Effects of the Stress of Beauveria bassiana on the Reproductive Success of an Idiobiont Parasitoid, Sclerodermus guani

In the complex interplay among parasitic wasps, their insect hosts, and pathogenic microbes, the system involving <i>Sclerodermus guani</i> (Hymenoptera: Bethylidae) (a parasitoid wasp), <i>Monochamus alternatus</i> (Coleoptera: Cerambycidae) (the pine sawyer beetle, its host), and <i>Beauveria bassiana</i> (Hypocreales: Cordycipitaceae) (a fungus) presents a unique scenario where wasp offspring develop within a nearly sealed host gallery. This nursery is vulnerable to fungal invasion, often introduced by the foraging female wasps or <i>M. alternatus</i> itself, creating a three-way interaction where the fungus can infect both <i>M. alternatus</i> and <i>S. guani</i>. To assess how the route and timing of fungal exposure impact the <i>S. guani</i> population, we simulated this system by introducing different concentrations of <i>B. bassiana</i> either directly to the female wasps or to <i>M. alternatus</i> prior to parasitism. We further examined the effect of exposure timing by applying the fungus at different developmental stages of the <i>S. guani</i> offspring. Key population parameters, including the reproductive capacity of female wasps, the survival and developmental fitness of <i>S. guani</i> offspring and the germination period of hyphae, were measured. The results indicated that the most severe damage to populations of <i>S. guani</i> occurs when its host, <i>M. alternatus</i>, is infected by <i>B. bassiana</i>. Among the various developmental stages, <i>S. guani</i> offspring exhibited the greatest vulnerability during mid-to-late larval stages, whereas the egg and pupa within cocoon stages demonstrated a higher tolerance. We conclude that both the pathway and the timing of fungal exposure are critical factors influencing its impact. These findings provide valuable insights for optimizing the integrated use of biological agents in pest management, informing strategies that mitigate adverse effects on beneficial parasitoid wasps.