稻螟赤眼蜂对二化螟和稻纵卷叶螟不同产卵行为的适应机制

Feeding and oviposition of herbivores can trigger volatiles emission of plants called herbivory-induced plant volatiles (HIPVs), which can help parasitoids to locate their hosts. Trichogramma japonicum is a dominant egg parasitoid species against two rice pests, the rice stripped stem borer (SSB), Chilo suppressalis Walker, and rice leaf folder (RLF), Cnaphalocrocis medinalis Guenée. Previous studies showed that the female moths of SSB preferred to lay eggs on healthy rice plants, while RLF have no preference for oviposition on larvae damaged or healthy rice plants. However, it is unclear how the T. japonicum accurately locates two different hosts. Based on these, the project intends to study that: 1) the “Y” olfactometer is used to determine the preference of T. japonicum for rice volatiles induced by larvae damage or female oviposition of SSB and RLF; 2) Gas chromatography-mass spectrometry (GC-MS) is used to analyze the components and contents of volatiles in different rice treatments; 3) the electroantennography (EAG) is used to screen the active components form rice volatiles, which can elicit electrophysiological responses of T. japonicum, and behavioral responses of T. japocicum to standards of active compounds; 4) the experiment on the parasitization rate of SSB or RLF eggs by T. japonicum is conducted in cages in the greenhouse. This study will explain how T. japonicum can locate the two hosts accurately, and elucidate the biochemical mechanism. The results are expected to enrich the theory of interactions of rice, pest, and natural enemy, and provide a scientific basis for the prevention and control of SSB and RLF using T. japonicum, efficiently and rationally.

植食性昆虫取食和产卵行为会诱导植物产生HIPVs，寄生蜂依赖HIPVs进行寄主定位。稻螟赤眼蜂是水稻害虫二化螟、稻纵卷叶螟的优势卵寄生蜂。前期研究发现：二化螟雌蛾会逃避其幼虫为害稻株，偏爱在健康稻株上产卵；稻纵卷叶螟雌蛾不受其幼虫为害影响。稻螟赤眼蜂如何精确定位两种不同寄主尚不清楚。基于此，本项目拟采用“Y”型嗅觉仪测定稻螟赤眼蜂对二化螟(稻纵)幼虫取食或雌蛾产卵诱导的水稻挥发物偏好性；利用气质联用仪(GC-MS)分析不同处理水稻挥发物组分及含量，采用触角电位(EAG)筛选对稻螟赤眼蜂有电生理活性的组分，并验证稻螟赤眼蜂对活性组分标准品的趋性；罩笼试验研究不同处理水稻对稻螟赤眼蜂寄生率的调控。最终阐明稻螟赤眼蜂利用水稻HIPVs对不同产卵行为的二化螟和稻纵卵进行精准定位的能力及生化机制，以期丰富水稻-害虫-天敌互作关系理论，为研究水稻抗虫性及水稻害虫绿色防控提供新思路和策略。

卵寄生蜂通常利用植物挥发物和卵本身挥发物对寄主卵进行定位。稻螟赤眼蜂是水稻害虫稻纵卷叶螟的优势卵寄生蜂，常被用于田间释放进行生物防治。在稻田复杂的气味环境中，稻螟赤眼蜂如何定位稻纵卷叶螟卵？卵诱导挥发物是否在卵寄生蜂对卵进行精确定位时发挥了重要作用？本研究以水稻-稻纵卷叶螟-稻螟赤眼蜂三级营养关系为研究体系，明确稻螟赤眼蜂如何识别不同发育时期的稻纵卷叶螟卵。结果发现：稻螟赤眼蜂对稻纵卷叶螟不同日龄卵诱导稻株选择反应不同，带有2日龄卵的稻株(2日龄卵稻株）对稻螟赤眼蜂有显著地吸引作用，1日、3日、4日龄卵稻株没有作用，同时在2日龄卵稻株上的寄生率最高，明确了2日龄卵稻株对稻螟赤眼蜂有吸引作用。收集不同处理稻株挥发物进分GC-MS分析显示，不同日龄卵诱导稻株释放地挥发物存在组分和含量上的差异。共筛选出了6种差异化合物(2,4-dimethyl-1-heptene，α-pinene，3-carene，D-limonene，o-cymene，butylated hydroxytoluene)。对差异化合物功能进行验证发现，α-pinene 在4 ng/μL和10 ng/μL浓度下对稻螟赤眼蜂有显著的吸引作用，其它5种化合物对稻螟赤眼蜂没有作用。稻螟赤眼蜂更喜欢1日龄稻纵卷叶螟卵，与2日龄有显著性差异。但是，稻螟赤眼蜂寄生在1日和2日龄卵上的稻螟赤眼蜂发育历期、羽化率和雌虫率均没有显著性差异。综上所述，我们认为，稻纵卷叶螟产卵可以诱导水稻释放对稻螟赤眼蜂有吸引作用的化合物，稻螟赤眼蜂在田间对稻纵卷叶螟卵进行寄主定位时，主要是依靠卵诱导的植物挥发物，且与卵诱导时间有关。