摘要
三化螟幼虫在晚粳稻分孽、园杆、孕穗、破口期均能侵入，所形成的总受害株数、受害株类型和幼虫存活率与生育期密切相关。分蘖期引起的受害丛率、受害株率和损失率与卵块密度呈正显著相关，单个卵块平均损失稻谷（５９．１１±２．９９）ｇ；孕穗至破口期则损失（７４．５８±３．３１）ｇ。考种结果表明，产量损失的主要原因是有效穗减少。在现有生产条件下，三化螟经济允许卵块密度为：分蘖期每公顷１９５０～２２５０块，孕穗至破口期每公顷１５００～１８００块；防治指标为：分蘖期每公顷１５００～１６５０块，或为害团每公顷７５０～９００个，为害丛率２％～３％，为害株率１％～５％。
Abstract The YSB￣② larva could feed inside the stem at the tillering,panicle initiation, bootingand heading stages in late Keng rice,the numbers and types of infested plants,and survival rates oflarva exhibited highly correlation with the rice growth stages. At the tillering stnsre. the rates ofinfested plants and hills ,as well as yield loss were significantly correlated with egg-mass densities.The mean grains loss caused by a single egg-mass stages. at tillering and booting heading were(59.11±2. 99) g and ( 74. 58 ± 3. 31 ) g .respectively. The results of yield component analysis indi-cated that the maior factor of yield loss was the reduction of fertile panicles. According to the pre-sent conditions for rice production,the economically bearable injury caused by YSB were estimatedabout 1 950～2 250 and 1 500～1 800 egg-masses per ha at tillering and booting-heading stages.The control thresholds at the tillering stage were 1 500～1 650 egg-masses or 750～900 damagedhills perhectare,or 2～3 percent infested hills ,or 1～5 percent infested plants.Key wotds yellow stem borer; late Keng rice; dynamics of invasion and survial; grain loss;control threshold
基金
浙江省科委科学基金
