斜纹夜蛾触角叶神经元及其对植物气味和性信息素的反应

Antennal lobe neurons of Spodoptera litura( Lepidoptera: Noctuidae) and their responses to plant odors and sex pheromones

【目的】探索斜纹夜蛾Spodoptera litura触角叶结构及其神经元对植物气味和性信息素的神经识别机制。【方法】利用共聚焦激光技术扫描斜纹夜蛾成虫触角叶结构,同时采用多通道电生理技术(multi-unit recording,MR)记录斜纹夜蛾触角叶对6种寄主植物气味化合物(苯甲醛、苯甲醇、苯乙醛、水杨醛、乙酸叶醇酯和己烯醛)及性信息素顺9反11十四碳二烯乙酸酯和顺9反12十四碳二烯乙酸酯的反应;并在风洞中测定分析斜纹夜蛾对上述化合物的定向行为反应。【结果】共聚焦激光扫描结果显示,雄性和雌性斜纹夜蛾触角叶内分别密集地分布有67和66个神经纤维球;而雌性斜纹夜蛾触角叶内的纤维球总体积和平均体积都高于雄性。负责识别和追踪性信息素的扩大型纤维球复合体(macroglomerular complex,MGC)只在雄性斜纹夜蛾触角叶内发现。MR试验结果显示斜纹夜蛾触角叶内神经元具有3种自发放电模式:稀疏放电(不规则的放电频率)、温和放电(宽而慢的放电频率)和密集放电(暴发性的放电频率)。同时,斜纹夜蛾触角叶神经元对所有刺激的气味表现出3种反应类型:兴奋性、抑制性和无反应。神经元对气味的兴奋性和抑制性反应以及无反应取决于刺激化合物的结构和浓度。雌虫的触角叶神经元对性信息素和单一的植物气味表现出很小的反应,而雄虫对两种性信息素以及苯甲醛、苯甲醇、苯乙醛和水杨醛具有很强的兴奋性反应。斜纹夜蛾风洞试验也显示绝大部分的斜纹夜蛾雄虫都选择停留在性信息素和芳香族化合物上,这与MR的结果一致。【结论】神经元的反应强度和刺激化合物浓度之间的关系根据不同的神经元和刺激化合物而有所不同。在测试的浓度范围内,雄虫触角叶神经元对性信息素的反应强度随着浓度的增加而加强,但是除乙酸叶醇酯外,对其他植物气味的反应强度在测试的浓度范围内没有显著的变化。

【Aim】This study aims to understand the structure of the antennal lobe（ AL） of the tobacco cutworm,Spodoptera litura and its neuronal activities in response to plant volatiles and sex pheromones.【Methods】The structure of the antennal lobe of S. litura adults was scanned and observed by using the confocal laser scanning. The neuronal activities of AL were recorded and analyzed through multi-unit recording（ MR） method when the antennae were stimulated by six plant-derived volatile compounds including benzaldehyde,benzyl alcohol,phenylacetaldehyde（ PAA）,2-hydroxybenzaldehyde,cis-3-hexenyl acetate, and trans-2-hexenal, and sex pheromones including（ Z,E）-9,11-tetradecadienyl acetate（ Z9E11-14： Ac） and（ Z,E）-9,12-tetradecadienyl acetate（ Z9E12-14： Ac）,respectively. Wind tunnel was employed as the bioassay tool to test the behavioral responses of S. litura adults to the stimulants in order to confirm the neuronal activities shown in the MR experiments. 【Results】The ALs in the brain of S. litura adults identified in the confocal laser scanning were composed of 67 and 66 glomeruli in males and females, respectively. As reported in previous studies, a macroglomerular complex（ MGC） dealing with pheromone information,was only found in the AL of male adults. The total and average volumes of glomeruli in female adults were higher than those in male adults. The MR resultsshowed three spontaneous discharge patterns of neurons,i. e.,diffuse spiking（ irregular frequency）,moderate spiking（ slower and broader distributional frequency）, and fast spiking（ bursting high frequency）. Three types of neuron responses to odor stimulation were present in all recordings,i. e.,excitatory,inhibitory,and unresponsive. The response types（ excitatory,inhibitory or no response） in the AL neurons were found to be dependent on the chemical structure of stimulants and their concentrations. The AL neurons of female adults had weak response to sex pheromones and single component of the tested plant volatiles,while those of male adults showed strong excitatory responses to sex pheromones Z9E11-14： Ac and Z9E12-14： Ac,benzaldehyde,benzyl alcohol,and PAA,suggesting the effect of aromatic compounds. The wind tunnel tests indicated that the majority of male adults significantly chose to stay on sex pheromones and aromatic compounds,and this was consistent with the MR results. 【Conclusion】The relationship between the neuronal responses of female adults of S. litura and the concentrations of all stimuli is different,depending on different neurons or stimulus chemicals.The neuronal activities of male adults are positively correlated to the concentrations of sex pheromones within the tested range,but show no significant differences among the tested concentrations of the plant odors except for cis-3-hexenyl acetate.