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Title: Functional response of Hippodamia convergens to Sitobion avenae on wheat plants in the laboratory

Author
item Elliott, Norman - Norm
item KIECKHEFER, ROBERT - Retired ARS Employee
item PHOOFOLO, MPHO - National University Of Lesotho

Submitted to: Southwestern Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/15/2011
Publication Date: 12/1/2011
Citation: Elliott, N.C., Kieckhefer, R.W., Phoofolo, M.W. 2011. Functional response of Hippodamia convergens to Sitobion avenae on wheat plants in the laboratory. Southwestern Entomologist. 36(4):423-431.

Interpretive Summary: Lady beetles are important predators of aphids in several agricultural crops. We investigated predation by lady beetles on cereal aphids on wheat plants in a laboratory arena and developed a mathematical model to describe the relationship between the number of aphids eaten, the hunger level of the beetles, and the number of aphids on a wheat plant. We observed the foraging activity of 56 female lady beetles and a combined total of 1167 plant visits by those beetles. Beetle hunger and the number of aphids per plant were significantly correlated with the time spent searching a wheat plant and the number of aphids eaten during the plant visit. Partial correlation coefficients for hunger after adjusting for the effect of the number of aphids per plant were not significant for the time spent searching a plant or for the number of aphids eaten during a plant visit. Among the variables measured, knowledge of the number of aphids per plant was sufficient for predicting searching time and predation. A mathematical model of foraging was developed and tested, and showed no statistically significant bias indicating that the model provided a reasonable description of the foraging process. The importance of the model is in helping to understand foraging by lady beetles in wheat and in helping predict levels of biological control of aphids by lady beetles in wheat.

Technical Abstract: We investigated predation by adult convergent lady beetle, Hippodamia convergens Guerin-Meneville, on English grain aphid, Sitobion avenae L., on wheat, Triticum aestivum L., plants in a laboratory arena and developed a functional response model for the number of aphids eaten by an adult female convergent lady beetle. We observed the foraging activity of 56 female convergent lady beetles, and a combined total of 1167 plant visits by those beetles. Beetle hunger and the number of aphids per plant were significantly correlated with the time spent searching a wheat plant and the number of aphids eaten during the plant visit. Partial correlation coefficients for hunger after adjusting for the effect of the number of aphids per plant were not significant for the time spent searching a plant or for the number of aphids eaten during a plant visit. Among the variables measured, knowledge of the number of aphids per plant was sufficient for predicting searching time and predation. A Holling Type II functional response model was developed and tested for convergent lady beetles foraging on English grain aphids. Comparison of the expected proportion of English grain aphids eaten versus the observed proportion eaten showed that there was no statistically significant bias in model predictions indicating that the model provided a reasonable description of the functional response, however, high variation in observed versus predicted predation rates were evident, which may reflect the inherent high variability in all aspects of the foraging process by the beetles.