Overwintering mortality of the apple snail, Pomacea canaliculata was investigated in a paddy field of Southern Japan for seven consecutive years. Field data and laboratory experiments revealed snails larger than 6.0 mm exhibited higher cold tolerance than small snails. Seven-years of field data showed that a linear regression explained a close relationship between the overwintering mortality of snails larger than 6.0 mm and the cumulative low temperature calculated as the subtraction of the hourly temperature from 10°C (CLT). A high correlation was also observed between overwintering mortality of snails and the mean temperature between December and February. Thus, temperature data seems to be practical and effective in estimating mortality of field snails during the winter.

Fluctuations in the wing-form ratio of the brown planthopper (BPH), Nilaparvata lugens, were examined by collecting fifth-instar nymphs from rice fields. Two peaks of brachypterous females were observed at 40-50 days after transplanting (DAT) and 75-85 DAT (5 days before heading-10 days after heading). After 75-85 DAT, the percentage of brachypterous females decreased with an increase in BPH density. However, the BPH density was still low after 40-50 DAT when the first decrease in the percentage of brachypterous females occurred. Thus, not only population density of BPH, but also the rice plant stage seems to affect the fluctuations in female wing-form ratio. The SPAD readings of rice leaf, which are associated with leaf nitrogen content, fluctuated with rice plant stage and showed two peaks at 30-50 DAT and 65-80 DAT. The fluctuation pattern of the SPAD readings was similar to that of the percentage of brachypterous females. This suggests that the percentage of brachypterous females fluctuated in accordance with a decrease in nitrogen content of rice plants.

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Relationships between seasonal fluctuations in pheromone trap catches of Spodoptera litura F. (Lepidoptera: Noctuidae) and the number of soybean leaves newly injured by young larvae of this species were examined in soybean fields from 1999 to 2002 in Saga Pref., Japan. In soybean fields sown in July, a small peak of injured leaves occurred in mid to late August and a large peak occurred in mid to late September. In most cases, the pheromone trap catches and occurrence of injured leaves exhibited similar trends with both peaks occurring almost simultaneously (Ϯ3 days) in mid to late September. This suggests that not only a prominent increase in soybean leaves injured by young larvae, but also a prominent increase in pheromone trap catches are useful information to determine a precise timing of control. On the other hand, the timing of control seems to be difficult to predict using the effective accumulative temperature of this species.

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