Abstract
The activity of a new juvenile hormone analogue, NC-170 [4-chloro-5-(6-chloro-3-pyridylmethoxy)-2-(3, 4-dichlorophenyl)-pyridazin-3(2H)-one], was evaluated on four species of leafhoppers, Nephotettix cincticeps, N. nigropictus, N. virescens and Recilia dorsalis. When NC-170 was topically applied to mid-penultimate larvae, their metamorphosis was strongly inhibited. The compound with the ID50's of 5.2×10-11 to 3.7×10-12g/larva was 10 to 30 times as active as natural JH-1. The critical period of the morphogenetic activity was limited in a 24hr span before and after the 4th larval molt. The affected insects did not develop into normal adults, but into supernumerary larvae (SL1). About 5 days later, the SL1 could not complete the molt into secondary supernumerary larvae (SL2) and subsequently died. Furthermore, NC-170 showed good sterile effects. When newly emerged female N. cincticeps adults were continuously exposed to NC-170, the hatchability of oviposited eggs severely reduced, even at a concentration of 4ppm. In a field trial, NC-170 showed good foliar persistency in paddy fields and single spray treatment with 100ppm NC-170 considerably suppressed the population density of N. cincticeps for more than 6 weeks.
