Host selection is not expressed for underground hosts in a pupal parasitoid

Host–parasitoid dynamics is critically influenced by variability in parasitism risk among hosts, and the host preference of the parasitoid is one of the factors causing such variability. This study examined the host preferences of the pupal parasitoid Dirhinus giffardii (Silvestri) (Hymenoptera: Chalcididae) on pupae of the oriental fruit fly Bactrocera dorsalis (Hendel) (Diptera: Tephritidae) in the laboratory. Dirhinus giffardii prefers large hosts and avoids hosts nearing eclosion when hosts are exposed to the parasitoid. This study reexamined the preferences when host pupae are in the soil (simulated by peat moss) because tephritid hosts, including B. dorsalis, pupate in the soil. Results showed that D. giffardii preferentially parasitized large hosts when hosts were exposed, but host size‐dependent parasitism was absent when hosts were in the soil. Preference on host age was absent even when hosts were exposed, contradicting the results of previous studies. The discrepancy was examined by performing a follow‐up experiment to test the hypothesis that D. giffardii cannot distinguish host age, but eggs that are laid on older hosts cannot develop successfully. The parasitoid successfully hatched regardless of host age, and the hypothesis was rejected. Potential explanations for the discrepancy are discussed. This study shows that a previously known size‐based host preference of the pupal parasitoid Dirhinus giffardii (Hymenoptera: Chalcididae) is expressed only when hosts (oriental fruit fly) are directly exposed on the soil surface but is absent when hosts are in their natural habitat (i.e., in the soil). The study also shows that experimental methods on how parasitism is quantified (i.e., how to determine whether or not a pupal host is actually parasitized) can strongly bias conclusions of host preference studies.