寄生蜂定位致瘿害虫的化学机制研究——以孟氏胯姬小蜂为例

Gall-inducing insects live within plant tissues and induce tumor-like growths that provide the insects with food, shelter, and protection from natural enemies. However, these insects can precisely targeted by parasitoids. Chemical mechanism for host location by parasitoids of gall-inducing insects has not been answered. Leptocybe invasa is a global invasive pest in Eucalyptus plantations native to Australia. Quadrastichus mendeli is an obligate parasite attacking L. invasa larvae to effectively control its natural population of invaded regions in the world. Therefore, Q. mendeli is a perfect species to explore the chemical mechanism for host location by parasitoids of gall-inducing insects. In this study, temporal emission of plant volatiles of galls at different developmental stages induced by L. invasa, behavior response of Q. mendeli to these plant volatiles of galls, and binding characteristic of odorant binding proteins genes with these plant volatiles of galls will be conducted using the techniques of GC-MS, GC-EAD, RT-PCR, RACE et al. Results could provide essential information to establish the model system for studying the host location by parasite of gall-inducing organisms, to reveal the co-evolutionary interactions among plant, gall-inducing organisms and parasite, and to improve the potential control ability of parasitoids against gall-inducing insects.

致瘿害虫营高度隐蔽的生活方式，但并不影响寄生蜂的精确定位。然而，寄生蜂精确定位致瘿害虫的化学机制尚不清楚。桉树枝瘿姬小蜂Leptocybe invasa是桉树上的一种入侵性致瘿害虫，孟氏胯姬小蜂Quadrastichus mendeli是仅寄生桉树枝瘿姬小蜂幼虫的专性寄生蜂，控害效果明显。本项目以孟氏胯姬小蜂为材料，利用GC-MS、GC-EAD、RT-PCR和RACE等化学分析、电生理和分子生物学技术，弄清桉树枝瘿姬小蜂寄主虫瘿不同发育阶段特异性挥发物的时序变化，研究其对桉树枝瘿姬小蜂虫瘿不同发育阶段特异性挥发物的行为反应，明确其触角气味结合蛋白基因与虫瘿活性挥发物的结合特性，解析虫瘿不同发育阶段特异性挥发物在孟氏胯姬小蜂寄主定位中的化学机制。结果为研究寄生性天敌定位致瘿生物提供模式系统，有助于揭示植物-致瘿生物-寄生性天敌间的协同进化关系，有利于提高寄生蜂对致瘿害虫的控害潜能。

致瘿害虫营高度隐蔽的生活方式，但并不影响寄生蜂的精确定位。本研究以桉树—桉树枝瘿姬小蜂—孟氏胯姬小蜂为模式系统，明确了寄生蜂孟氏胯姬小蜂精确定位致瘿害虫桉树枝瘿姬小蜂的化学信息感受机制。研究发现，桉树枝瘿姬小蜂为害桉树后，诱导形成了很多不同种类的植物挥发物。孟氏胯姬小蜂对桉树枝瘿姬小蜂为害桉树后诱导释放的3-蒈烯、对伞花烃、4-异丙烯基甲苯和对乙基苯乙酮4种活性挥发物单物质或混合物均有明显的触角电生理反应和定向趋向行为反应。明确了孟氏胯姬小蜂产卵器上4种不同类型的微毛感器、2种不同类型的刺形感器和1种钟形感器的大小和分布。孟氏胯姬小蜂触角含有216个化学感受基因（包括7个化学感受蛋白基因、24个味觉受体、68个离子型受体基因、59个气味结合蛋白基因、34个气味受体基因和24个感觉神经元膜蛋白基因），且明确了QmenOBP2主要在头部表达，QmenOBP3、QmenOBP4、QmenOBP5、QmenOBP7主要在触角中表达，QmenOBP6和QmenOBP8主要在胸部表达，QmenOBP9主要在腹部表达。经原核表达载体的构建，蛋白的表达、纯化得到了QmenOBP2。荧光竞争结合实验结果表明，QmenOBP2与醇类、酮类、醛类、烯类和苯类均具有结合能力（Ki<50μM），其中其与桉叶油醇和反式-β-罗勒烯结合能力最强（Ki < 20μM）。分子对接结果显示，QmenOBP2与反式-β-罗勒烯结合的自由能最低，为-7.952 kcal/mol，对接后的复合物最稳定；与3-蒈烯、对伞花烃、4-异丙烯基甲苯、双戊烯和对乙基苯乙酮的自由能分别为-7.714、-7.401、-7.319、-7.257、-7.148 kcal/mol，对接后复合物的稳定性依次减弱。研究结果明确了孟氏胯姬小蜂寄主定位的化学信息感受机制，其为揭示植物-致瘿生物-寄生性天敌间的协同进化关系提供了模式系统，及利用虫瘿挥发物提高寄生蜂对致瘿害虫的控害潜能提供了数据支撑，具有重要的理论和实践价值。