Plants as a Source of Materials With Insect Hormone Activity

Abstract

Certain plants contain substances with insect hormone like activity. These hormone analogues may influence insect-plant interactions like some other factors such as nutritional requirements, chemoreception, toxicity, etc.Experimental evidence indicates that an external supply of the hormonal substances, which comes from the plant without respect to the physiological control mechanisms, disturbs the precise synchronization of insect development and leads to the appearance of malformed creatures unable to survive and reproduce.We distinguish two types of hormonally active plant substances; a) Those with insect juvenile hormone activity, which are mainly aliphatic or monocyclic sesquiterpenes of farnesane or bisabolane types, and b) Substances with moulting hormone activity, which are polyhydroxy-steroid compounds related to ecdysone.The isoprenoid compounds with juvenile hormone activity occur in various plants.One of the most common ecdysone analogues of plant origin seems to be the 20-hydroxy ecdysone or ecdysterone. Hormonal activity of the plant substances is similar to, or higher than that of ecdysone. Whole series of ecdysone analogues have been isolated from various unrelated plants. In some cases they occur in extremely large quantities. There are some indications that they do act when fed in the diet.Plants which are known to contain analogues of insect hormones are more or less resistant, especially against susceptible insects. It does not seem impossible that certain plants have interacted in their evolution with insect feeders by using hormonomimetic materials --a method which we have not appreciated until now.Chemical interactions between plants and insects are also associated with secondary plant substances which are of little or no nutritional value. These substances influence various physiological processes resulting in growth inhibition, retardation of development or general toxicity. The presence of these physiologically active substances constitutes an important factor in the resistance of plants to insects (Beck, 1965). On the other hand, insects are able to identify and discriminate between the plants which are or are not suitable for their development and survival. They have developed specific chemosensory mechanisms of host-plant selection (Schoonhoven, 1968) as a result of evolutionary adaptations.Recent progress in insect endocrinology has revealed surprisingly that certain plants contain relatively large amounts of highly potent analogues of insect hormones, which are able to disturb the precise synchronization of insect development and so to suppress the insect's ability to survive and reproduce. The substances

Ecdysteroids act as inhibitors of calf skin collagenase and oxidative stress

“…Previous studies stated that they may be involved in plants defense mechanism against invading arthropods [2,5], in plant development (at low ecdysteroids content), and in the biochemical processes of storage, transportation, and metabolism of sterols (when at high ecdysteroids content). Many other pharmacological effects are attributed to these compounds [6]; however, reports on their collagenase inhibition potency are seldom in the literature.…”

Biological activity of two neem seed kernel extracts against the two‐spotted spider mite Tetranychus urticae Koch

“…S. Reda There would be some reasons explaining this phenomenon, it is direct influence of the substance o n the female ovaries or it is possible after contact application of any substance on the cuticle of the pest, the production of pheromones is disturbed. SLAMA (1969) gave many examples of disturbing insect development process by natural products.…”

Seed preferences of Pyrrhocoris apterus (Heteroptera: Pyrrhocoridae): Are there specialized trophic populations?

“…Pyrrhocorris apterus can certainly overcome strong phytochemical defences since it may complete its life cycle on seeds of trees that are generally avoided by phytophagous insects (Tilia, Robinia). For instance, the firebug is resistant to farnesol, contained in Tilia seeds, that exerts a juvenoid effect on other insects (Sláma, 1969); the firebug can apparently overcome the effects of allelopathic chemicals of Robinia as well. It is remarkable how quickly the firebug has exploited resources of this deuterochthonous tree present in Europe for just about 400 years, although it has never adapted to the native European species of Fabaceae (with the exception of the Sino-Siberian shrub Caragana arborescens widely planted in the Ukraine (Puchkov, 1956).…”