Taxonomy and Bionomics of the Insect Parasites of Rice Leafhoppers and Planthoppers in the Philippines and their Importance in Natural Biological Control

Outbreaks of rice hoppers have often threatened rice production in Asia and by transmitting virus diseases, they have constantly alarmed the rice growers even at low densities. The natural enemy complex of these pests in the Philippines is not well understood but in view of the high biotic potential of the pests, it is reasonable to assume that at most times their population growth is curtailed by natural enemies. Field and laboratory investigations were undertaken to find out various species of these beneficial insects and their role in checking pest population, the results of which on insect parasites are presented in this paper. Two groups of parasi:t9s were found associated with rice hoppers, viz. egg parasites,. which include the hymenopterans, Mymaridae and Trichogrammatidae and the nymphal-adult parasites, including Dryinidae (Hymenopteral, Pipunculidae (Diptera) and Strepsiptera. Parasitization by these was studied in dryland and wetland environments at IRRI farm. Problems of estimating field parasitism were studied and some improved techniques a­dopted. Parasitization of eggs remained more stable as compared to that of nymphs and adults, which increased in the latter half of the crop period. Pipunculids favored dryland environment while the Strepsipterans wetland. Biology, behavior, parasitization abilities and effects of parasitization on the hosts were studied in the laboratory. Egg parasitoids were found to have a capacity to deposit most of their eggs on the first day of life, thus succeeding in leaving more progeny than the nymphal-adult parasites in, case of early mortality. Biological control potential is discussed and taxonomic characters supported by figures are given to facilitate identification of species.