, or sitostanol) in order to determine how different dietary sterols affect the type of sterols present in the tissues of the late-sixth-instar larva. Although all of the dietary sterols (except epicoprostanol) supported the growth of the larvae, not all of the sterols were metabolized to the same end products. In each case, at least 80% of the sterols in the tissues of the larvae retained the same nucleus as that of the dietary sterol, indicating that H. zea carries out very little metabolism of ring B of A5-, A7-, and A'-sterols. The larvae dealkylated the A' -, A'-, and A'-alkylsterols to 24desalkylsterols, but a greater percentage of the A5-alkylsterols were metabolized in this manner. The sterols present as free sterols in the larva were also present as esterifed sterols which accounted for 2-4% of the total sterols. Therefore, the sterol composition of the tissues of H. zea can be altered by varying the dietary sterols.

No abstract

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 A5r7-sterols (7-dehydrocholesterol or ergosterol), A8-sterols (lanosterol andlor 2Cdihydro-lanosterol), and a A5-sterol (4,4-dimethylcholesterol). Although larvae did not develop on 4,4dimethylcholesterol, those fed primarily A8-4,4,14trimethyl-sterols 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 A5,7,22-24fhnethylsteroI, it carries out little metabolism of the B ring of the nucleus. These studies demonstrate that, when A5r7-or A8-sterols are the principal sterols in the diet of H. zea, they are absorbed and incorporated into i t s tissues, although they slow the rate of growth and may prevent complete development of the larva.