Location: Emerging Pests and Pathogens ResearchTitle: Prey nutrient content creates omnivores out of predators
|UGINE, TODD - Cornell University|
|GREBENOK, ROBERT - Canisius College|
|BEHMER, SPENCER - Texas A&M University|
|LOSEY, JOHN - Cornell University|
Submitted to: Ecology Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/28/2018
Publication Date: 12/9/2018
Citation: Ugine, T., Krasnoff, S., Grebenok, R., Behmer, S., Losey, J. 2018. Prey nutrient content creates omnivores out of predators. Ecology Letters. 22:275-283.
Interpretive Summary: Lady beetles (AKA "Ladybugs") prey upon many economically important agricultural pest species' and therefore have been deployed in the field for natural pest control. Understanding the dietary requirements and preferences of lady beetles is critical to their exploitation as biological control agents. Many species of predators including lady beetles, are known to also consume non-prey foods. The forces that drive the shift of an animal from a predator to an herbivore are not well understood. Sterols (e.g. cholesterol) are essential nutrients for all animals. Arthropods, including insects, cannot make their own sterols and need to obtain them from their food. Because predators consume other animals, which putatively contain cholesterol, no predators are thought to be sterol-limited. This research showed that the predatory sevenspotted lady beetle cannot reproduce successfully when fed a diet consisting solely of aphids. It was further shown that the aphid species on which the lady beetles were reared (pea aphids) maintain exceedingly low concentrations of sterols in their body, and that plant sterols and cholesterol restores lady beetle reproduction. Additionally, lady beetles demonstrated an innate appetite for sterols and consume non-prey foods like plant foliage to increase their sterol intake and satisfy their metabolic needs.
Technical Abstract: The proximate forces that create omnivores out of herbivores and predators have long fascinated ecologists, but the causal reasons for a shift to omnivory are poorly understood. Determining what factors influence changes in trophic position is essential as omnivory plays a central role in theoretical and applied ecology. We used sevenspotted lady beetles (Coccinella septempunctata) to test how prey nutrient content affects beetles’ propensity to engage in herbivory. We show that beetles consuming an all-prey diet demonstrate normal growth and development, but suffer a complete loss of fitness (spermatogenic failure) that is restored via herbivory and supplementation with phytosterols and cholesterol. Furthermore, we show that lady beetles possess a state-dependent sterol-specific appetite and redressed their sterol deficit by feeding on foliage. These results demonstrate that predators balance their nutrient intake via herbivory when prey quality is low, and reveal a selective force (sterol nutrition) that drives predatory taxa to omnivory.