Understanding insect parasitoids life history behaviour for optimal utilization in biological control of tropical injurious pest - a review

Parasitoids are a key component of most terrestrial ecosystems due to their numbers and ecological significance due to he nature of their life cycle which partly depend on other insects for their survival. They are vitally important for the maintenance of biodiversity being involved in a vast number of trophic interactions including regulatory effect on insect pest populations. There are four insect orders that are particularly prominent for this type of life history. These are Hymenoptera, Diptera, Coleoptera and Neuroptera. The greatest number is found in the order Hymenoptera, which account for nearly 75% of the estimated number of parasitoid species. There are considerable variations in parasitism of insect parasitoids. These may be I diobionts, whose hosts stop development, when they are parasitized and Koinobionts which allow the hosts to continue their development until the parasitoid’s offspring matures. Reports have shown that species richness of koinobionts parasitoids tends to decrease toward the tropics while idiobionts richness does it less severely. Such pattern was howeve intrinsically related to the host feeding niche. In hymenopteran parasitoid complexes however the richness of both idiobionts and koinobionts falls toward the tropics in exophytic hosts, while on endophytic hosts, there are no changes in species richness for both types of parasitoids. Biological control is the central stone of integrated pest management (IPM) paradigm and natural enemies are becoming an increasingly desirable prospect in lieu of chemical insecticides. Although hymenopteran parasitoids are widely used in the control of insect pest due to their Diversity and species richness, Coleopterans parasitoids could be useful in suppressing pest due to the pattern of their parasitism. Host selection strategies of insect parasitoids are largely influenced by chemical signals from plants attacked by insect pest. Their competitive fitness and reproductive success will therefore depend extensively on the ability to employ such signals more efficiently.Keywords: Behaviour, Biological control, Diversity, Insect parasitoids, Plant metabolite