Foraging by Hippodamia convergens for the aphid Sitobion avenae on wheat plants growing in greenhouse plots

Authors: Elliott, Norman - Norm; KIECKHEFER, ROBERT - Retired ARS Employee; PHOOFOLO, MPHO - National University Of Lesotho

Submitted to: Southwestern Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2012
Publication Date: 12/1/2012
Citation: Elliott, N.C., Kieckhefer, R.L., Phoofolo, M.W. 2012. Foraging by Hippodamia convergens for the aphid Sitobion avenae on wheat plants growing in greenhouse plots. Southwestern Entomologist. 37(4):467-474.

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 greenhouse plots planted to wheat in such a way to simulate wheat in production fields of wheat. Beetles were observed foraging in the plot and movements of beetles on the plants and soil floor of the plot, the amount of time spent searching and eating were recorded, as were incidents when the beetle flew from one location to another in the plot, or flew out of the plot altogether. Air temperature, solar radiation intensity, wheat plant height, and aphid density were measured concomitant with foraging observations. The number of aphids eaten per minute increased with increasing air temperature and solar radiation intensity. The time required to eat an aphid was positively influenced by the number of aphids per tiller, while the proportion of time spent searching was not significantly related to any of the variables measured. After accounting for the effect of aphid density, the number of aphids eaten per minute in the greenhouse wheat plots did not differ significantly from the number eaten per minute in a laboratory arena study. Therefore, after adjusting the model to account for the effects of temperature, a model previously developed for predicting predation rate of beetles on cereal aphids in the laboratory arena was applicable for predicting predation in the greenhouse plots, and presumably also in the field. The importance of the results lies in achieving the ability to predict levels of biological control of aphids by lady beetles in wheat fields, and thereby incorporating the effects of naturally occurring biological control into pest management decision-making.

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., growing in 1.8 x 1.8 m plantings in a greenhouse with a soil floor. The wheat was planted to simulate wheat in a typical production field, with rows planted 15.2 cm apart and one seed planted per 2.5 cm within each row. The plot was artificially infested with aphids. Beetles in one group (designated light fed) were provided with 20 English grain aphids of mixed instars per day, whereas beetles in a second group (designated heavy fed) were provided with 80 English grain aphids per day for 4-6 days prior to observation. Beetles were observed foraging in the plot for a period of 12 minutes. For each visit to plants, and for movements of beetles on the soil floor of the plot, the amount of time spent searching and eating were recorded, as were incidents when the beetle flew from one location to another in the plot, or flew out of the plot altogether. Air temperature, solar radiation intensity, wheat plant height, and aphid density were measured concomitant with foraging observations. The number of aphids eaten per minute increased with increasing air temperature and solar radiation intensity. The time required to eat an aphid was positively influenced by the number of aphids per tiller, while the proportion of time spent searching was not significantly related to any of the variables measured. Light fed beetles ate a greater number of aphids per minute than heavy fed beetles. After accounting for the effect of aphid density, the number of aphids eaten per minute in the greenhouse wheat plots did not differ significantly from the number eaten per minute in a laboratory arena in a previously published laboratory study. The application of the results for developing a useful functional response model for H. convergens predation on aphids in production fields of wheat is discussed.