Effects of a New Juvenile Hormone Mimic, NC-170, on Metamorphosis and Diapause of the Small Brown Planthopper, Laodelphax striatellus

Abstract

Effects of a new jevenile hormone mimic (JHM), NC-170 [4-chloro-5-(6-chloro-3-pyridylmethoxy)-2-(3, 4-dichlorophenyl)-pyridazine-3(H)-one], on the metamorphosis and diapause of the small brown planthopper were examined in comparison with those of Juvenile Hormone (JH)-1, 2 and 3. NC-170 had a strong metamorphosis-inhibiting activity with a ID₅₀ of 0.42pg/larva when topically applied to nondiapause mid-4th stadium larvae. The three JHs showed no signs of metamorphosis inhibition not only by single topical application to mid-4th stadium larvae at a maximal dosage (300ng/larvae), but also by daily repeated topical applications to larvae in the early 4th to 5th stadium (30ng/day/larva). When the planthoppers were reared at 20°C under short-day (8L/16D) photoperiods throughout the embryonic and larval stages, the development was considerably retarded in the 4th larval stadium, which is apparently the state of diapause. They resumed normal (nondiapause) development when 20-hydroxyecdysone was topically applied. Contact applications of 100ppm NC-170 through the larval stage prevented larvae from entering diapause, and topical applications of the chemical terminated diapause and induced 4th larval molts about 8 days after treatment. JH-1 also terminated diapause in the same manner at the same dosages as NC-170.