Host egg pigmentation protects developing parasitoids from ultraviolet radiation

Parasites rely on their hosts not only for nutrition and reproduction, but also for protection against natural enemies and adverse climatic conditions. In host-parasite interactions, protective characteristics of both players are important to consider regarding damaging effects of environmental hazards. While ultraviolet radiation (UVR) is pervasive and harmful to organisms in general, its impact on parasite fitness remains understudied. Moreover, studies that do examine the effects of UV exposure on parasitic organisms tend to neglect host traits, which may vary inter- or intra-specifically and thus confer different levels of environmental protection. We examined in the laboratory whether the UV-protective value of host egg pigmentation could also benefit parasitoids, using the egg parasitoid Telenomus podisi and the predatory stink bug Podisus maculiventris. This host species lays eggs of variable pigmentation levels from light to dark grey, an adaptation protecting its own embryos from UVR. We showed that higher levels of host egg pigmentation protect parasitoids subjected to a developmental exposure to UVR, increasing emergence rates by up to 86% and reducing development time by up to 4%. This protective effect of host pigmentation was context-dependent, being less pronounced at low UVR intensity and towards the end of parasitoid development. Parasitoids that emerged from darker-coloured eggs exposed to UVR were of slightly larger size than those developing in light-coloured eggs, but other fitness-related traits (fecundity, longevity, sex ratio) were unaffected. This study provides the first experimental evidence that host pigmentation can increase host suitability for parasitic organisms, and emphasizes the importance of considering trait variation in interacting species when investigating the susceptibility of ecological communities to important abiotic environmental factors.