Cost of parasite exposure depends on host ontogeny

Fear comes at a cost, and exposure to parasites can elicit non-consumptive
effects (NCEs in hosts that come at such a cost. While NCEs are well
documented, the influence of host developmental stage on these effects
remains poorly understood. Using Drosophila nigrospiracula and its
ectoparasite Macrocheles subbadius, we tested whether early-life exposure
(egg and pupal stages) to mites altered host development and survival.
First, we exposed eggs to direct and indirect mite cues to assess effects
on larval emergence. We then conducted two follow-up experiments to
evaluate microbial transfer from mites and feeding behaviour. Next, we
exposed pupae at two distinct developmental stages and recorded both
emergence success and mite longevity. Mites were highly effective at
consuming fly eggs, but pupae were resistant to direct parasitism. No NCEs
were observed from indirect egg exposure; however, host developmental
state significantly influences pupal NCEs. Less developed pupae had
reduced emergence when exposed to mites, compared to more developed pupae
that had detached from the puparium wall. These results indicate that the
cost of parasite exposure is developmentally dependent, and that
metamorphosis plays a critical role in shaping host susceptibility to
non-consumptive parasite effects.