Smelling danger: Lady beetle odors affect aphid population abundance and feeding, but not movement between plants

Predator-prey interactions are complex ecological interactions that influence community structure and function. Predators affect prey density directly by consuming and removing prey from the environment. Additionally, predators can elicit non-consumptive effects in prey which influence prey survival by altering prey behavior and physiology. Key to understanding the consequences of non-consumptive effects for prey populations is determining mechanisms of detection of predation risk. With insects, olfactory cues are commonly used to convey information. It has been shown that insect prey may eavesdrop on predator odor cues as a means to determine predation risk. Herein, we assessed whether the volatile odors of the predatory insect Harmonia axyridis (multicolored Asian lady beetle) affect the behavior (feeding and dispersal behaviors) and performance (population abundance) of aphids (Myzus persicae). Aphids reduced phloem ingestion when feeding in close proximity to lady beetle cues, however, predator odors did not drive aphids to relocate on plants or to disperse across plants away from the odor source. The lack of dispersal we observed is in contrast to studies that show increased aphid movement in the presence of predators that can make physical contact with the aphids. We also found that lady beetle odor cues had a population-level effect on aphids, with 25% reduction in aphid population abundance in the presence of the odor cues. This study highlights that anti-predator strategies may differ depending on the mechanism of detection of predation risk (i.e. olfactory versus physical stimuli), or the context in which they experience them, and raises the question of whether anti-predator responses observed are maladaptive or beneficial to aphid survival. These conclusions are critical for both our basic understanding of the mechanisms driving predator-prey interactions as well as providing insight into pest-natural enemy interactions within agricultural landscapes.