Exploring factors influencing the ecological host range of <i>Trissolcus japonicus</i> : foraging strategy and nontarget host use

Evaluation of potential classical biological control agents typically begins with laboratory testing for their fundamental host range. These experiments are intended to evaluate the propensity for nontarget attack but often do so in highly artificial conditions without considering the unique ecology of different agents. Understanding ecological characteristics early in evaluation is important as it can influence the methods or implications of host range tests and natural enemies are being increasingly found in adventive populations before host range testing is complete. We used Trissolcus japonicus, a potential classical biological control agent of the brown marmorated stink bug (Halyomorpha halys) to evaluate the ecological factors influencing nontarget host use of 5 different nontarget species. Female wasps were equally likely to select nontarget hosts when foraging for separated egg masses in cage experiments, contrary to expectations of previous host range tests. However, when hosts were placed close together, wasps selected the target host more often, suggesting T. japonicus does not perceive choices among separated egg masses. In no-choice experiments, we show that parasitoids exhibit polyphenism when developing on different sized hosts with corresponding reductions in egg load. Emergence success was also influenced by humidity for some but not all host species. Nutrient content differed between host species but was not clearly correlated with fitness of T. japonicus on different hosts. Our results suggest that T. japonicus is likely to parasitize nontarget species that share a niche with H. halys with high success in Podisus maculiventris and Chinavia hilaris hosts.