Egg-laying decisions by female insects should balance aspects related to immature survival and foraging profitability of emerging larvae. Using field-captured individuals, we characterized the egg distribution of Istocheta aldrichi (Diptera: Tachinidae) on the body of its adult host, the Japanese beetle Popillia japonica (Coleoptera: Scarabaeidae). We determined whether the pattern varies as a function of host sex and the number of eggs laid on a given host. Out of the 5667 eggs observed, 95.9% were located on the host pronotum. Furthermore, eggs on the pronotum were mostly positioned in the center of this sclerite and oriented perpendicular to the host body axis. The proportion of eggs placed on other parts of the host body increased with the number of eggs per host (superparasitism). Successful development of I. aldrichi into pupae was maximum for eggs laid on the host pronotum than for eggs laid on other parts of the host. Oviposition decisions in I. aldrichi are likely shaped by trade-offs between vulnerability to grooming by the host and foraging profitability of neonate larvae (i.e., their capacity to penetrate the host cuticle), but also by the mating and defensive behaviors of the Japanese beetle.

雌性昆虫的产卵决定应平衡与新生幼虫的未成熟生存和觅食盈利能力相关的方面。利用野外捕获的个体，我们描述了Istocheta aldrichi （双翅目：Tachinidae）的卵在其成虫宿主日本甲虫Popillia japonica（鞘翅目：Scarabaeidae）身体上的分布。我们确定了这种模式是否随宿主性别和给定宿主产卵数量的变化而变化。在观察到的 5667 个卵中，95.9% 位于宿主前胸背板上。此外，前胸背板上的卵大多位于该骨片的中心，并垂直于宿主身体轴线。卵放置在宿主身体其他部位的比例随着每个宿主的卵数量的增加而增加（超寄生）。产在寄主前胸背板上的卵比产在寄主其他部位的卵能最大程度地成功发育成蛹。I. aldrichi的产卵决定可能是由宿主易受修饰的脆弱性和新生幼虫的觅食盈利能力（即它们穿透宿主角质层的能力）之间的权衡决定的，但也受日本甲虫的交配和防御行为的影响。