Role of phytoecdysteroids in insect pest management: A review

Abstract

Phytoecdysteroids are analogues of insect moulting steroid hormone, ecdysteroid. These are found in different plant groups and provide protection by deterring insects. Phytoecdysteroids have been synthesized in at least 27 families of Pteridophyta, 10 families of Gymnospermae and 74 families of Angiospermae. Chemically, phytoecdysteroids are triterpenoids, the group of compounds that includes triterpene saponins, phytosterols and phytoecdysteroids. These are polar steroids with sugar-like solubility properties. Over 300 phytoecdysteroids analogues have been identified so far and it has been speculated that there are over 1,000 possible structures in nature. These are synthesized from mevalonic acid and cholesterol. Phytoecdysteroids occur in relatively high concentration in many plants and comprise 0.001-3% of the dry weight. These have been isolated from all parts of plants in much higher amounts than those present in insects. Thus, plants are far better sources of ecdysteroids than insects. Different plant parts contain different amounts of ecdysteroids and that ecdysteroid concentration varies with season and geographical distribution of the plant. Ecdysteroids control insect development at all stages of the life cycle. Disruption of normal ecdysteroid level severely impairs insect development. Phytoecdysteroids mimic the insect ecdysteroid by binding to its receptors and eliciting a cascade of effects in insects. Phytoecdysteroids provide protection to plants by altering the normal levels of ecdysteroid hormone in adults and larvae in insects. Therefore, phytoecdysteroids can be an excellent replacement of synthetic insecticides in insect pest management programme.