Abstract: Nilaparvata lugens (Stal), has two wing-forms, macropterous andbrachypterous. The brown planthopper (BPH) controlled by a pair of dominant genes,and coordinated by hormones excreted by endocrine which is affected by external factors, such as nymphal density and plant nutrients. The sensitive instars of BPH nymph for wing-form development are the Ist - 3rd instars in female and 1st - 5th instars in male respectively. The forewing length of BPH is affected by nymphal density. BPH feeding on rice plants at various stages have dfferent brachypterous ratios, tillering plants cause more brachypterous females than booting rice plants. There are no significant difference between the wing-form development and various BPH biotypes under various nymphal densities. The Zhejiang populations show low brachypterous ratios and have a negative correlation with nymphal density, belonging to the temperate type. The Philippine populations are almost brachypterous, however, the bracheypterous ratio of BPH males raise with the increase of nymphal density. The Guangxi population have a high brachypterous ratio,being similar to the tropical type. The results also indicate that the brachypterous ratios of males are the highest when the nymphal populations are at the medium (54-10 per tiller) or high (＞20 per tiller) densities.

Key words: wing-form development, genetic analysis, sensitive instar, biotypes, BPH population