Shelby J. Fleischer

Areawide Suppression of European Corn Borer with Bt Maize Reaps Savings to Non-Bt Maize Growers

Economic Benefits of Bt Maize Maize containing a transgenically expressed toxin originating from Bacillus thuringiensis (Bt maize) is planted across the United States to combat insect herbivory. Non-Bt Maize is also planted alongside Bt maize fields to provide refuges for the insects, which helps to prevent resistance to Bt maize from evolving. Hutchison et al. (p. 222; see the Perspective by Tabashnik) analyzed how Bt maize affected the economic impact of the European corn borer moth in the midwestern United States, as well as its population dynamics. Larval density, a predictor of corn borer population size, has dropped in correlation with the percentage of Bt maize planted. In the highest Bt maize producing state, the positive effects of Bt maize in controlling insect herbivore populations extended to non-Bt maize. Furthermore, the decrease in insect populations demonstrated an overall economic benefit outweighing the overall extra costs associated with planting Bt maize. Genetically modified maize generally reduces insect populations to relieve pest pressure on unmodified neighboring crops. Transgenic maize engineered to express insecticidal proteins from the bacterium Bacillus thuringiensis (Bt) has become widely adopted in U.S. agriculture. In 2009, Bt maize was planted on more than 22.2 million hectares, constituting 63% of the U.S. crop. Using statistical analysis of per capita growth rate estimates, we found that areawide suppression of the primary pest Ostrinia nubilalis (European corn borer) is associated with Bt maize use. Cumulative benefits over 14 years are an estimated

Sampling in Precision IPM: When the Objective Is a Map

3.2 billion for maize growers in Illinois, Minnesota, and Wisconsin, with more than

Toxic and Behavioral Effects to Carabidae of Seed Treatments Used on Cry3Bb1- and Cry1Ab/c-Protected Corn

2.4 billion of this total accruing to non-Bt maize growers. Comparable estimates for Iowa and Nebraska are

Dynamics in the Spatial Structure of Leptinotarsa decemlineata (Coleoptera: Chrysomelidae)

3.6 billion in total, with

Spatial and Temporal Dynamics of Colorado Potato Beetle (Coleoptera: Chrysomelidae) in Fields with Perimeter and Spatially Targeted Insecticides

1.9 billion for non-Bt maize growers. These results affirm theoretical predictions of pest population suppression and highlight economic incentives for growers to maintain non-Bt maize refugia for sustainable insect resistance management.

Transmission Efficiency of Cucumber mosaic virus by Aphids Associated with Virus Epidemics in Snap Bean

ABSTRACT Measuring and understanding spatial variation of pests is a fundamental component of population dynamics. The resulting maps can drive spatially variable pest management, which we define as precision integrated pest management (IPM). Precision IPM has the potential to reduce insecticide use and slow the rate of resistance development because of the creation of temporally dynamic refuges. This approach to IPM requires sampling in which the objective is to measure spatial variation and map pest density or pressure. Interpolation of spatially referenced data is reviewed, and the influence of sampling design is suggested to be critical to the mapped visualization. Spatial sampling created problems with poor precision and small sample sizes that were partially alleviated with choosing sampling units based on their geostatistical properties, adopting global positioning system technology, and mapping local means. Mapping the probability of exceeding a threshold with indicator kriging is discussed as a decision-making tool for precision IPM. The different types of sampling patterns to deploy are discussed relative to the pest mapping objective.

Transgenes Sustain Epigeal Insect Biodiversity in Diversified Vegetable Farm Systems

Abstract Most transgenic corn seed is now treated with systemic neonicotinoid insecticides. To address potential direct nontarget effects of these combined technologies, 16 Carabidae species from 10 genera (Agonum, Amara, Anisodactylus, Bembidion, Chlaenius, Harpalus, Patrobus, Poecilus, Pterostichus, and Scarites) field-collected from corn were directly exposed to Bacillus thuringiensis (Bt) Cry toxin-laden pollens and seed treatments in feeding and defined-dose bioassays. All adults readily fed on field or sweet corn pollens that expressed coleopteran-specific Cry3Bb1 or lepidopteran-targeting Cry1Ab/c, and no significant toxicity was observed. Adult survivorship ranged from 47 d for the predator Pterostichus melanarius (Illiger) to a year for the more omnivorous Scarites quadriceps Chaudoir, feeding solely on pollen containing 30–90 μg Cry3Bb1/g and water. In contrast, commercial doses of neonicotinoid seed treatments (imidacloprid, thiamethoxam, or clothianidin) elicited nearly complete mortality for 18 carabid species in 4-d bioassays containing corn seedlings. Carabid consumption of fungicide-only (fludioxonil plus mefenoxam) seed treatments was generally observed within 1 d, compared with a 2-d latency on neonicotinoid treatments, suggesting an antifeedant effect of the insecticide. In microcosm bioassays containing a corn seedling and five prey, clothianidin seed treatments killed adult western corn rootworm, Diabrotica virgifera virgifera LeConte and S. quadriceps, although the smaller Harpalus pensylvanicus (DeGeer) was more tolerant. We conclude that the neonicotinoid/fungicide seed treatments, and not Cry3Bb1 or CryIAb/c, are a major direct mortality factor for ground beetles. Field studies are needed to determine population and community level effects on Carabidae when these transgenic and seed-treatment technologies are combined.

Coupling Developmental Physiology, Photoperiod, and Temperature to Model Phenology and Dynamics of an Invasive Heteropteran, Halyomorpha halys

Abstract Integrating global positioning systems technology with a visual canopy survey, a 1-m level of sampling support was used to explore within-field spatial organization of the Colorado potato beetle, Leptinotarsa decemlineata (Say), in potatoes. Spatially referenced counts of adult and large larvae (third and fourth instar) L. decemlineata were made in four ≈1.5-ha untreated potato fields during two Pennsylvania growing seasons. The presence and nature of spatial structure varied with developmental stage. Overwintered, immigrating adults established ‘trends’ or ‘drift’ in the mean density, but spatial dependency (covariance structure) was not detected. This, coupled with a high incidence-to-mean density relationship, suggests a within-field dispersive role for the colonizers. Large larvae and F1 adults, in contrast, displayed spatial dependency (covariance structure), at times accounting for up to ≈45% of the variation. Their relatively lower incidence-to-mean density relationship suggests less within-field mobility during the reproductive phase of the population cycle. These observations imply that, although an insect population’s spatial structure may be difficult to characterize due to its dynamic nature, there is a consistent and predictable pattern in L. decemlineata spatial structure that is linked to its population phenology.

Development and Life Table of Acalymma vittatum (Coleoptera: Chrysomelidae), a Vector of Erwinia tracheiphila in Cucurbits

Abstract Concern over insecticide resistance has led to the suggestion of spatially variable within-field management of Colorado potato beetle, Leptinotarsa decemlineata (Say). Here we compare L. decemlineata spatial and temporal dynamics, and potato yield, in fields treated with a narrow perimeter (5.5 m) of systemic imidacloprid supplemented with spatially targeted sprays to untreated fields and to fields where all rows received the systemic. The systemic targeted immigrating individuals which, having acquired the field through either flight or walking, first established themselves in the outer 5.5 m of the field. The perimeter treatment (≈25% of field area) reduced mean densities with no effect on timing of peak densities. Immigrating adults established similar spatial trends in both perimeter and untreated fields. Although trends in F1 larval densities have been shown to follow the patterns established by immigrating adults, trends in the F1 larval densities of the perimeter treatments diverged from adult patterns and developed highest densities in field centers. Immigrating adults had little to no spatial dependence in the covariance structure in any treatments. Spatial dependence in the covariance structure of F1 larval and F1 adult populations developed as density increased in both perimeter and untreated fields, with a tendency for increasing spatial dependence in perimeter fields, though this was not statistically significant. Comparing the perimeter to untreated fields, yields increased at a proportion that was higher than the proportion of land area treated, but remained significantly lower than the whole-field treatment. These results suggest that the perimeter tactic has promise as a site-specific resistance management program, but that refinement of border width is needed to optimize trade-offs among yield, quality, and long-term maintenance of susceptibility.

Herbaceous weeds are not ecologically important reservoirs of Erwinia tracheiphila

Cucumber mosaic virus (CMV) is a major component of the virus complex that has become more pronounced in snap bean in the midwestern and northeastern United States since 2001. Multiple-vector-transfer tests were done to estimate the CMV transmission efficiencies (p) of the main aphid species identified in commercial snap bean fields in New York and Pennsylvania. The four most efficient vectors (p > 0.05) were Aphis gossypii, A. glycines, Acyrthosiphon pisum, and Therioaphis trifolii, which were all significant species in the migratory aphid populations in snap bean. Moderately efficient vectors (0.01 < p < 0.04) were A. spiraecola, A. craccivora, Macrosiphum euphorbiae, and Rhopalosiphum maidis. Poor vectors (p < 0.01) included A. fabae, Nearctaphis bakeri, and Myzus persicae. Only one species, Sitobion avenae, failed to transmit CMV in replicated tests. Estimates of p were consistent between different clones of the same aphid species and among three different field isolates of CMV tested. Single-vector-transfer test results for a subset of the species supported those obtained via the multiple-vector-transfer approach. Our results are consistent with the notion that A. glycines is a major vector of recent CMV epidemics in snap bean, but that species is only one of several that are involved.