Measuring rootworm refuge function: Diabrotica virgifera virgifera emergence and mating in seed blend and strip refuges for Bacillus thuringiensis (Bt) maize

Aseasonal, undirected migration in insects: 'Invisible' but common

Many insect pests are long-distance migrants, moving from lower latitudes where they overwinter to higher latitudes in spring to exploit superabundant, but seasonally ephemeral, host crops. These seasonal long-distance migration events are relatively easy to recognize, and justifiably garner much research attention. Evidence indicates several pest species that overwinter in diapause, and thus inhabit a year-round range, also engage in migratory flight, which is somewhat "invisible" because displacement is nondirectional and terminates among conspecifics. Support for aseasonal, undirected migration is related to recognizing true migratory flight behavior, which differs fundamentally from most other kinds of flight in that it is nonappetitive. Migrating adults are not searching for resources and migratory flight is not arrested by encounters with potential resources. The population-level consequence of aseasonal, undirected migration is spatial mixing of individuals within the larger metapopulation, which has important implications for population dynamics, gene flow, pest management, and insect resistance management.

Movement Ecology of Adult Western Corn Rootworm: Implications for Management

Movement of adult western corn rootworm, Diabrotica virgifera virgifera LeConte, is of fundamental importance to this species' population dynamics, ecology, evolution, and interactions with its environment, including cultivated cornfields. Realistic parameterization of dispersal components of models is needed to predict rates of range expansion, development, and spread of resistance to control measures and improve pest and resistance management strategies. However, a coherent understanding of western corn rootworm movement ecology has remained elusive because of conflicting evidence for both short- and long-distance lifetime dispersal, a type of dilemma observed in many species called Reid's paradox. Attempts to resolve this paradox using population genetic strategies to estimate rates of gene flow over space likewise imply greater dispersal distances than direct observations of short-range movement suggest, a dilemma called Slatkin's paradox. Based on the wide-array of available evidence, we present a conceptual model of adult western corn rootworm movement ecology under the premise it is a partially migratory species. We propose that rootworm populations consist of two behavioral phenotypes, resident and migrant. Both engage in local, appetitive flights, but only the migrant phenotype also makes non-appetitive migratory flights, resulting in observed patterns of bimodal dispersal distances and resolution of Reid's and Slatkin's paradoxes.

Removing neonicotinoid seed treatments has negligible effects on refuge function and crop protection in transgenic maize targeting western corn rootworm (Coleoptera: Chrysomelidae)

Nearly all maize seed sold in the United States 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 1 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 a stable isotope (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 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 that 5% blends are serving little benefit for IRM. Plant stand and yield were not improved by NSTs.

IPM reduces insecticide applications by 95% while maintaining or enhancing crop yields through wild pollinator conservation

Environmental damage from insecticide overuse is a major concern, particularly for conservation of “good” insects such as pollinators that ensure stable production of food crops like fruits and vegetables. However, insecticides are also necessary for farmers to manage “bad” insects (i.e., pests), and thus, a more holistic view of crop management needs to account for the proper balance between the beneficial and detrimental aspects of pesticides. Here, we used multiyear field experiments with a paired corn–watermelon cropping system to show that insecticide use can be dramatically reduced (by ∼95%) while maintaining or even increasing yields through the conservation of wild bees as crop pollinators. These data demonstrate that food production and ecosystem sustainability are not necessarily conflicting goals.

Pest management practices in modern industrial agriculture have increasingly relied on insurance-based insecticides such as seed treatments that are poorly correlated with pest density or crop damage. This approach, combined with high invertebrate toxicity for newer products like neonicotinoids, makes it challenging to conserve beneficial insects and the services that they provide. We used a 4-y experiment using commercial-scale fields replicated across multiple sites in the midwestern United States to evaluate the consequences of adopting integrated pest management (IPM) using pest thresholds compared with standard conventional management (CM). To do so, we employed a systems approach that integrated coproduction of a regionally dominant row crop (corn) with a pollinator-dependent specialty crop (watermelon). Pest populations, pollination rates, crop yields, and system profitability were measured. Despite higher pest densities and/or damage in both crops, IPM-managed pests rarely reached economic thresholds, resulting in 95% lower insecticide use (97 versus 4 treatments in CM and IPM, respectively, across all sites, crops, and years). In IPM corn, the absence of a neonicotinoid seed treatment had no impact on yields, whereas IPM watermelon experienced a 129% increase in flower visitation rate by pollinators, resulting in 26% higher yields. The pollinator-enhancement effect under IPM management was mediated entirely by wild bees; foraging by managed honey bees was unaffected by treatments and, overall, did not correlate with crop yield. This proof-of-concept experiment mimicking on-farm practices illustrates that cropping systems in major agricultural commodities can be redesigned via IPM to exploit ecosystem services without compromising, and in some cases increasing, yields.