Presence of a conspecific increases superparasitism but not infanticide under self‐ and conspecific superparasitism in a semisolitary parasitoid, Echthrodelphax fairchildii (Hymenoptera: Dryinidae)

Female parasitoids are expected to avoid superparasitism (ovipositing in and/or on parasitized hosts) when unparasitized hosts are available. However, when the supply of unparasitized hosts is restricted, they are expected to self- as well as conspecifically superparasitize. One of the cues of a reduced availability of unparasitized hosts is the presence of a conspecific. Moreover, if the focal species can perform infanticide, after encountering a conspecific female, the females are expected to kill eggs existing in and/or on hosts when superparasitizing, because the eggs are more likely to be laid by others. In this study we investigated whether females of an infanticidal semisolitary parasitoid, Echthrodelphax fairchildii, increase their frequencies of superparasitism and infanticide after encountering a conspecific female. Echthrodelphax fairchildii females are capable of discriminating between self- and conspecific superparasitism until up to 0.75 h after the first egg was laid (self-superparasitism frequency < conspecific superparasitism frequency). As expected, the female parasitoids were more likely to perform self- and conspecific superparasitism after they had encountered a conspecific. In particular, the self-superparasitism frequency increased highly within a short period after the first oviposition, so that no difference between the self- and conspecific superparasitism frequencies was found. In contrast, the infanticidal-probing frequency remained extremely low, irrespective of whether or not the female parasitoids had encountered a conspecific. Moreover, when superparasitizing, females usually laid female eggs. Possible causes for the low frequency of infanticidal probing and the female-biased sex ratio are discussed.