Physiological benefits of nectar-feeding by a predatory beetle

Authors: Lundgren, Jonathan; SEAGRAVES, MICHAEL - Driscoll'S

Submitted to: Biological Journal of the Linnean Society, London
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/25/2011
Publication Date: 10/18/2011
Citation: Lundgren, J.G., Seagraves, M. 2011. Physiological benefits of nectar-feeding by a predatory beetle. Biological Journal of the Linnean Society, London. 104:661-669.

Interpretive Summary: Many beneficial insects like predators rely on nectar as an important component of their diet. Currently, it is unclear whether sugar feeding of this nature has physiological benefits for predatory insects; this is because nectar is deficient in lipids and proteins, two nutrients critical to maximum performance of these predators. We tested various ways that the lady beetle, Coleomegilla maculata, uses extrafloral nectar from faba beans to improve their survival, egg production, and glycogen and lipid reserves (two important storage nutrients). We found that consuming nectar soon after emergence had dramatic and lasting effects on lady beetle survival and reproduction. The beetles survived well on the sugar versus on plants without extrafloral nectaries. The nectar allowed the beetles to “prime” their reproductive systems for when high-quality diets become available. They were able to retain larger oocytes (egg precursors) in their ovaries because of sugar, and laid more eggs and had larger oocytes once high quality foods became available. In part, we found that these benefits were likely because the beetles used the sugar for physiological maintenance instead of their glycogen reserves, and these reserves did not have to be replenished prior to reproduction when high quality diets became available. Our observations support reports from the field that document a high frequency of sugar consumption in lady beetles, and provide some physiological mechanisms for why these predators readily consume this non-prey food.

Technical Abstract: Extrafloral nectar is an important food source for many animals, including predatory lady beetles (Coleoptera: Coccinellidae), although the physiological benefits of nectar consumption are poorly understood for most consumers. Under laboratory conditions, we confined new females of Coleomegilla maculata, a North American lady beetle, to Vicia faba plants with or without extrafloral nectaries for 10 d; after this the beetles were moved onto high-quality diet for an additional 15 d. Survival, fecundity, and oocyte size and development before and after consuming high quality diet were compared between treatments. Colorimetric assays were used to quantify the glycogen and lipid reserves of the beetles before and after exposure to high quality diet. Extrafloral nectar increased survival of C. maculata by 50%, and increased fecundity by 30% over starved individuals. Oocytes prior to and following exposure to high quality diet were significantly larger in females fed nectar than those without. Finally, glycogen reserves were higher following the prey-free period in the nectar-fed treatment than the starved treatment, but this deficiency did not persist once high quality diet was provided. We conclude that nectar improves survival and nutrient reserves of predators during periods of prey scarcity, and nectar during these periods improves the long term reproductive capacity of predators.