Effect of insecticide application on the population density of yellow tea thrips, Scirtothrips dorsalis Hood (Thysanoptera: Thripidae) and Euseius sojaensis (Ehara) (Acari: Phytoseiidae) on grapes

The insecticide susceptibility of yellow tea thrips, Scirtothrips dorsalis and its natural enemy mite, Euseius sojaensis was evaluated at 25 deg C under 16L8D. Imidacloprid was highly effective against S. dorsalis second instar larvae. Permethrin was effective at 100-200 ppm and marginally effective at 25-50 ppm. Imidacloprid was not harmful to E. sojaensis female adults, while permethrin was seriously harmful. The effect of insecticide application on the population of S. dorsalis and E. sojaensis was investigated in a Delaware vineyard in Osaka Prefecture. With the application of imidacloprid the density of S. dorsalis was effectively reduced and E. sojaensis was found to survive on the grapes. In contrast, the density of S. dorsalis was slightly reduced and E. sojaensis was not found on the grapes with the application of permethrin. Injury to fruit by S. dorsalis was significantly lower on grapes with imidacloprid application. The results suggest that imidacloprid did not seriously affect the population of E. sojaensis but shows good control against S. dorsalis on grapes.