Abstract
The effects of isoprothiolane fungicide, diisopropyl-1, 3-dithiolan-2-ylidenmalonate, on the longevity and fecundity of brown planthoppers were examined under laboratory conditions. The adults and nymphs of planthopper were fed rice seedlings treated with an aqueous solution of isoprothiolane (IPT) by the root dipping method. The adults fed with 40ppm treated seedlings throughout the stage had shorter lives, especially males, and less oviposition but a normal preoviposition period compared with untreated adults. The eggs laid by treated females showed lower hatchability than the eggs of untreated females. However, the eggs laid by females treated for a shorter period (7 days) hatched normally and the nymphs showed normal growth and development to adult emergence when reared with untreated seedlings. The nymphs reared with treated seedlings from the first instar stage slowly died in the third to the fifth instar stages; death frequently occurred at moulting. The adults emerged from nymphs fed with 5ppm treated seedlings throughout the nymphal stage showed decreased longevity in comparison to untreated adults and the number of eggs laid decreased considerably. Little effect on egg hatching was observed when rice seedlings oviposited by untreated planthoppers were treated with IPT; hatched nymphs showed normal growth and development to emergence.
