Comparison of thermal tolerance of seven native species of parasitoids (Hymenoptera: Eulophidae) as biological control agents against Liriomyza trifolii (Diptera: Agromyzidae) in Japan

The efficiencies of seven native species of eulophid parasitoids (Pnigalio katonis, Hemiptarsenus varicornis, Diglyphus isaea, D. minoeus, D. pusztensis, Chrysocharis pentheus and Neochrysocharis formosa) as biological control agents against Liriomyza trifolii in a greenhouse were evaluated based on their thermal tolerance in development and reproduction. All of them are solitary and idiobiont parasitoids, and their adults kill hosts directly by feeding on the hosts. Based upon their thermal tolerance, the species could be roughly classified into two groups, i.e., H. varicornis and N. formosa which are more adapted to high temperatures, and the other five species which are more adapted to low temperatures. In biological control, host killing by host-feeding is profitable in the release step, but becomes unprofitable in the mass-production step because it does not result directly in production of progeny. Hence, an evaluation method based on biological control efficiency (BCE) is proposed in this study as a comprehensive criterion for evaluating the efficiency of the parasitoids as biological control agents. The thermal tolerance and BCE clarified in this study revealed that D. isaea should be used in cool seasons and N. formosa in hot seasons, based on a borderline temperature of 20 to 25°C in the greenhouse.