Why eat extra floral nectar? Understanding food selection by Coleomegilla maculata (Coleoptera: Coccinellidae)

Authors: Choate, Beth; Lundgren, Jonathan

Submitted to: BioControl
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/14/2012
Publication Date: 5/30/2013
Citation: Choate, B.A., Lundgren, J.G. 2013. Why eat extra floral nectar? Understanding food selection by Coleomegilla maculata (Coleoptera: Coccinellidae). Biocontrol. 58(3):359-367.

Interpretive Summary: Many insects previously considered strictly predaceous are actually omnivorous, feeding on both prey and plant or fungal material. In an effort to increase predator abundance throughout cropping systems in conjunction with biological control efforts, researchers have evaluated the role of non-prey foods, such as sugar and pollen. The decision-making process as to how individuals determine whether to consume prey or a non-prey food item remains largely unknown. Laboratory studies were conducted to develop a better understanding of the factors involved in decision-making. Female lady beetles fed on fewer aphid prey when they were given access to sugar in the form of extrafloral nectar, nectar not associated with flowers. Feeding on prey versus a mixed diet of prey and sugar had no obvious health or reproductive benefit for the beetles. In an effort to better understand the mechanism behind feeding on non-prey foods, studies to evaluate volatiles produced by the plant were conducted. These indicated that plant extrafloral nectaries are producing attractive odors or scents. Lady beetles chose plants with exposed nectaries more often than those with covered nectaries. Research must be conducted in the field in order to determine how a decrease in prey consumption and an increase in attraction will ultimately influence biological control. These results demonstrate an additional dimension to increasing biological control agents through the incorporation of non-prey foods and are important for future development of pest management programs by land managers and researchers.

Technical Abstract: The potential of omnivorous arthropods to stabilize ecosystems makes them an invaluable resource in biological control efforts. Methods of increasing predator abundance throughout agroecoystems include the incorporation of non-prey food items, yet the influence of this on predation rates remains unknown. In order to gain an understanding of sugar feeding in the predaceous beetle, Coleomegilla maculata, laboratory studies were conducted evaluating prey consumption in the presence of extrafloral nectaries. The physiology of beetles with access to prey only and a mixed diet were compared. To elucidate results of beetle physiology, Y-tube olfactometer studies were conducted and preferences between food types evaluated. Coleomegilla maculata females consumed significantly fewer aphids when sugar was available. Nutrient reserves and reproductive capability were not increased upon consumption of a mixed diet. Evaluation of predator behavior when offered both food resources together and separately demonstrated that extrafloral nectaries do produce attractive volatiles. These results provide invaluable insight into the feeding choices of omnivorous insects, suggesting that preference may be plant-mediated. Research must be conducted in the field in order to determine how a decrease in prey consumption and an increase in attraction will ultimately influence biological control.