Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/4/2008
Publication Date: 3/15/2009
Citation: Bernklau, E.J., Meils, L.N., Coudron, T.A., Lim, E., Bjostad, L.B., Hibbard, B.E. 2009. Localized Search Cues in Corn Roots for Western Corn Rootworm Larvae (Coleoptera: Chrysomelidae). Journal of Economic Entomology. 102(2):558-562. Interpretive Summary: The western corn rootworm (WCR) is a major insect pest in continuous corn production. By feeding on corn roots, WCR causes economic losses due to plant lodging and decreased nutrient uptake, both resulting in yield loss. Currently, insecticides and transgenic corn are the only available options for its control under continuous corn production. Host-recognition cues that elicit a unique “tight-turning” behavior by WCR larvae were extracted from living corn roots with acetone. In behavioral bioassays, an acetone extract of corn roots caused larvae to exhibit a unique “tight-turning” behavior that is indicative of host recognition. The responses of larvae to the acetone extract were not significantly different from the responses to live corn roots, indicating that the compounds responsible for the tight-turning behavior are present in the extract. Separation of the active compounds from living tissue is an important step towards the identification of the compounds. Identification of host recognition cues may have practical implications in rootworm control. Compounds that elicit host recognition by WCR larvae might enhance the effectiveness of granular insecticide formulations and provide control of WCR damage with a reduced amount of insecticide. Alternatively, it may be possible to reduce or eliminate key host recognition compounds from corn roots through plant breeding and thereby protect corn roots from rootworm damage.
Technical Abstract: Host-recognition cues that elicit a unique “tight-turning” behavior by larvae of the western corn rootworm, Diabrotica virgifera virgifera LeConte, were extracted from living corn roots with acetone. In behavioral bioassays, an acetone extract of corn roots had activity in the tight-turning bioassay that was not significantly different from the activity of live corn roots, indicating that the compounds responsible for the tight-turning behavior are present in the extract. The Noldus EthoVision camera and software was used to record paths taken by larvae after exposure to a treatment. The paths were analyzed by measuring four parameters of movement: mean turn angle, mean meander, total distance, and maximum distance from origin. The tracks created by larvae after exposure to an acetone extract of corn roots were not significantly different from the tracks of larvae exposed to live corn roots for all four parameters. In a separate experiment, larvae exposed to corn root pieces or corn root liquid created the tight-turning tracks, but larvae exposed to root parts and liquids of oats (non-host) produced tracks similar to the control.