Does Diachasmimorpha longicaudata (Hymenoptera: Braconidae) have a preferential instar to parasitize Tephritidae (Diptera)?

ABSTRACT Diachasmimorpha longicaudata (Ashmead, 1905) is a koinobiont parasitoid of Tephritidae larvae, the third instar larvae of which is considered preferential, but it is able to parasitize other larval stages and compete with native parasitoids. This study investigated the preference and parasitism capacity of D. longicaudata in larvae of different instar of Anastrepha fraterculus (Wiedemann, 1830) (AF) and Ceratitis capitata (Wiedemann, 1824) (CC). The experiments were carried out under laboratory conditions, one instar being offered at a time in parasitism units, with the following choices among the hosts: 25 AF larvae and 25 CC larvae (first, second and third instar were evaluated). The other test was a multiple-choice in relation to the instar, for larvae of the same host species, with three parasitism units being offered, with 15 larvae of each instar. The mean number of formed pupae, emerged parasitoids, parasitized pupae, unviable pupae and sex ratio were evaluated. In the first bioassay, the mean number of emerged parasitoids and parasitized pupae in the AF host were significantly higher in treatments with first and second instar larvae. For CC there was no difference between the instars tested. In the second bioassay, the mean value of emerged parasitoids and parasitized pupae, was higher in second and third instar larvae for CC, and for AF was in second instar larvae. The sex ratio was biased for males in all treatments in both bioassays. The results show that D. longicaudata can parasitize and be successful in all available larval instars, being able to compete with parasitoids of any instar.

摘要 长尾全裂茧蜂（Diachasmimorpha longicaudata, Ashmead, 1905）是实蝇科（Tephritidae）幼虫的抑龄型寄生蜂，其偏好寄生3龄幼虫，但亦可寄生其他龄期的幼虫，并可与本地寄生蜂产生种间竞争。本研究旨在探究长尾全裂茧蜂对南美按实蝇（Anastrepha fraterculus, Wiedemann, 1830，简称AF）及地中海实蝇（Ceratitis capitata, Wiedemann, 1824，简称CC）不同龄期幼虫的寄生偏好与寄生能力。实验均在实验室条件下开展：第一组为寄主种类选择实验，每次仅提供单一龄期的幼虫，设置含25头AF幼虫与25头CC幼虫的处理组，分别测试1、2、3龄幼虫；第二组为寄主龄期选择实验，针对同一寄主物种，设置3组寄生单元，每组包含各龄期幼虫各15头。本研究统计了平均羽化蛹数、寄生蜂羽化数、被寄生蛹数、未存活蛹数及性比等指标。在第一组生物测定中，AF寄主组中1龄与2龄幼虫处理组的寄生蜂羽化数与被寄生蛹数均显著更高；而CC寄主组中，不同龄期处理组间无显著差异。在第二组生物测定中，CC寄主组的寄生蜂羽化数与被寄生蛹数在2龄与3龄幼虫组中更高，AF寄主组则在2龄幼虫组中达到峰值。两组生物测定的所有处理组中，性比均偏向雄性。研究结果表明，长尾全裂茧蜂可寄生并成功繁育于所有供试幼虫龄期，且能够与各龄期的本地寄生蜂形成竞争。