Prey foraging movements by Hippodamia convergens in wheat are influenced by hunger and aphids

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: 3/15/2013
Publication Date: 6/1/2013
Citation: Elliott, N.C., Kieckhefer, R.W., Phoofolo, M.W. 2013. Prey foraging movements by Hippodamia convergens in wheat are influenced by hunger and aphids. Southwestern Entomologist. 38(2):163-172.

Interpretive Summary: Lady bird beetles are important predators of cereal aphids and sometimes exert effective biological control of them. However, effective biological control is inconsistent and the reasons for the inconsistent control are not understood. This study was done to contribute information on the predator-prey relationship between lady bird beetles and cereal aphids, with the intent of providing new knowledge to help elucidate the conditions under which effective biological control will occur. We investigated foraging by adult convergent lady beetles, Hippodamia convergens, on cereal aphids on wheat growing in 1.8 x 1.8 m plantings in a greenhouse with a soil floor. The wheat was planted to simulate a typical production wheat field. One planting was infested with English grain aphids, whereas the other planting was not infested. Beetles were maintained on one of two feeding regimes, partially starved (light fed) and fed excess aphids (heavy fed). There were marked differences in the foraging movements by the beetles in the plots with and without aphids, and between light fed and heavy fed beetles. The reduced flight frequency and reduced rate of movement by walking observed in this study for light fed beetles compared to heavy fed beetles may be significant in assessing the potential for effective aphid biological control. The reduced dispersal rates, presumably resulting from insufficient energy levels for optimal dispersal, would reduce the likelihood that the beetles could find and exploit patchily distributed aphid infestations. When considered from the viewpoint of beetles exploiting aphids within an agricultural landscape, the outcome would be less than optimal biological control.

Technical Abstract: We investigated foraging movements by adult female convergent lady beetles, Hippodamia convergens Guerin-Meneville, on English grain aphids, 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 wheat field. One planting was infested with English grain aphids, whereas the other planting was not infested. Beetles were maintained on one of two feeding regimes, partially starved (light fed) and fed excess aphids (heavy fed). Light and heavy fed beetles moved nearly the same distance per minute in the absence of aphids. However, in the aphid infested plot light fed beetles moved a shorter distance than heavy fed beetles. The number of turns a beetle made per minute was greater for heavy fed than light fed beetles in both the aphid free and aphid infested plots. Light fed beetles flew less frequently than heavy fed beetles in both aphid infested and non-infested plots. Both light fed and heavy fed beetles flew less frequently in the aphid infested than in the non-infested plots. The horizontal distance traversed by beetles, presumed to be related to prey searching, was affected by the presence of aphids, the feeding regime (presumed to determine the physiological state of the beetles), and temperature. The reduced flight frequency and reduced rate of movement by walking observed in this study for light fed beetles may be significant in assessing the potential for H. convergens to exert effective aphid biological control. The reduced dispersal rates, presumably resulting from insufficient energy levels for optimal dispersal, would reduce the likelihood that adult H. convergens will find and exploit patchily distributed aphid infestations. When considered from the viewpoint of a population of beetles exploiting aphids within a landscape, the outcome would be less than optimal biological control.