嗅觉介导的单食性天敌寄主识别及转移风险的研究

Host shift is the key important criterions of evaluation of biocontrol agent of invasive plants. Recently, some biocontrol agents have been reported to impact non-target plants. However, few were known about host shift initialed by olfactory, as the first step, cues underlying host preference of the phytophagous insects in the context of habitat isolation. The flea beetle, Agasicles hygrophila, is a monophagous bio-control agent which has been documented for successful managing the invasive weed Alternanthera philoxeroides around world. Our previous studies have further confirmed its monophagy by evaluation of its responses to more than 30 non-target plant species. The present project used "A. hygrophila- A. philoxeroides" as the research model. The solid-phase micro-extraction method and the headspace method are each used to extract volatiles from host plants, relatives, and non-host plants, respectively. Isolation and identification of different treatment compounds released by healthy plants, artificially damaged, and insects-feeding plants will be conducted with GC-MS. GC-EAD, and Y-tube olfactometric assays will be used separately to test electrophysiological and behavioral responses (attraction or repellent) of A. hygrophila to the extracted volatiles, a single and mixed standard compounds, respectively. Finally, the behavioral experiments in the field will be conducted to verify the key compounds for host-specific recognition of A. philoxeroides. This study help better understanding the interspecfic relationship between monophagous insects and their host plants from a viewpoint of chemical ecology. By exploring utilization of specific chemical information recognition mechanism, the study can reduce potential ecological risk of candidate natural enemies due to host shift from target plants to non-target plants. Therefore, the study may provide new thinking for the corevolution between plants and herbivores.

引进天敌是否发生寄主转移是评价入侵杂草生防效果的一项重要标准。近年来生防作用物攻击非靶标物事件频发，而在寄主转移过程中，引起植食性昆虫选择偏好性的第一步—嗅觉作用鲜见。莲草直胸跳甲是世界上引种并成功控制入侵种喜旱莲子草的专食性天敌，前期研究明确了其单食性及对30余种有典型代表的非靶标植物的偏好性。本项目以“莲草直胸跳甲—喜旱莲子草”为模型，采用固相微萃取、顶空吸附剂法收集，GC-MS分离与鉴定寄主植物、近缘种、非寄主植物在健康、伤诱及跳甲取食后的挥发物，用GC-EAD、嗅觉行为仪研究跳甲对挥发的混合物、单一标准化合物的电生理反应和行为趋性（吸引与驱避），结合田间行为确定跳甲专性识别的关键化合物，用化学生态学来阐释专食性昆虫与寄主间的种间关系，探索利用专性化学信息识别加强检测天敌的寄主专一性，以降低候选天敌对非靶标植物发生寄主转移的生态风险，也有助于了解单食性昆虫与植物的协同进化。

喜旱莲子草Alternanthera philoxeroides (Mart.) Griseb属苋科Amaranthaceae，莲子草属Alternanthera，是一种世界性的恶性杂草。莲草直胸跳甲 (Agasicles hygrophila，Selman and Vogt) 属鞘翅目Coleoptera，叶甲科Chrysomelidae，跳甲亚科Halticinae，是喜旱莲子草最有效的生防天敌昆虫。植物挥发物是影响昆虫行为的重要物质，而昆虫利用嗅觉感受植物挥发性从而进行寄主的定位、取食和交配等行为。研究专食性昆虫莲草直胸跳甲与喜旱莲子草的生防作用物，利用跳甲的寄主植物和非寄主植物进行研究，发现跳甲感应植物挥发物的特异性比例来寻找定位寄主植物。重要结果如下：.1.通过测定田间莲草直胸跳甲对 13 种不同供试植物的偏好性。聚类分析结果显示: 跳甲偏好选择寄主和喜旱莲子草，取食寄主植物最大面积为 59.50 ± 4.62 mm2，取食莲子草为 46.50 ± 3.69 mm2。田间交配后的雌虫在寄主植物和莲子草叶片上产卵量分别为 194.00 ± 10.58／每株和12.33 ± 1.20／每株。卵块在莲子草上的孵化率在 50 %以上。.2.鉴定出五种主要的植物挥发物。其中 DMNT是对分类贡献最大的化合物。D 是释放最多且VIP值最大的化合物 (VIP＝1.56)。.3.电生理检测发现，跳甲雌虫和幼虫取食后，植物释放物D对触角的活性最强。跳甲触角对(E)-2-hexenal，(Z)-3-hexenyl acetate, (E)-3-hexenol 和 Z 表现出了很强的电位反应。在Y管实验发现，雌虫对20 ng的D表现出更强的趋性。而 Z在10 ng时，对雌虫产生了强烈的驱避反应。.4.将Z添加到喜旱莲子草的植株，雌虫偏好率下降。对非寄主植物苋菜添加D 后，雌虫的选择率升高。混合配比D : Z = 99 : 1，雌虫偏好显著。D : Z = 1 : 1时，雌虫驱避反应强烈。当Z为可变的化合物时，对雌虫驱避作用显著。这种效应在田间实验中具有相似的结果。.本研究发现专食性昆虫可以依靠嗅觉识别寄主与非寄主植物的挥发物形成的特殊比例来寻找定位寄主植物，这种机制及其方法对生物防治过程中所产生的寄主选择和寄主转移风险与评估具有潜在的科学与应用价值。