Abstract: Imidacloprid, a nitromethylene analog1-(6-chloro-3-pyridylmethyl )N-nitroimidazolidin-2-ylideneamine, is a highly effective systemic insecticide,against the brown planthopper, Nilapavarta lugens (Stal), (BPH), as shownboth in laboratory and field tests. The LD₅₀ of Imidacloprid (technicalImidacloprid>96%) for contact activity against the 3rd and the 5th instarnymphs of BPH was 2.55 x 10^-5μg/nymph and 6.78 x 10^-5μg/nymph respectively.Regressions of mortality probit (Y) against logl0 of contact concentration (X) of the 3rd and the 5th instar nymphs were Y=5.6231+1. 0486X and Y=5. 2091+1.2389X respectively. Imidacloprid did not show only as a highly contact insecticide but also an excellent stomach toxicant against young and mature nymphs and adults of BPH. Field trials of foliar application in paddy fields of Jurong and Wujiang Counties with 10% Imidacloprid WP, at a rate of 15 or 30g a.I./hm².Against BPH, achieved stably high (>90% control effectiveness) population sup pression over 40 days after treatment. The high insecticidal fficacy withImidacloprid as foliar spray for BPH control in paddy fields was basically manifested into three effective aspects, including rapidity (1～3 days after treat ment),sustainability (4～10 days of treatment) and long residual effect (11 days after treatment). The field trials with Imidacloprid also displayed good selectivity between BPH and its natural enemies. It was specially safe to spider community in paddy fields.

Key words: Imidacloprid, brown planthopper, bioactivity, control effectiveness