Ecdysteroids as defensive chemicals

Abstract

Ecdysteroids are best known as the steroid hormones of insects and other arthropods, where they are involved in the regulation of moulting, development and reproduction, but, in certain specific cases, they are present in much higher amounts as components of defensive secretions which serve to deter predators. Further, a wide range of ecdysteroid analogues are present in a significant proportion of plant and algal species (phytoecdysteroids) and some fungal species (mycoecdysteroids). The purpose of phytoecdysteroids seems to be to reduce invertebrate predation, either as antifeedants acting on taste receptors, or as endocrine disruptors acting through intracellular ecdysteroid receptors. While many invertebrate species are very sensitive to ingested ecdysteroids, others have developed very efficient avoidance or detoxification strategies, which allow them to evade the detrimental consequences of ecdysteroids in the diet. The purpose of this review is to assess the evidence for the roles of ecdysteroids as defence compounds, identify gaps in our knowledge and indicate prospects for future research.