In solitary endoparasitoids, oviposition in a host previously parasitized by a conspecific (superparasitism) leads to intraspecific competition, resulting in the elimination of all but one parasitoid offspring. Therefore, avoidance of parasitized hosts presents a strong selective advantage for such parasitoid species. Parasitoids use herbivore-induced plant volatiles (HIPVs) to find their hosts. In this study, we evaluated the ability of Microplitis croceipes (Hymenoptera: Braconidae) to discriminate between unparasitized and parasitized Heliothis virescens (Lepidoptera: Noctuidae) larvae using cotton plant odors as cues. A combination of behavioral and analytical techniques were used to test two hypotheses: (i) parasitoids will show preference for plant odors induced by unparasitized hosts over odors induced by parasitized hosts, and (ii) the parasitism status of herbivores affects HIPV emission in plants. Heliothis virescens larvae were parasitized for varying durations (0, 2 and 6-days after parasitism (DAP)). In four-choice olfactometer bioassays, female M. croceipes showed greater attraction to plant odors induced by unparasitized hosts compared to plant odors induced by parasitized hosts (2 and 6-DAP). Comparative gas chromatography-mass spectrometry analyses of cotton volatiles indicated reduced emission of 10 out of 21 identified compounds from plants infested by parasitized hosts compared with plants infested by unparasitized hosts. The results suggest that changes in plant volatile emission due to the parasitism status of infesting herbivores affect recruitment of parasitoids. Avoidance of superparasitism using plant odors optimizes host foraging in M. croceipes, and this strategy may be widespread in solitary parasitoid species.

在孤立的类内寄生虫中，先前被同种（超寄生）寄生的宿主的产卵会导致种内竞争，从而导致除一个寄生虫后代之外的所有子代都消失了。因此，避免寄生的宿主为这种寄生的物种提供了强大的选择性优势。寄生虫利用草食动物诱导的植物挥发物（HIPV）来寻找它们的宿主。在这项研究中，我们评估的能力茧croceipes（膜翅目：茧蜂科）到未被寄生区分和寄生夜蛾（鳞翅目：夜蛾科）幼虫，以棉株气味为线索。行为和分析技术的结合被用来检验两个假设：（i）寄生虫比未寄生虫的宿主表现出比未寄生虫的宿主更诱人的植物气味;（ii）草食动物的寄生状态影响植物中HIPV的排放。寄生了Heliosthis virescens的幼虫，持续了不同的时间（寄生后0、2和6天（DAP））。四选择区嗅觉生物测定，女性中号。番红花与未寄生虫宿主诱导的植物气味（2和6-DAP）相比，对非寄生虫宿主诱导的植物气味具有更大的吸引力。棉挥发物的比较气相色谱-质谱分析表明，与未寄生虫宿主侵染的植物相比，从被寄生虫宿主侵染的植物中鉴定出的21种化合物中，有10种的排放减少。结果表明，由于侵扰性草食动物的寄生状态引起的植物挥发物排放的变化会影响寄生虫的募集。利用植物气味避免超寄生虫可以优化番红花螺的宿主觅食，并且这种策略可能在单独的寄生寄生虫物种中得到广泛应用。