ABSTRACT
In a few known exceptions, microbial symbionts provide sufficient essential sterol for the insect. As in many organisms, sterols serve a dual role both as components of cell membranes and as precursors to steroid hormones which, in insects, are the molting hormones. Although sterol metabolism has been investigated in a small number of insect species, as an increasing number of species is examined, it becomes increasingly clear that it is very difficult to generalize sterol metabolism in insects. Discussion in this chapter concentrates on neutral sterol metabolism and touch only briefly on ecdysteroid biosynthesis. Members of the order Diptera, which includes flies and mosquitoes, have also been found to display considerable variability in the utilization of dietary sterols. The amount of variability in sterol metabolism discovered so far is quite striking when one considers the relatively small percentage of the nearly one million identified insect species that have been investigated with respect to sterol metabolism.
