Physiological benefits of nectar feeding by a predatory beetle

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 days; after this, the beetles were moved onto a high-quality diet for an additional 15 days. Survival, fecundity, and oocyte size and development before and after consuming a 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 a high-quality diet. Extrafloral nectar increased the survival of C. maculata by 50%, and increased fecundity by 30%, over starved individuals. Oocytes prior to and following exposure to a high-quality diet were significantly larger in females fed nectar than in females that were not fed nectar. 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 a high-quality diet was provided. We conclude that nectar improves the survival and nutrient reserves of predators during periods of prey scarcity, and that the availability of nectar during these periods improves the long-term reproductive capacity of predators. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 104, 661–669.