16 Biological Control of Diamondback Moth

The diamondback moth, Plutella xylostella (L), is recognized as a widely distributed and serious pest of crucifers in many countries. In some countries, however, it is effectively suppressed by parasites. These are critically examined as are the various attempts to import parasites and to release them. The appraisal reveals that the parasites of P. xylostella are a valuable control component and resource. Though numerous parasite species exist, not all are found to be effective. On the contrary, the key ones are restricted to only a few species and these belong largely to the genera Diadegma, Apanteles, and Microplitis. Except for Diadegma eucerophaga and possibly Diadegma fenestralis, none appears capable of exerting full control by itself. Many countries are still continuously plagued by P. Xylostella and there is strong evidence that this is due to the lack of crucially important parasites. Unless the relevant key species are made a part of the host-parasite complex, these problems are likely to persist. On the other hand, abandoning them will condemn crucifer cultivation to continued drenching in ever-increasing amounts of insecticides. These conclusions seem inescapable as all known cases of successful P. xylostella control have been obtained only when the basic control component constitutes either parasites or chemical insecticides.