Frass Analysis of Diets of Aphidophagous Lady Beetles (Coleoptera: Coccinellidae) in Utah Alfalfa Fields

Abstract

Aphidophagous lady beetles enhance their foraging success in natural settings by consuming other types of food in addition to aphids. Frass analysis was used to examine natural diets of female lady beetles in fields of alfalfa (Medicago sativa L.) in northern Utah. The first (spring) alfalfa crop was censused in 2004 and 2005 to determine the diet of female adults of the introduced Coccinella septempunctata L., and two native species, C. transversoguttata richardsoni Brown, and Hippodamia convergens Guerin. The proportion of females of the three lady beetle species that fed on pea aphids [Acyrthosiphon pisum (Harris)] and alfalfa weevil larvae [Hypera postica (Gyllenhal), an abundant alternative prey] increased from early to late season during the first crop. A corresponding seasonal decrease occurred in the proportion of females consuming other types of arthropods (e.g., thrips and collembolans) and nonarthropod food (pollen and fungal spores). Overall, frass analysis indicated that the diets of C. septempunctata and the two native species in alfalfa were similar in their inclusion of a broad variety of foods. The study shows that frass analysis can provide a good overview of the diets of lady beetles in natural settings.