State-dependent host acceptance in the parasitoid Copidosoma koehleri: the effect of intervals between host encounters

Abstract

Choosing suitable hosts is an important component of parasitoid fitness. Many parasitoids reject already-parasitized hosts. In some species, females reject hosts in which they had recently oviposited, but accept these hosts minutes or hours later. Parasitoids were suggested to mark hosts with repellent pheromones at oviposition and to accept them again after the mark fades. We tested a complementary hypothesis, stating that parasitoids’ host acceptance thresholds decrease with time since their previous oviposition because of a change in internal state, independent of the hosts’ deterrent marking. We scored the acceptance of hosts (eggs of the moth Phthorimaea operculella, Gelechiidae) by Copidosoma koehleri (Encyrtidae) parasitoids in single-choice experiments. Acceptance of self-parasitized (low-quality) hosts increased with time since the wasps’ previous host encounter. The wasps accepted two non-parasitized (high-quality) hosts within a 5-s presentation interval, indicating that they are physiologically able to oviposit twice in quick succession. Parasitized hosts, presented after varying time intervals to conspecifics with uniform host encounter experience, were accepted at similar frequencies. However, as predicted by the working hypothesis, increasing the time elapsed since the wasps’ last oviposition significantly enhanced the acceptance rates of hosts that had been parasitized by conspecifics 2 min earlier. Learning of host-associated cues during oviposition may enable wasps to identify and reject parasitized hosts, while fading of this association from their short-term memory during periods with no host encounters could trigger acceptance of parasitized hosts. State-dependent host acceptance may adaptively allow wasps to avoid self-superparasitism and to adjust conspecific superparasitism rates to foraging conditions.