润州黄色杆菌对甜菜夜蛾的毒力及其与 斑痣悬茧蜂寄生的互作关系 摘 要 甜菜夜蛾(Spodoptera exigua Hübner)是农作物的重要害虫之一。由于其抗药性或耐药性强，许多常规的化学农药均不能达到防治目的。应用昆虫病原微生物和天敌防治害虫,是害虫生物防治的两个重要方面,而对它们之间的关系以及共同作用的方式缺乏必要的了解。随着生物防治的研究内涵逐渐扩大，人们开始致力于协调昆虫病原微生物和天敌昆虫控制目标昆虫的研究。 本文测定了润州黄色杆菌(Flavobacter runzhou gen. nov., sp. nov. ,GXW15-4)对甜菜夜蛾幼虫的致病力，观察斑痣悬茧蜂（Meteorus pulchricornis Wesmeal）对感病寄主的选择行为，并测定了该寄生蜂传播细菌的可能性。研究结果对于开发利用润州黄色杆菌，协调利用天敌昆虫斑痣悬茧蜂，具有一定的参考价值。主要结果如下： 1. 测定了润州黄色杆菌制剂对甜菜夜蛾不同虫龄幼虫的毒力 采用浸叶法进行了润州黄色杆菌(Flavobacter runzhou gen. nov.,sp. nov ,GXW15-4)菌株对甜菜夜蛾的毒力测定结果表明，该菌对甜菜夜蛾低龄幼虫有较强的致死率，1～4龄幼虫3d后的感病死亡率分别为96.15%、80.00%、67.86%和67.86%，致死中浓度分别是3.93.×106孢子/ml，6.34×106孢子/ml，8.59×106孢子/ml，1.02×107孢子/ml，随着浓度提高，毒力明显增强。 2. 明确了斑痣悬茧蜂对感染润州黄色杆菌与BT的寄主幼虫的选择性 室内观察了斑痣悬茧蜂（Meteorus pulchricornis）对甜菜夜蛾（Spodoptera exigua）２、３、４龄期健康与感病幼虫的选择行为。实验结果表明，寄生蜂对不同处理的寄主表现一定的选择性，对感病的寄主一定的识别能力。寄生蜂首次敲打次数和首次刺扎次数在健康与感病幼虫间没有显著差异；3h观察期内的总敲打次数和总刺扎次数在健康与感病幼虫间表现出一定差异。 3. 试验观察了斑痣悬茧蜂传播润州黄色杆菌的表现 将甜菜夜蛾3龄幼虫在感病后第3天供寄生蜂寄生，观察到产卵器刺扎后再提供健康寄主幼虫供寄生蜂寄生。结果表明，被寄生蜂幼虫的死亡率很低（＜13%）, 而且原带菌寄主幼虫的感病时间长短（1，2，3 d）之间在健康幼虫被寄生后的存活上没有明显差异。说明寄生蜂寄生行为几乎不传播细菌。 4. 观察了润州黄色杆菌对被寄生后的幼虫存活的影响 将3龄幼虫在寄生后于第1d和3d分别感染润州黄色杆菌（菌液的1600倍），观察幼虫存活情况。实验结果表明，感染4后的死亡率显著高于对照，感染4d后的死亡率存在显著差异，死亡率达到70%，感染5d后达到86%。 关键词：甜菜夜蛾；斑痣悬茧蜂；润州黄色杆菌；毒力；寄生；病菌传播；，寄主选择；生物防治

TOXICITY OF BACTERIUM FLAVOBACTER RUNZHOU TO SPODOPTERA EXIGUA LARVA AND ITS INTERACTION WITH PARASITISM BY METEORUS PULCHRICORNIS ABSTRACT The beet armyworm Spodoptera exigua (Hübner) is a polyphagous pest on numerous crops over the world. Biological control can be an effective approach to the persistent management of this noxius pest. Parasitoids and pathogens are two important groups of natual enemies that provide potential for the biocontrol. To develop an effective management design for control of the beet armyworm, we conducted a series of experiments about the toxicity of the bacterium, Flavobacter runzhou gen. nov., sp. nov., GXW15-4, the host selection of the parasitoid Meteorus pulchricornis Wesmeal between healthy and pathogen-infected larvae. The main results were summarized as following. 1. Toxicity of the bacterial formulation of Flavobacter runzhou to Spodoptera exigua larvae The bacterium, Flavobacter runzhou, is a recently found insect pathogen that infects numerous lepidoterous larvae. The virulence of the pathogen against larvae of the beet armyworm, Spodoptera exigua Hübner (Noctuidae, Lepidoptera) was evaluated by the leaf-dip method. The pathogen caused higher mortalities to young larvae than to old larvae, with the cumulative mortality at three days after the initial infection was 96.15% for the first instar, 80.00% for the second, 67.86% for the third, and 67.86% for the last instar larvae respectively; at four days after the initial infection mortality of the first instar larvae was 100%, that of the 2nd to forth instar larvae was ca. 90%. The LD50 was 3.93×106 cfu/ml for the first instar, 6.34×106 cfu /ml for the second, 8.59×106 cfu /ml for the third, and 1.02×107 cfu /ml for the last instar larvae. The LT50 to same instar larvae was reduced with the concentration of the pathogen formulation, while it was extended with increase of larval instars at the same concentration of the pathogen formulation. 2. Host preference of Meteorus pulchricornis between healthy and infected larvae by two bacteria The paired-choice was used to observe the selection behavior of the parasitoid Meteorus pulchricornis between healthy and infected 2nd to 4th instar larvae by Bt and F. runzhou. The number of first antenna-tapping and first ovipositor-drilling did not differ significantly between healthy and pathogen-infected host larvae. But the number of antenna-tapping and of ovipositor-drilling during three-hour observation period was different, to some extent, between healthy and pathogen-infected host larvae. 3. The pathogen-transmission of Meteorus pulchricornis The 3rd instar larva of the beet armyworm, after infected by bacterium F. runzhou, was exposed to parasitism. The wasp that exercised ovipositor-drilling was then exposed to a healthy host larva, which was observed for survival. The larvae exhibited low mortality, whether the infection time of previous host larvae was short or long, which suggested little transmission of the parasitoid through oviposition. 4. Survival of parasitized host larvae when infected by bacterium F. runzhou The 3rd instar larva, one and three days after being parasitized by Meteorus pulchricornis, was infected by the bacterium F. runzhou, and was observed in survival. The results showed that the mortality of treated larvae was significantly higher than that of the control after four days of infection by 70%, and after five days of infection by 86%. KEY WORDS: Flavobacter runzhou; Spodoptera exigua; Meteorus pulchricornis; toxicity; parasitism; host selection; pathogen transmission; biological control