The bionomics of Chilo suppressalis larvae overwintering in paddy-rice and water-oat fields were investigated in Beijing (China) in early-winter (middle November) and after-winter (early March). The overwintering larvae were 4th instar or older, and the 6 instar ratio in water-oat fields was 17.5% higher than that in paddy-rice fields in early-winter. The old larvae accounted for a higher percentage in after-winter than in early-winter. Female to male larvae ratios were respectively 1:2.0 and 1:1.7 in early-winter and after-winter in paddy-rice fields, and 1:1.4 and 1:1.2 in water-oat fields. Larvae duration was longer in early-winter than after-winter, and not significantly different between paddy-rice and water-oat fields in one period. However, larvae from water-oat fields took 14.0% more time before pupation than that from paddy-rice fields in early-winter, while larvae and pupa from water-oat fields were significantly heavier than those from paddy-rice fields. Mortality rate of larvae collected in early-winter was greater than 65%. Fungi infection was the primary mortality factor in water-oat fields (i.e. over 90% total mortality), while parasitic wasp and bacteria infection constituted the primary mortality factors in paddy-rice fields (i.e. respectively, over 50% and 25% total mortality). Apanteles chilonis [Cotesia chilonis] and Eriborus terebrans [Diadegma terebrans] were the 2 dominant parasitic wasps.
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