Fitness consequences of host switching by Psix saccharicola, a stink bug egg parasitoid in pistachio orchards

To successfully implement augmentative biological control, it is imperative to identify the most efficient host for parasitoid rearing and the impact of host switching on reproduction when multiple hosts are available. This study examined the effect of host switching on parasitoid fitness and reproduction using the wasp Psix saccharicola Mani (Hymenoptera: Scelionidae), a dominant stink bug egg parasitoid in Iranian pistachio orchards, and two common hosts— Acrosternum arabicum Wagner (Hemiptera: Pentatomidae) and Brachynema germari Kolenati (Hemiptera: Pentatomidae). The results indicated that rearing wasps on A. arabicum was more efficient, resulting in a shorter population doubling time, a shorter mean generation time, and higher finite and intrinsic rates of increase compared to rearing on B. germari . While switching the host from A. arabicum to B. germari led to increased population growth parameters for P. saccharicola in the first generation of host switching, switching the host from B. germari to A. arabicum decreased parasitoid fitness and reproduction. However, the effect of host switching largely disappeared in the second generation after host-switch, suggesting that changes in parasitoid fitness due to host switching could be temporary and may revert in subsequent generations. Our study highlights the importance of evaluating the impact of host switching when implementing a rearing program for P. saccharicola , ultimately leading to more sustainable pest control of stink bugs in pistachio orchards.