非传粉小蜂的食性及其对榕树-传粉小蜂系统稳定性的影响

Diet of Non-pollinating Wasps and Their Impact on the Stability of Fig-pollinator Wasp Mutualism

榕树与其传粉小蜂形成了高度专一的互惠共生系统。非传粉小蜂则是该系统的资源掠夺者,但它与该系统共存的机制仍不清楚。于2003年12月—2004年4月在西双版纳以聚果榕(FicusracemosaL.)为材料,研究了寄生在聚果榕榕果内的5种非传粉小蜂的食性及相互关系,以探讨非传粉小蜂与榕树-传粉小蜂系统共存的机制。结果表明:寄生在聚果榕榕果内的5种非传粉小蜂中,仅PlatyneuratestaceaMotschulsky和PlatyneuramayriRasplus能刺激子房发育成瘿花,是造瘿者;Apocryptasp.,ApocryptawestwoodiGrandi和PlatyneuraagraensisJoseph不能刺激子房发育成瘿花,是拟寄生者。传粉小蜂的拟寄生者和造瘿者对传粉小蜂有负的影响,但在蚂蚁和造瘿者的拟寄生蜂作用下,这种负面影响并不显著,而且它们对榕树繁殖没有显著影响。对小蜂自然种群的分析表明,传粉小蜂处于优势地位。说明在自然情况下传粉小蜂的拟寄生者和造瘿者的种群维持在一个较低水平,对榕树-传粉小蜂系统稳定性影响较小,故能与之长期共存。

Ficus （Moraceae） and their species-specific pollinator wasps （Agaonidae） form a remarkable plant-insect obligate mutualism, and non-pollinators are the exploiters of the mutualism. The negative impact of exploiters on the reciprocal mutualists might disrupt the reciprocal mutualism in the process of evolution, but how the exploiters could coexist with the reciprocal mutualsits is not still clear. In this study, the diet of the five species of non-pollinators and relationship among fig wasps were analyzed on Ficus racemosa L. in Xishuangbanna from Dec. 2003 to Apr. 2004. In a controlled experiment pollinators and each species of non-pollinators oviposited and counts of wasps and seeds in mature figs were conducted. The results indicated that only Platyneura testacea Motschulsky and Platyneura mayri Rasplus are gallmakers, which can induce the ovaries into galls; Apocrypta sp., Apocrypta westwoodi Grandi and Platyneura agraensis Joseph are the parasitoids. The gall-makers and the parasitoids of pollinators have negative impacts on pollinators, but the impacts are not significant because of the influence of the ants and parasitoids of gall-makers. Additionally, the experiment excluding non-pollinators oviposition showed that the number of offspring of pollinators and seeds were not significantly different with the natural fruits. Moreover, the analysis on the natural population structure of fig wasps revealed that the pollinators are the dominant species. So in the natural condition, the abundance of gall-makers and parasitoids of pollinators are below the level needed to exclude pollinators, and thus they have a relatively weak impact on the stability of fig-pollinator mutualism and can coexist with the mutualism.