Parasitoid-induced host egg abortion: An underappreciated component of biological control services provided by egg parasitoids

• Parasitoids often kill their hosts without successfully reproducing.
• We focus on host egg abortion caused by egg parasitoids.
• Two case studies are presented to illustrate the importance of studying host egg abortion.
• Host egg abortion by parasitoids has wide-ranging implications for biological control.

Accurate evaluation of the biological control services provided by insect natural enemies requires a consideration of the full diversity of means by which they can cause reductions in host or prey populations. Here, we discuss the fact that host attacks by egg parasitoids often result in failed parasitoid offspring development, while causing the host egg to abort. This parasitoid-induced host egg abortion is rarely considered explicitly, resulting in underestimations of the impact of these important biological control agents on populations of both target and non-target hosts. Two case studies are presented to illustrate the prevalence and implications of parasitoid-induced host egg abortion. The first presents a multi-species/strain dataset from the Trichogrammatidae, while considering the additional importance of host species for egg abortion rates. The second case study focuses on indigenous parasitoid attack on the brown marmorated stink bug, Halyomorpha halys Stål (Hemiptera: Pentatomidae), suggesting that the degree of shared evolutionary history between parasitoids and their hosts is an important determinant of the amount of host egg abortion, that there is inter-individual variation among parasitoids of the same species for the capacity to abort host eggs, and that abortion capacity is potentially a desirable trait that could be subjected to artificial selection. We argue that parasitoid-induced host egg abortion and related forms of non-reproductive parasitoid-induced mortality could have important implications for the modeling of host-parasitoid population dynamics, the assessment of indigenous parasitoid impact following biological invasions, and host range testing of parasitoids as part of classical biological control programmes.