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Title: Foraging by Hippodamia convergens for cereal aphids on wheat plants in the laboratory

Author
item Elliott, Norman - Norm
item Kieckhefer, Robert
item PHOOFOLO, MPHO - National University Of Lesotho

Submitted to: Southwestern Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2010
Publication Date: 4/30/2011
Citation: Elliott, N.C., Kieckhefer, R.W., Phoofolo, M.W. 2011. Foraging by Hippodamia convergens for cereal aphids on wheat plants in the laboratory. Southwestern Entomologist. 36(1):1-10.

Interpretive Summary: We observed predation by adult lady beetles, Hippodamia convergens, on English grain aphids, Sitobion avenae, on wheat plants in a laboratory arena. A model relating beetle hunger to starvation time was developed and used to calculate initial hunger for beetles used in predation observations. Hunger level of the beetles had a weak but significant impact on virtually all aspects of the searching behavior of the beetles for their aphid prey. An important result of the research was that even though we observed increased residence time and increased time spent searching by adult lady beetles with increasing aphid density, the predation rate was independent of aphid density. The aphids are part of a complex of cereal aphids that are important pests of cereals. The importance of the work lies in establishing a detailed understanding of the predator-prey relationship between lady beetles and aphids so that levels of biological control of cereal aphids by lady beetles can be predicted.

Technical Abstract: We investigated predation by adult Hippodamia convergens Guerin-Meneville on the English grain aphid, Sitobion avenae L., on wheat plants in a laboratory arena. A model relating beetle hunger to starvation time was developed and was used to calculate initial hunger for beetles used in predation observations. Hunger level was significantly correlated with the time spent searching a wheat plant and the number of aphids that were eaten during the plant visit for both male and female H. convergens. Time since contacting an aphid (either touching or eating) was weakly negatively correlated with time spent searching a plant by H. convergens. Time since contact also had a weak negative influence on the number of aphids eaten. The mean time required to eat an aphid increased with aphid instar as was expected because of the corresponding increase in size. Female H. convergens took an average of 27.0 sec to consume a 1st instar S. avenae, with time increasing to 141.2 sec for an apterous adult. The mean proportion of S. avenae leaving a plant in response to beetle foraging increased with aphid instar from 0.09 for 1st instar to 0.49 for adult alatae. The proportion of aphids leaving a plant was significantly correlated with the time spent searching a plant by a beetle. Even though we observed increased residence time and increased time spent searching by adult H. convergens with increasing aphid density, the predation rate was independent of aphid density.