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Superparasitism is a widespread phenomenon. Having accepted superparasitism, mated female parasitoids must decide on the sex of each egg they subsequently lay into the same host. Theory predicts that this decision is either based on host quality, when more male eggs are laid in hosts that are already parasitized because they are perceived to be of poorer quality; or more eggs are laid of the sex that is most likely to be a strong larval competitor, i.e. generally females. Anastatus disparis is a facultative endoparasitic egg parasitoid. We used ‘artificial’ hosts to explore outcomes of decision making by A. disparis during superparasitism under a manipulated absence of larval competition. When only one egg was laid it was always female. As the number of eggs laid increased, so more of them were male. This supports the theory that oviposition decisions are based on host quality; more male eggs were laid in hosts that were already parasitized and thus of poorer quality. In a second experiment, eggs were exposed to parasitoids for different periods of time. Half the eggs were dissected to determine the number of parasitoid eggs that had been laid. The remaining eggs were incubated and the number and sex of offspring that ultimately emerged, following larval competition, were recorded. Under superparasitism conditions fierce larval competition ensued; only one offspring survived and they were predominantly female. In conclusion, oviposition decisions by female A. disparis accepting self-superparasitism were made based on host quality.

In China Aromia bungii (Coleoptera: Cerambycidae) is an economically important wood-boring pest of Prunus trees, particularly peach, and it has recently entered Japan and several other countries as an invasive species. Larvae of A. bungii are attacked by parasitoid species in the genus Sclerodermus (Hymenoptera: Bethylidae), which have potential to be released as biological control agents. In this study we evaluated the olfactory responses and parasitism rates of three Sclerodermus species against A. bungii when reared on the substitute host, Tenebrio molitor (Coleoptera: Tenebrionidae). In Y-tube olfactometer studies, the odor of frass from the larvae of A. bungii was highly attractive to S. guani adults, but not to S. sichuanensis or S. pupariae adults. When reared on A. bungii larvae (rather than T. molitor) for one generation, S. sichuanensis adults were also attracted to the odor of frass from A. bungii larvae. This indicates that learning plays an important and positive role in successful host location by S. sichuanensis. For S. pupariae, it is possible that more extensive learning experience is required to adapt to A. bungii larvae. When we studied mortality of immature A. bungii larvae in infested peach tree logs under semi-field conditions, we found that mortality rates were similar for the three species of Sclerodermus: S. guani 54.81 ± 8.07%, S. sichuanensis 42.59 ± 9.01% and S. pupariae 40 ± 6.76%, respectively. However, there was a significant difference in mortality between S. guani and the control. Parasitism rates caused by S. sichuanensis (35.56 ± 9.48%) were similar to S. guani (42.96 ± 14.20%) and S. pupariae (34.44 ± 10.10%). From these results we suggest that S. guani would be the best candidate for biological control of the immature stages of A. bungii, and that more field trials should be done in the future.