Removing Neonicotinoid Seed Treatments Has Negligible Effects on Refuge Function and Crop Protection in Transgenic Maize Targeting Western Corn Rootworm (Coleoptera: Chrysomelidae)

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Entomological Society of America


Nearly all maize seed sold in the United States (US) includes a neonicotinoid seed treatment (NST), meant to protect seedlings against early-season insect pests. For key pests, including western corn rootworm (Diabrotica virgifera virgifera LeConte) (D.v.v), insecticidal proteins derived from Bacillus thuringiensis (Bt) are expressed in plant tissues as alternatives to soil-applied insecticides. Insect resistance management (IRM) plans use non-Bt “refuges” to encourage survival of Bt-susceptible D.v.v., which maintains susceptible alleles in the population. In non-cotton producing regions, IRM guidelines require a minimum 5% blended refuge for maize expressing more than one trait targeting D.v.v. Prior work has shown that 5% blends yield insufficient proportions of refuge beetles to contribute reliably to IRM. Whether NSTs interfere with survivorship of refuge beetles is unknown. Our objective was to determine whether NSTs affect proportions of refuge beetles, and secondarily, to determine whether NSTs provide agronomic advantages over Bt seed alone. To reveal host plant type (i.e., Bt or refuge), we used stable isotopes (15N) to mark refuge plants in plots with 5% seed blends. To assess refuge performance between treatments, we compared proportions of beetles from respective natal hosts. In all site-years, NSTs showed inconsistent, often negligible, effects on proportions of refuge beetles. Treatment comparisons showed inconsistent agronomic benefits of NSTs when combined with Bt traits. Our results demonstrate that NSTs have a negligible impact on refuge performance and reinforces the assertion 5% blends are serving little benefit for IRM. Plant stand and yield were not improved by NSTs.



Bacillus thuringiensis, Neonicotinoids, Insect resistance management