In natural systems, pre‐adult stages of some insect herbivores are known to be attacked by several species of parasitoids. Under certain conditions, hosts may be simultaneously parasitized by more than one parasitoid species (= multiparasitism), even though only one parasitoid species can successfully develop in an individual host. Here, we compared development, survival, and intrinsic competitive interactions among three species of solitary larval endoparasitoids, Campoletis sonorensis (Cameron) (Hymenoptera: Ichneumonidae), Microplitis demolitor Wilkinson, and Microplitis croceipes (Cresson) (Hymenoptera: Braconidae), in singly parasitized and multiparasitized hosts. The three species differed in certain traits, such as in host usage strategies and adult body size. Campoletis sonorensis and M. demolitor survived equally well to eclosion in two host species that differed profoundly in size, Pseudoplusia includens (Walker) and the larger Heliothis virescens (Fabricius) (both Lepidoptera: Noctuidae). Egg‐to‐adult development time in C. sonorensis and M. demolitor also differed in the two hosts. Moreover, adult body mass in C. sonorensis (and not M. demolitor) was greater when developing in H. virescens larvae. We then monitored the outcome of competitive interactions in host larvae that were parasitized by one parasitoid species and subsequently multiparasitized by another species at various time intervals (0, 6, 24, and 48 h) after the initial parasitism. These experiments revealed that M. croceipes was generally a superior competitor to the other two species, whereas M. demolitor was the poorest competitor, with C. sonorensis being intermediate in this capacity. However, competition sometimes incurred fitness costs in M. croceipes and C. sonorensis, with longer development time and/or smaller adult mass observed in surviving wasps emerging from multiparasitized hosts. Our results suggest that rapid growth and large size relative to competitors of a similar age may be beneficial in aggressive intrinsic competition.

中文翻译：

---

三种内寄生蜂的内在竞争及其对生存和发育的影响

在自然系统中，已知一些昆虫食草动物的成年前阶段会受到几种寄生蜂的攻击。在某些条件下，宿主可能同时被一种以上的寄生物种寄生（= 多寄生），即使只有一种寄生物种可以在单个宿主中成功发育。在这里，我们比较了三种孤立的内寄生幼虫幼虫的发育、存活和内在竞争相互作用，Campoletis sonorensis（Cameron）（膜翅目：Ichneumonidae），Microplitis demolkinson 和 Microplitis croceipes（Cresson）（膜翅目：Braconidae），在寄生蜂中和多寄生宿主。这三个物种在某些特征上有所不同，例如宿主使用策略和成年体型。Campoletis sonorensis 和 M. 在大小差异很大的两种寄主物种中，爆破者同样很好地存活下来，包括 Pseudoplusia includens (Walker) 和较大的 Heliothis virescens (Fabricius)（均为鳞翅目：夜蛾科）。C. sonorensis 和 M. demolitor 的卵到成虫发育时间在两个宿主中也不同。此外，在 H. virescens 幼虫中发育时，C. sonorensis（而不是 M. demolitor）的成年体重更大。然后，我们在初始寄生后的不同时间间隔（0、6、24 和 48 小时）监测了被一种寄生物种寄生并随后被另一种物种多寄生的寄主幼虫的竞争性相互作用的结果。这些实验表明，M. croceipes 通常是其他两个物种的优越竞争者，而 M. demolitor 是最差的竞争者，C. 在这方面，sonorensis 处于中间位置。然而，竞争有时会导致 M.croceipes 和 C.sonorensis 的健康成本，在从多寄生宿主中出现的幸存黄蜂中观察到更长的发育时间和/或较小的成年质量。我们的结果表明，相对于类似年龄的竞争对手而言，快速增长和大规模可能有利于激进的内在竞争。