Insect predator odors protect herbivore from fungal infection

Abstract

Lethal predators and pathogens can reduce the size of pest populations and help regulate crop-damaging herbivores. Additionally, predators like the spined soldier bug (Podisus maculiventris) can elicit non-consumptive effects in herbivores such as the Colorado potato beetle (Leptinotarsa decemlineata), causing changes in prey behavior, physiology and life history. While it is known that lethal predators and pathogens interact, there is little known about the interaction of predator-induced non-consumptive effects and pathogens on their shared hosts. Using the spined soldier bug, which is known to elicit non-consumptive effects on potato beetles (e.g. reduced feeding), we studied the interaction of predator-induced non-consumptive effects and the fungal pathogen Beauveria bassiana on the survival of Colorado potato beetle larvae. In laboratory microcosms we found a 16–50% increase in survival of fungus-treated beetles held with non-lethal male stink bugs. We also studied the predator-fungus interaction on jasmonic acid-treated plants to assess whether elevated levels of host plant defenses made larvae more susceptible to fungal infection. Beetles’ susceptibility to fungal infection did not change when provided jasmonic-acid treated foliage as food. Finally, we determined that two volatile compounds (E-2-hexenal and alpha-terpineol), produced as part of the bugs’ aggregation pheromone, reduced conidial germination, resulting in higher levels of beetle survival. Our findings suggest that stink bug odors protect prey against fungal pathogens.