Omnivory in predatory lady beetles is widespread and driven by an appetite for sterols

Authors: UGINE, TODD - Cornell University; KRASNOFF, STUART - Retired ARS Employee; LOSEY, JOHN - Cornell University; BEHMER, SPENCER - Texas A&M University

Submitted to: Functional Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/14/2021
Publication Date: 2/2/2022
Citation: Ugine, T., Krasnoff, S., Losey, J., Behmer, S.T. 2022. Omnivory in predatory lady beetles is widespread and driven by an appetite for sterols. Functional Ecology. 36(2):458-470. https://doi.org/10.1111/1365-2435.13965.
DOI: https://doi.org/10.1111/1365-2435.13965

Interpretive Summary: Ladybugs are abundant predators that help control disease-vectoring pest insects, like aphids, in our forage, fiber and field crops, orchards and vineyards. The sevenspotted ladybug’s fitness is partially determined by eating sterols like cholesterol. This beetle species will eat small amounts of plant leaves and stems when they are sterol-limited to obtain sterols. However, it is not known if all ladybug species consume plants when they require sterols or how ladybugs detect and respond to different kinds of sterols. Results showed that many ladybug species, but not all, eat plants to obtain sterols. We found that beetles choose to eat certain sterols, indicating that they may select foods containing preferred sterols. Finally, we found that lady beetles use their labial palps to taste sterols and can do so at exceedingly low concentrations. No animals have been reported to have the ability to taste sterols. Taken together, these results show how ladybugs regulate their nutrient intake and provide key insights into the co-evolution of ladybugs and their aphid prey.

Technical Abstract: Lady beetles are globally distributed predators of insect herbivores. Adult sevenspotted lady beetles maintain a state-dependent sterol appetite and consume plant tissues to obtain sterols, which improves their fitness. Sterols are essential micronutrients that all animals need to survive. All six beetle species we tested maintained a state-dependent appetite for sterols. Sterol structure affected beetles’ propensity to feed on sterols, indicating that the number and position of double bonds in sterol molecules affects beetles’ ability to detect or desire to feed on them. Only some species fed on plant foliage in response to sterol-limitation, and few beetles supplemented with sterols consumed plant tissue. Beetles’ sterol appetite first appeared during the second larval stadium, and the rate of sterol consumption increased with age. Ablations of sensory organs revealed that beetles use their labial palps to detect sterols, and can do so at concentrations as low as 1.5 ppm. These data demonstrate that predatory lady beetles maintain a state-dependent appetite for an essential class of micronutrients. They also provide strong evidence that lady beetles can taste sterols, raising the possibility that they maintain novel as-yet undescribed gustatory receptors for an essential class of lipids.