挥发性信息化合物与学习行为在平腹小蜂寄主选择过程中的作用

Roles of volatile infochemicals and learning behavior in the host selection process of Anastatus japonicus

利用Tenax-TA吸附剂法结合气相色谱和气质联用仪,在荔枝叶片中分离鉴定了26种挥发性物质,包括萜类、醇类、醛类、酯类和吲哚等不同种类的化合物,其主要成分为萜烯类物质。利用固相微萃取仪(SPME)结合气相色谱的方法,从荔枝蝽挥发物中分离得到了5种以上的化合物,(E)-2-己烯醛为主要成分之一。采用"Y"型嗅觉仪进行的行为分析表明,由柞蚕卵饲养的平腹小蜂对荔枝叶片(第一营养级)和寄主卵(第二营养级)的挥发物无明显趋性,而荔枝蝽成虫挥发物对平腹小蜂有显著的吸引作用。进一步的研究表明,学习行为在平腹小蜂寄主选择行为中有重要作用,无学习经历的平腹小蜂对荔枝叶片挥发物及其主要成分子丁香烯无明显趋性,但经过学习经历以后,选择荔枝叶片挥发物以及子丁香烯的平腹小蜂的数量显著多于空白对照。然而,不论有无学习经历,选择荔枝蝽成虫主要挥发物(E)-2-己烯醛的平腹小蜂的数量都明显高于选择空白对照的数量。

Volatile infochemicals play an important role in the location of hosts by parasitoids.There are several potential sources of infochemicals employed by parasitoids:the host plant,the parasitoid itself,other organisms associated with the host,or chemicals released as a result of interactions between the parasitoid and host plant.We used a model system consisting of the tree Lichi chinensis, the adult insect Tessaratoma papillosa and its egg parasitoid Anastatus japonicus to investigate the role of volatile infochemicals from different potential sources and the change in behavior of parastoid in locating the host with repeated exposure.Volatiles from Lichi leaves were collected from headspace using a TenaxTA trap and analyzed by GC and GCMS.Twentysix compounds were identified, including terpenoids,alcohols,ketones,aldehyde,acetate,indole and 4 unknown compounds.Terpenoids were the main components,and the major components of which were βcaryophyllene and αhumulene.Five volatiles were collected with a SPME from the adult T.papillosa. Analysis by GC indicated(E)2hexenal was the main component.No volatile chemicals could be collected from T.papillosa eggs using either a TenaxTA trap or SPME.A Ytube olfactometer was used to study the behavioral responses of adult parasitoid A.japonicus to volatiles from different sources.Inexperienced naive wasps were more attracted to adult T.papillosa after exposure to their volatiles compared to lichi leaves,T.papillosa eggs or clean air.Learning behavior for different sources of volatiles by wasps was examined using synthetic chemicals in a Ytube olfactometer.Inexperienced naive wasps showed no preference to the blend of lichi leaves volatiles or one of its main components,βcaryophyllene.However,responses of the wasp to the plant volatiles or βcaryophyllene were significantly enhanced after initial exposure to these volatiles and host eggs simultaneously.(E)2hexenal,one of the main components of volatiles from adult T.papillosa,elicited a significant response in inexperienced naive wasps,but did not enhance the response after conditioning.Hence,the parasitoid A.japonicus females can learn to associate host eggs with plant volatiles and then using these volatiles and/or using volatiles from adult T.papillosa as chemical cues in their host location process.