Establishment of fundamental theory for classical biological control - a case study on biological control of arrowhead scale -

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Biological control of Unaspis yanonensis by using two introduced parasitoids, Aphytis yanonensis and Coccobius fulvus was examined as a case study for establishing basic theory of classical biological control. First, I investigated biological characteristics of the two parasitoids to evaluate their effectiveness as natural enemies. As the result, the two parasitoids were complementary as natural enemies of U. yanonensis, and it was indicated that combination of the two parasitoids resulted better results as biological control of the pest. Second, results of the study of population dynamics of U. yanonensis in orchards after the introduction of one of the parasitoids indicated that single species introduction of either species was resulted in the reduction of the population level of U. yanonensis. Howevere, density of U. yanonensis reduced again after the introduction of C. fulvus to the orchard where only A. yanonensis had been introduced This suggested the superiority of the multiple species introduction in classical biological control. The analysis of population dynamics of U. yanonensis in the orchard where the parasitoids were also introduced indicted the superiority of the multiple species introduction. On the other hand, analysis of the existing information on parasitism of the two parasitoids on indegenous scale insects suggested that there was not so serious environmental risk on the introduction of the two parasitoids. Finally, annual change in age structure of the overwintering generation of U. yanonensis fluctuated more in Amaimi than in mainland Japan because of the winter warmness and the population dynamics of U. yanonensis was not so stable as in mainland Japan. From this fact, it was suggested, the population fluctuation of U. yanonensis was intensified in citrus orchard in mainland Japan when the winter coldness was mitigated as the effect of global warmisation.