Insect steroid metabolism

Abstract

Insects are unable to biosynthesize the steroid nucleus and generally require an exogenous source of sterols. Two salient areas of insect steroid metabolism are the dealkylation and conversion of dietary C28 and C29 plant sterols to cholesterol and other C27 sterols, and the biosynthesis and metabolism of the steroidal insect molting hormones. Certain azasteroids and nonsteroidal amines block this conversion of 24-alkyl sterols to cholesterol and/or disrupt molting and development in insects. These inhibitors have served in charting metabolic pathways for steroids in insects and are serving as models in developing selective pesticidal chemicals and chemotherapeutic agents for use against insects and other invertebrate pests and parasites. The mode of action of some of these inhibitors on molting and development has been investigated in vivo and in vitro. Certain of these inhibitors represent a new class of insect hormonal compounds with a novel mode of action-the disruption of molting hormone metabolism. Research on sterol metabolism in insects provides important information on the comparative biochemistry and physiological functions of steroids in living systems.

25‐Azasteroid inhibition of development and conversion of C28 and C29 phytosterols to cholesterol in Spodoptera litura (F.)

“…as Manduca sexta, Tribolium confusum [5], HeZiothis zea [6], and Diatraea grandiosella [n, to name only a few representative species. It has also been shown that development in a number of species, including M .…”

Metabolism of Δ0‐, Δ5‐, and Δ7‐Sterols by Larvae of Heliothis zea

“…It is known that the structural requirements of other insects for sterols may vary depending upon the species [3,4]. For instance, cholesterol fulfills the cellular requirements for sterol in many insects, when it is obtained directly in the diet or derived from other sterols such as phytosterols; however, other species such as Drosophilu pachea [S], Epiluchnn vurivestis [6], and A f f a cephalofes isthrnicoZu [7] may use unusual sterols as their principal tissue sterols (ie, A7-, A'-, and A5!…”

Neutral Sterols of Cephalic Glands of Stingless Bees and Their Correlation with Sterols from Pollen

“…As phytosterols play an important role in sterol metabolism and ecdysteroid production [8,10,[23][24][25][26], the ingestion of exogenous sterols is essential for structural and metabolic components. Sterols seem to be absorbed mainly in the midgut, particularly in phytophagous species [27,28], moving quickly through mucosal cells [28].…”

“…Indeed, all phytophagous insects studied to date rely on exogenous sterol for growth, reproduction and development [6,7]. Many phytophagous insects are able to convert phytosterols in cholesterol through the dealkylation of compounds containing 28 to 29 carbon atoms, such as desmosterol, campesterol, brassicasterol, fucosterol, and sitosterol [8][9][10]. However, honeybees are unable to perform this conversion [11,12].…”