Assistant Professor Montana State University Bozeman, Montana
Climate change is causing an increase in drought events around the world. Water limitation affects the quality and quantity of plant resources for herbivorous insects, leading to cascading effects for higher trophic levels. Physiological changes due to water limitation are predicted to make plants more nutritious for insect herbivores, but it comes at the cost of increased plant defensive responses, declining biomass, and restricted access to the phloem. These changes in the plant have direct effects on natural enemies by changing the attractiveness of the habitat, and indirect effects by changing the quality of their prey. The goal of this study was to assess how drought stress affects behavioral interactions between the wasp (Aphidius colemani) and bird cherry-oat aphids (Rhopalosiphum padi). Our design is unique in that we incorporated a gradient of water stress intensity to assess insect response to mild water limitation. We found parasitic wasps had improved capacity to suppress aphid populations on drought-stressed plants. The mechanism is still unclear, as increased aphid suppression was not directly linked to increased wasp pupae (mummy) formation, so the increased suppression may be driven by a combination of consumptive and non-consumptive effects. Changes in the ability of natural enemies to suppress pest populations may impact the way we choose to manage agroecosystems under drought conditions.