Submitted to: Journal of Kansas Entomological Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/17/2008
Publication Date: 1/1/2009
Citation: Chege, P.G., Clark, T.L., Hibbard, B.E. 2009. Initial Larval Feeding on an Alternate Host Enhances Western Corn Rootworm (Coleoptera: Chrysomelidae) Beetle Emergence on Cry3Bb1-Expressing Maize. Journal of Kansas Entomological Society. 82(1):63-75. Interpretive Summary: The registration of transgenic corn with resistance to corn rootworm larval feeding offers a viable alternative to insecticides for managing the most economically important insect pests of corn. Maintaining susceptibility to transgenic crops (resistance management) is in the interest of growers, the Environmental Protection Agency, and industry, but requires an understanding of corn rootworm biology (such as an understanding of the interactions of alternate hosts and transgenic corn) that does not currently exist. To determine the impact of initial feeding of rootworm larvae on alternate hosts, followed by feeding on transgenic corn, two weed species (large crabgrass and giant foxtail), were infested along with rootworm-resistant transgenic corn and its nontransgenic original line (isoline) with corn rootworm larvae. After 5, 10, or 15 days, surviving larvae were transferred to final hosts (transgenic corn or its isoline). Significantly more beetles were produced from larvae that fed on an alternate host before moving to transgenic corn than from larvae fed exclusively on transgenic corn. Since partial development on an alternate host could affect the durability of transgenic corn, this information will be important to seed companies, the Environmental Protection Agency, and modelers in their attempts to develop resistance management plans for transgenic corn.
Technical Abstract: The potential for rootworm larvae to move between grassy weeds and transgenic maize may be important in resistance management of transgenic rootworm-resistant maize. To determine the impact of initial feeding of rootworm larvae on alternate hosts, followed by switching host to transgenic maize, on the development of western corn rootworm (Diabrotica virgifera virgifera LeConte), a split-split-plot randomized complete block design experiment was conducted under growth chamber and greenhouse conditions. Two weed species, large crabgrass, Digitaria sanguinalis (L.) Scop, giant foxtail, Setaria faberi R. A. W. Herrm, rootworm-resistant Cry3Bb1 transgenic maize (MON863, YieldGard® Rootworm) and its isoline, were infested with 50 neonate larvae per container 4 weeks after planting. On the 5th, 10th, and 15th d after infestation, a modification of the Tullgren funnel technique was used to facilitate larval movement (host-switching) from the original host plants to the final hosts (MON863 or its isoline). Beetle emergence and fecundity were significantly impacted by the original, the final host, and the interaction between the two effects. The original and the final host plant also impacted the sex ratio significantly. The host-switching date did not impact any of those three variables. Only the original host plant effect had a significant impact on egg viability. Significantly more reproductively fit beetles were produced from larvae that fed on an alternate host before moving to transgenic maize than from larvae fed exclusively on transgenic maize. Interactions with alternate hosts may influence transgenic maize resistance management models.