水稻大螟在宁波专区各县每年都普遍发生,尤其在镇海县、宁波市、鄞县、奉化县等县(市)的奉化江一带水稻地区为害更重。大螟一年发生4代,各代都要为害水稻。第一代大螟为害水稻盛期在5月下旬至6月上旬,造成早稻枯心苗,特别是早栽早稻田埂附近1～5行的水稻受害更严重,个别田被害率可以高达50%以上;第二代大螟为害盛期在7月中、下旬,造成单季晚稻枯心苗和一部分迟熟早稻白穗;第三代大螟为害盛期在8月中、下旬, Rice Sesamia in every county in Ningbo area occurs annually, especially in the paddy areas of Fenghua River in Zhenhai County, Ningbo City, Yin County, Fenghua County and other counties (cities). Sesamia in four generations a year, all generations should damage rice. The damage caused by the first generation of Sesamia inferens during late May to early June resulted in more serious damage to the early-rice dry seedlings, especially the rice lines 1-5 in the vicinity of the early-cropped paddy fields. The damage rate of individual fields could be as high as 50% or more ; Second-generation Sesamia inophthalmus peak in mid-July, late, resulting in single-season late rice and some late-maturing white spike ear; third-generation borer peak in mid-August, late,