Suppressive effect of orius sp. (hemiptera: Anthocoridae) on the population density of thrips palmi karny (thysanoptera: Thripidae) in eggplant in an open field

Abstract

Effect of predation by Orius sp. on the density of Thrips palmi KARNY on eggplant in an open field was estimated by the insecticidal check method. Orius sp. was controlled by application with fenthion (500ppm, emulsion). On eggplant untreated with fenthion, the population density of thrips reached high density levels in July and September. In the first peak, the thrips population included a high density of two native species (Thrips setosus MOULTON and Mycterothrips glycines (OKAMOTO) and a low density of T. palmi, whereas in the second peak T. palmi was dominant. The population density of Orius sp. also reached its peaks in July and September. The population trend of Orius sp. seemed to synchronize with that of thrips. The first incidence of adult T. palmi on eggplant was in late June. The population density of adult T. palmi on eggplant treated with fenthion increased from the middle of July, whereas the population without treatment remained at a low density level until early August. The maximum density of T. palmi on the plants treated with fenthion was four times as large as that on the untreated plants. Moreover, until the middle of September the percentage of eggplant fruit injured by T. palmi in the plot without treatment was lower than that in the treated plot. It seemed that the high density of Orius sp. in July and early September suppressed the T. palmi population density and fruit injury. © 1990, JAPANESE SOCIETY OF APPLIED ENTOMOLOGY AND ZOOLOGY. All rights reserved.