外寄生性花绒寄甲的寄生选择及其发育表现

Parasitization preference and developmental performances in the ectoparasitoid Dastarcus helophoroides( Coleoptera: Bothrideridae)

"选择-表现"假说认为,成虫应该选择有利于子代发育的高品质寄主,但在寄主选择中,除了寄主品质外,其他因素也可能影响寄主选择决策。寄主选择研究通常以成虫为对象,而对那些初龄幼虫选择寄主的寄生性昆虫很少关注。以1龄幼虫积极搜寻寄主的寄生性花绒寄甲为模式生物,采用双选试验设计,观察了花绒寄甲初孵幼虫在不同体重青杨天牛幼虫之间、在已被寄生与健康的黄粉虫蛹之间的寄生选择性;然后采用回归设计,观察了花绒寄甲寄生若干不同体重的青杨天牛幼虫后的发育表现。研究结果表明,花绒寄甲1龄幼虫对体型较大的青杨天牛幼虫的选择偏好显著大于对体型较小的寄主幼虫的选择,选择大体型幼虫的比值比是选择小体型幼虫的4.55倍;对已被寄生的寄主黄粉虫蛹的选择偏好显著大于对健康寄主蛹的选择,选择已被寄生寄主的比值比是选择健康寄主的12.57倍。寄生青杨天牛幼虫的花绒寄甲幼虫发育历期平均为11.49 d、蛹历期为26.67 d、幼虫发育至成虫的羽化率>50%,这些发育表现与寄生时青杨天牛幼虫的体重没有显著关系。但刚羽化寄甲成虫体重与寄生时寄主的体重存在显著的正直线关系:寄生时的寄主体重每增大0.01 g,羽化出的寄甲成虫体重增大近0.08%;方差分析寄甲成虫体重在不同寄主体重水平之间的差异表明,从体型较大寄主中羽化的寄甲成虫体重显著大于从体型较小寄主中羽化的成虫。研究结果说明,花绒寄甲初孵幼虫在寄主选择决策时,在寄主体型大小与被寄生状态之间可能采取折衷对策,而且对体型大小不同的寄主选择与子代发育适合度表现存在一致性,从而支持"选择-表现"假说。

The preference-performance hypothesis predicts that adults should select high quality hosts which can provide offspring with good resources for development. Other factors,however,can also influence the parasitoids in making decisions on the choice. Previus such studies often use adult parasitoids as model systems,but give scant attention to insects in which host search and selection are made by neonate larvae. Here we used as the model system the ectoparasitic beetle Dastarcus helophoroides,which depends its neonate larvae to search and select hosts. We first,using the long-horned beetle Saperda populnea larvae and the flour beetle Tenebrio molitor pupae as hosts,investigated whether D. helophoroides first instar larvae showed parasitization preferences between hosts varying in body size or in parasitism by conspecifics. We then,using the experimental regression design, examined developmental performances in relation to host body weight atparasitism. D. helophoroides first instar larva showed a significant preference for larger sized S. populnea larva,which were4.55 times as likely to be parasitized as the smaller sized larva. D. helophoroides first instar larva preferred the parasitized T. molitor pupa over the healthy for parasitization,12.57 times as likely for the parasitized as for the healthy host pupae. D.helophoroides larval development time（ averaged to 11.49 d）,pupal duration（ 26.67 d）,and larva-to-adult survival rate（ 50%） were not related with host body weight at parasitism. But adult body weight at emergence significantly increased linearly with host body weight at parasitism,by an increase of almost 0. 08% with each 0. 01 g increment in host body weight. ANOVA and multiple comparison tests showed that D. helophoroides adult at emergence was significantly larger in body weight from attacking larger than smaller sized hosts. The results of our study resuggest that D. helophoroides first instar larva may take a trade-off between host body size and parasitism in making decisions on parasitization. In addition,our results suggest that the prefernece for larger hosts in body size by D. helophoroides first instar larva is aligned with developmental performances of offpring,lending suport for the preference-performance hypothesis.