Increased susceptibility of Colorado potato beetle to pathogens following exposure to predators

Phytophagous insects must overcome stressful biotic and abiotic conditions throughout their development. Mounting evidence suggests that stress during one life stage can affect mortality in a later developmental stage. For example, we have found that Colorado potato beetle (CPB) larvae exposed to, but not killed by, predators have decreased survival when exposed to entomopathogens in the soil during the pupal stage. This suggests that predators can increase CPB mortality by non-lethal means. However, few studies have shown how both abiotic and biotic stressors might interact to influence pest fitness. Here we investigated the combined effects of warming temperatures (an abiotic stress) and predation (a biotic stress) on the fitness of CPB populations. We conducted a large-scale factorial field experiment that exposed CPB larvae to two temperature treatments (ambient or warmed) and two predation treatments (predators present or absent). Surviving larvae were then exposed to entomopathogenic nematodes while pupating in the soil to determine if abiotic and biotic stress experienced during the larvae stage affected survival to adulthood. We found that stress imposed by warming temperatures or predators resulted in decreases survival during the pupal stage. However, there was no interaction between the presence of predators and warming temperatures on CPB survival. Thus, the biotic and abiotic stresses acted independently to affect CPB survival. Our work sheds light into the role that both abiotic and biotic stress might influence pest populations.