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 1,167 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 versus observed proportions of English grain aphids eaten showed no statistically significant bias in model predictions, thus indicating that the model provided a reasonable description of the functional response. However, variation in observed versus predicted predation rates was evident, which may reflect the inherent variability in all aspects of the foraging process by the beetles.
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Vol. 36 • No. 4