Reproductive trade-offs in the click beetle, Agriotes obscurus, exposed to the fungal pathogen Metarhizium brunneum

Several of the more pathogenic fungal species that infect insects have been developed as biological control agents. Adult insects can respond to potentially lifespan-reducing pathogen challenges by fighting infection, allocating resources to resistance over other activities. Alternatively, they can allocate resources to maximizing fecundity in response to early death, the terminal investment hypothesis. The click beetle Agriotes obscurus is an agricultural pest, and the fungus Metarhizium brunneum is being developed as a control agent. I examined the impact of M. brunneum challenge on A. obscurus reproduction and whether this changed under different nutritional conditions in beetles of varying ages. Beetles reduced their preoviposition period in response to fungal-induced decreases in lifespan when they were older, resulting in maintained fecundity, or under starved conditions, although fecundity could not reach the level of fed beetles. These results suggest that M. brunneum should be used early in the season when resources are abundant.