The occurrence of Leptocorisa oratorius in weedy sites of farmers' paddy fields was investigated in reference to the adult-nymphal structure and ovarian development in female adults. Results indicated that nymphal development takes place in paddy fields before rice flowering when the fields were infested with adults whose ovaries had already matured by feeding on panicles of weeds or early-flowering rice plants. It is thus considered that weed control should be emphasized to eliminate panicle-bearing weeds in and around paddy fields before the onset of rice flowering so as to prevent advanced ovarian maturation in the adult populations which immigrate into paddy fields to lay eggs. Synchronous rice cropping is also essential for the same purpose.