LAUSR

Simple Summary This article studies the interaction between two parasites, a parasitoid (Sclerodermus guani) and an entomopathogenic fungus (Beauveria bassiana) on the same host, a longicorn beetle Monochamus alternatus. We focused on the survival and reproduction of the parasitoid’s parent and its offspring fitness under different concentrations of B. bassiana suspension in the laboratory. The results show that S. guani parent females carrying higher concentrations of the pathogen shorten the pre-reproductive time and regulate their own fertility and their offspring’s survival and development. Under the stress of the entomopathogenic fungus B. bassiana, the mortality effect of the parasitoid S. guani to its host M. alternatus was also assessed by the interspecific relationship model, which contained three dimensionless parameters: the ratio vulnerability, dilution ratio, and PR (the ratio of the total number of parasitoids successfully controlling host larvae M. alternatus to the total number of parasite events during parasitism). These findings shed light on the potential interspecific interactions between the two parasites which were able to coexist and communicate with their hosts in ecological contexts (with a high overlap in time and space) and cause interspecific competition and intraguild predation. Abstract Complex interspecific relationships between parasites and their insect hosts involve multiple factors and are affected by their ecological and evolutionary context. A parasitoid Sclerodermus guani (Hymenoptera: Bethylidae) and an entomopathogenic fungus Beauveria bassiana (Hypocreales: Cordycipitaceae) shared the same host in nature, Monochamus alternatus (Coleoptera: Cerambycidae). They often encountered the semi-enclosed microhabitat of the host larvae or pupae. We tested the survival and reproduction of the parasitoid’s parent and its offspring fitness under different concentrations of B. bassiana suspension. The results show that S. guani parent females carrying higher concentrations of the pathogen shorten the pre-reproductive time and regulate their own fertility and their offspring’s survival and development. This minimal model of the interspecific interactions contains three dimensionless parameters, vulnerability (θ), dilution ratio (δ), and PR, which were used to evaluate the mortality effect of the parasitoid S. guani on its host M. alternatus under the stress of the entomopathogenic fungus B. bassiana. We compared the infection and lethal effect of the fungus B. bassiana with different concentrations to the parasitoid S. guani and the host larvae M. alternatus. At higher concentrations of the pathogen, the parasitoid parent females shorten the pre-reproductive time and regulate their own fertility and their offspring’s survival and development. At moderate concentrations of the pathogen, however, the ability of the parasitoid to exploit the host is more flexible and efficient, possibly reflecting the potential interspecific interactions between the two parasites which were able to coexist and communicate with their hosts in ecological contexts (with a high overlap in time and space) and cause interspecific competition and intraguild predation.