Metabolism of Insect Ecdysteroids and Significance of Insect Intestinal Microbiota

Abstract

Metabolism of ecdysteroids, insect moulting hormones, is described including that of active (20E)-20-hydroxyecdysone, showing a low activity, and inactive 20-phosphate. Transformation of active to inactive ecdysteroids (and vice versa) must be rapid and simple, with minimum energy requirements. In addition to ecdysteroid biosynthesis from phytosterols via cholesterol, insect larvae can obtain ecdysteroids from food as nonpolar and inactive esters with fatty acids. These esters penetrate through the midgut into the hemolymph in contrast to more polar ecdysteroids. The larvae excrete useless ecdysteroids during 24 hours. Wide diversity is shown of detoxified and deactivated pathways of ecdysteroids in insects, determined by bioassay. The biotests in insects mainly ecdysteroid tests are described in detail, in relation to digestion, the influence of intestinal symbiotic microbiota, detoxification of xenobiotics and subsequent inhibition of pathogenic microorganisms. Regulation and reduction of intestinal microorganisms are affected by an increased content of (20E)-20-hydroxyecdysone during ecdysis. Based on the current knowledge, the use of ecdysis by agonist formation for plant protection in agriculture would be suitable because the specificity of ecdysteroid receptors is low and they react as activators or inhibitors of insulin signalling cascades.