Effect of Cry3Bb Bt Corn and Tefluthrin on Postdispersal Weed Seed Predation

Indirect effects of insect control strategies on weed populations are important to consider when developing robust integrated pest management strategies. Weed seed predation rates were investigated in corn managed under three contrasting treatments based on control practices for corn rootworm: (1) the transgenic crop Cry3Bb Bt corn, (2) the broad-spectrum insecticide tefluthrin, and (3) no insecticide control. This 2-yr field study conducted near Ithaca, NY, involved quantifying seed loss from velvetleaf, common lambsquarters, and giant foxtail in arenas with and without vertebrate exclosures. Velvetleaf and giant foxtail were unaffected by the insecticide treatment; however, average seed predation of common lambsquarters was lower in both the Bt corn (11.9%) and insecticidetreated plots (11.8%) compared with control plots (17.5%) that did not receive any insecticide. Seed predation of common lambsquarters was not affected by the vertebrate exclosure. Lower seed predation in the transgenic Bt corn and insecticide treatments was likely due to nontarget effects on carabids (Coleoptera: Carabidae). Although the reduction in seed predation was modest and limited to only one of the three weed species tested, our results highlight the need for greater risk assessment that includes the ecosystem service of weed seed predation when considering insect pest management options. Nomenclature: Common lambsquarters, Chenopodium album L. CHEAL; corn rootworm, Diabrotica spp.; giant foxtail, Setaria faberi Herm. SETFA; velvetleaf, Abutilon theophrasti Medik. ABUTH; corn, Zea mays L; Bacillus thuringiensis var. kumamotoensis.