杂草挥发物对棉铃虫天敌中红侧沟茧蜂的寄主寻找定位作用

Microplitis mediator is an important larval endo-parasitoid of various lepidopteran pests, and it has been used as an biocontrol agent for controlling Helicoverpa armigera. Herbivore-induced volatiles from plants are important signals for parasitoids to locate their hosts. The amaranth Amaranthus retroflexus、velvetleaf Abutilon theophrasti are two species of broadleaf weeds in cotton and soybean fields，etc. And they are also the hosts of H. armigera. In a tritrophic system among weed (amaranth and velvetleaf),H.armigera, and parasitoid M. mediator, behavioral responses of M. mediator to herbivore-induced weed volatiles will be investigated by olfactometer assays, and the induced volatiles will be collected and analyzed using Gas chromatography-mass spectrometry (GC-MS) system in lab. Active compounds from weed volatiles eliciting electrophysiological responses of M.mediator will be screened by Gas chromatography-electroantennographic detection (GC-EAD), behavioral responses of M. mediator to synthetic compounds will be tested in lab. Field-testing of synthetic herbivore-induced weed volatiles as attractants for M. mediator will be performed.And the effects of synthetic compounds on parasitism rate of M.mediator will be conducted by field cage study.This study will provide baseline information to develop attractants by appling synthetic compounds for parasitoid and to increase control capability to H. armigera in the field. In addition, this study will help us to make clear the mechanism of host location for parasitiod.

植物在害虫危害后释放的挥发性物质是寄生蜂寻找定位寄主的重要信号物质。反枝苋和苘麻是棉花、大豆等农田阔叶杂草，也是棉铃虫寄主。本项目以杂草（反枝苋和苘麻）-棉铃虫-中红侧沟茧蜂为研究模式，室内采用Y型嗅觉仪测定寄生蜂对不同诱导方式下的两种杂草挥发物的趋性行为反应，利用气质联用系统（GC-MS）分析两种杂草挥发物组份及结构，采用气谱与触角电位连接仪（GC-EAD），筛选对寄生蜂有电生理活性的物质，利用活性物质标样验证寄生蜂对其趋性反应；结合室外大田挂板试验和罩笼试验明确有活性的挥发物对寄生蜂引诱作用和对寄生蜂寄生率的影响。最终明确杂草释放的挥发性物质对寄生蜂寻找定位寄主的作用，为研制对寄生蜂有吸引能力的缓释剂奠定基础，从而提高田间寄生蜂对棉铃虫控制能力，加快探索新的棉铃虫防治策略步伐；有助于理论上明确天敌寻找定位寄主的机理。

植物在害虫为害后释放的特异性挥发性物质是寄生蜂寻找定位寄主的重要信号物质。目前虫害诱导的植物挥发性物质的研究基本是针对农田系统中的几种主要作物如棉花、玉米等。杂草是农田生态系统中一个重要组成部分，也是许多害虫的中间寄主，而对虫害诱导杂草释放的挥发性物质及其对天敌功能研究报道较少。本项目以杂草（反枝苋、苘麻）-棉铃虫-中红侧沟茧蜂为研究模式，系统研究了中红侧沟茧蜂对棉铃虫取食诱导的反枝苋、苘麻的趋性反应，分析了反枝苋、苘麻挥发物的组分，采用EAG测定对寄生蜂具有电生理活性的物质，室内测定了寄生蜂对单个信息物质的行为趋性。田间测定了不同类型挥发物对寄生蜂的吸引性及田间罩笼试验明确了挥发物对寄生蜂寄生棉铃虫的影响。Y型管行为测定发现棉铃虫取食、茉莉酸甲酯MeJA诱导的的反枝苋，棉铃虫取食的苘麻对中红侧沟茧蜂有吸引作用，明确了棉铃虫取食诱导的两种杂草挥发物在中红侧沟茧蜂寻找定位寄主中有重要作用。不同处理杂草（反枝苋、苘麻）分别与对照健康植株比较，挥发物种类和含量均多于对照，从机制上推测棉铃虫天敌中红侧沟茧蜂识别和利用的杂草信号可能是诱导原有挥发物量的增加。室内EAG电生理活性、 Y型管行为测定及室外田间挂板试验明确了反枝苋释放的6-Methyl-5-hepten-2-one， 苘麻中Caryophyllene是中红侧沟茧蜂用于定位寄主的关键化合物。大田罩笼试验证明6-Methyl-5-hepten-2-one和Caryphyllene虽然可以提高中红侧沟茧蜂对棉铃虫幼虫的寄生率，但并不显著。本项目研究首次阐述了害虫取食诱导杂草释放的挥发物在棉铃虫天敌中红侧沟茧蜂寻找和定位寄主中的功能，为研制对寄生蜂有吸引能力的缓释剂奠定基础，为害虫可持续治理提供科学依据。