取食棉花花外蜜对异色瓢虫成虫营养生理及捕食行为的影响

Plant extrafloral nectar (EFN), which is secreted from the extrafloral nectaries, is an aqueous solution of sugars and amino acids and can be induced by herbivore damadge. Several reports suggest that EFN have positive effects on the longevity, fecundity, predation and foraging preferences of pest's natural enemies, but the mechanism is not clear. To evaluate the effects of EFN on other predatory insects, the typical extrafloral nectaries plant, cotton plant Gossypium hirsutum and Harmonia axyridis which is common in cotton plant fields are used as materials in this study, the chemical composition of cotton EFN is analysised with high performance liquid chromatograph (HPLC) and automatic amino acid analyzer. According to the chemical composition of EFN, artificial nectar is mimicked to feed on Harmonia axyridis and the adult longevity, fecundity, predatory capacity and foraging preferences will be observed . HPLC analysis is used to study the haemolymph sugar profile of Harmonia axyridis and Quantitative reverse transcriptase PCR (qRT-PCR) technic is used to ananlysis the key enzymes' gene expression differences in energy metabolism. The nutritional value, effects of stimulating predation and attraction of EFN are analysised and the mechanism of EFN on Harmonia axyridis is discussed. This study is of momentous significance as it will reveal the ecological function of EFN, be helpful to regulate the tritrophic interactions among host plants, herbivores and natural enemies and look for new pathways to manage cotton pest insects.

花外蜜是植物花外蜜腺分泌的糖和氨基酸的混合物，害虫为害诱导其分泌量增加。报道认为花外蜜对蚂蚁等害虫天敌的寿命、生殖及捕食能力和行为能够产生积极影响，但其作用机制还不清楚。为了明确植物花外蜜对其它捕食性天敌昆虫的影响及作用机制，本研究以典型的花外蜜腺植物-棉花和棉田重要的捕食性天敌-异色瓢虫为试验材料，采用高效液相色谱和氨基酸自动分析仪分析棉花花外蜜的组成及含量，根据测定结果人工模拟花外蜜中的糖和氨基酸成分，测定其对异色瓢虫成虫寿命、繁殖、捕食能力以及捕食行为的影响，采用高效液相色谱技术和荧光定量逆转录PCR（qRT-PCR）技术研究棉花花外蜜对异色瓢虫成虫血淋巴糖浓度及能量代谢中关键酶基因的差异表达，探讨花外蜜对异色瓢虫是否具有营养、刺激取食和引诱效应及其作用机制。该项研究的开展，对于揭示植物花外蜜的生态功能，调控植物-害虫-天敌之间的关系，探索新型环境友好型害虫治理途径具有重要意义。

在该项目的资助下，本研究测定了棉花花外蜜中的糖和氨基酸成分，并根据测定结果进行了棉花花外蜜的人工模拟。研究了棉花花外蜜对异色瓢虫成虫的产卵和寿命的影响，明确了棉花花外蜜能显著增加异色瓢虫的产卵量并显著延长成虫寿命。分析了棉花花外蜜对异色瓢虫捕食能力，嗅觉行为和味觉选择行为的影响，明确了棉花花外蜜的存在降低了异色瓢虫对豆蚜的捕食能力，说明异色瓢虫在最适猎物存在下仍取食一定量的植物花外蜜。棉花花外蜜中的蔗糖和果糖对异色瓢虫有较强的吸引作用，同时棉花花外蜜中的氨基酸尤其是必须氨基酸苯丙氨酸对异色瓢虫有较强的引诱作用。异色瓢虫成虫羽化后花外蜜饲喂与饥饿相比，成虫体内总糖的浓度水平显著升高。异色瓢虫成虫体内总糖的水平能够反映其取食量。采用实时荧光定量PCR方法检测了异色瓢虫成虫营养生理及能量代谢中关键酶海藻糖酶、海藻糖合成酶基因的表达情况，结果表明异色瓢虫成虫饱食后饥饿72 h饲喂棉花花外蜜的雌虫和雄虫海藻糖合成酶基因的表达量升高。因此，棉花花花外蜜对异色瓢虫具有营养和引诱作用，在最适猎物缺乏时花外蜜可以为异色瓢虫提供食物补充。饥饿条件下为异色瓢虫提供棉花花外蜜，异色瓢虫体内总糖浓度升高。海藻糖合成酶可能参与了异色瓢虫对棉花花外蜜的生理代谢过程。在本项目资助下，发表论文3篇，培养研究生2名。