Pyrethroid-resistant onion thrips, Thrips tabaci Lindeman (Thysanoptera: Thripidae), infesting persimmon fruit

Abstract

A total of 53 strains of onion thrips, Thrips tabaci Lindeman, were established, of which 14 strains were collected from persimmon fruit and 39 strains from a vetch weed, Vicia angustifolia, in commercial persimmon orchards in Wakayama Prefecture. Susceptibility to insecticides was evaluated by the Petri dish-spraying tower method. Pyrethroid-resistant strains and pyrethroid-susceptible strains of T. tabaci were found in persimmon fruit. The LC₅₀ values of cypermethrin and fluvarinate of the pyrethroid-resistant strain were >240 ppm and >800 ppm, respectively, with resistance ratio of >200; however, no significant differences were observed between the two strains in the susceptibility to the other five insecticides, including organophosphates and neonycotinoids. There was a wide range of variability in mortality from 1.1 to 100% caused by cypermethrin at 60 ppm (LC₅₀ values from 0.390 ppm to 177 ppm) in T. tabaci collected from vetch in 5 different persimmon orchards. Regional difference was detected in the proportion of the pyrethroid-resistant strain: up to 67% of the strains collected from Naga where some orchards had been heavily applied with pyrethroids, compared to 17% of the strains collected from Kawahara where organophosphates and neonycotinoids had been applied.