Consequences of infanticide for a gregarious ectoparasitoid of leafroller larvae

1. In this laboratory study, the clutch size and handling time of Goniozus jacintae were investigated, a comparison of its life‐history performance between primary and secondary (laid after infanticide events) broods was carried out, and the lipid and protein concentrations in the haemolymph of non‐parasitised and parasitised hosts were estimated. 2. It was found that G. jacintae temporarily paralysed its host larvae for 66 min and briefly guarded its brood for 66 min. The clutch size of G. jacintae increased from two to seven with increasing larval fresh weight of its host, and both ovicide and larvicide of primary clutches occurred in 81% of encounters. 3. Secondary clutches of G. jacintae were significantly larger than primary clutches in two of three ovicide treatments for the same host individuals. Secondary clutches also experienced greater brood survivorship than primary clutches. 4. Lipid concentrations were consistently higher in the haemolymph of parasitised hosts, and protein concentrations were initially higher (until egg hatch), but increased at a lower rate in parasitised hosts than in non‐parasitised hosts. 5. This study is the first to provide evidence that improved nutritional quality could be an important benefit of infanticide for an insect parasitoid, allowing for larger clutch size and improved brood survivorship among secondary broods.