Applying an integrated refuge to manage western corn rootworm (Coleoptera: Chrysomelidae): effects on survival, fitness, and selection pressure.

The refuge strategy can delay resistance of insect pests to transgenic maize producing toxins from Bacillus thuringiensis (Bt). This is important for the western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), because of its history of adaptation to several management practices. A 2-yr study across four locations was conducted to measure the effects of integrated refuge (i.e., blended refuge) on western corn rootworm survival to adulthood, fitness characteristics, and susceptibility to Bt maize in the subsequent generation. The treatments tested in this study were as follows: a pure stand of Bt maize (event DAS-59122-7, which produces Bt toxins Cry34Ab1/Cry35Ab1), a pure stand of refuge (non-Bt maize), and two variations on an integrated refuge consisting of 94.4% Bt maize and 5.6% non-Bt maize. Within the two integrated refuge treatments, refuge seeds received a neonicotinoid insecticidal seed treatment of either 1.25 mg clothianidin per kernel or 0.25 mg thiamethoxam per kernel. Insects in the pure stand refuge treatment had greater survival to adulthood and earlier emergence than in all other treatments. Although fecundity, longevity, and head capsule width were reduced in treatments containing Bt maize for some site by year combinations, Bt maize did not have a significant effect on these factors when testing data across all sites and years. We found no differences in susceptibility of larval progeny to Bt maize in bioassays using progeny of adults collected from the four treatments.

Entomopathogenic Nematodes for Field Control of Onion Maggot (Delia antiqua) and Compatibility with Seed Treatments.

Onion maggot (Delia antiqua) is a prominent pest of allium crops in temperate zones worldwide. Management of this pest relies on prophylactic insecticide applications at planting that target the first generation. Because effective options are limited, growers are interested in novel tactics such as deployment of entomopathogenic nematodes. We surveyed muck soils where onions are typically grown to determine if entomopathogenic nematode species were present, and then evaluated the compatibility of entomopathogenic nematode species with the insecticides commonly used to manage D. antiqua. We also evaluated the efficacy of these entomopathogenic nematodes for reducing D. antiqua infestations in the field. No endemic entomopathogenic nematodes were detected in surveys of muck fields in New York. Compatibility assays indicated that, although insecticides such as spinosad and, to some extent, cyromazine did cause mortality of entomopathogenic nematodes, these insecticides did not affect infectivity of the entomopathogenic nematodes. Field trials indicated that applications of entomopathogenic nematodes can reduce the percentage of onion plants killed by D. antiqua from 6% to 30%. Entomopathogenic nematodes reduced D. antiqua damage and increased end of season yield over two field seasons. Applications of entomopathogenic nematodes may be a viable option for reducing D. antiqua populations in conventional and organic systems. Together with other management tactics, like insecticide seed treatments, applications of entomopathogenic nematodes can provide a yield boost and a commercially acceptable level of D. antiqua control.

Geographic Distribution of Bacillus thuringiensis Cry1F Toxin Resistance in Western Bean Cutworm (Lepidoptera: Noctuidae) Populations in the United States.

The western bean cutworm (WBC), Striacosta albicosta (Lepidoptera: Noctuidae), can be a severe pest of transgenic corn in the western Plains and Great Lakes regions of North America, including on hybrids expressing the Bacillus thuringiensis (Bt) Cry1F toxin. The level and geographic distribution of Cry1F resistance are not completely known. Neonate S. albicosta from 10 locations between Nebraska and New York state were subjected to dose-response trypsin-activated native Cry1F toxin overlay bioassays. In 2017, the mean estimated lethal concentration causing 50% larval mortality (LC50) ranged from 15.1 to 18.4 µg Cry1F cm-2, and were not significantly different among locations. In 2018, LC50 estimates at Scottsbluff, NE (22.0 µg Cry1F cm-2) and Watertown, NY (21.7 µg Cry1F cm-2) were significantly higher when compared to locations in Michigan (15.8 µg Cry1F cm-2). Significantly lower 14-day larval weight among survivors was correlated with higher Cry1F dose. Results from this study indicate that S. albicosta survivorship on purified Bt Cry1F toxin shows a relatively even distribution across the native and range expansion areas where seasonal field infestations typically occur.

Multiple-species natural enemy approach for biological control of alfalfa snout beetle (Coleoptera: Curculionidae) using entomopathogenic nematodes.

Multiple-species natural enemy approach for the biological control of the alfalfa snout beetle, Otiorhynchus ligustici (L.) (Coleoptera: Curculionidae), was compared with using single-species of natural enemies in the alfalfa ecosystem by using entomopathogenic nematodes with different dispersal and foraging behaviors. Steinernema carpocapsae NY001 (ambush nematode), Heterorhabditis bacteriophora Oswego (cruiser nematode), and Steinernema feltiae Valko (intermediate nematode) were applied in single-species, two-species combinations, and one three-species combination treatments at 2.5 x 10(9) infective juveniles per hectare. All nematode species persisted for a full year (357 d). S. carpocapsae NY001 protected the plants from root-feeding damage better than H. bacteriophora Oswego but allowed for higher larval survival than all other nematode treatments. S. feltiae Valko protected the plants better than H. bacteriophora Oswego and controlled alfalfa snout beetle larvae better than S. carpocapsae NY001. H. bacteriophora Oswego allowed for similar root damage compared with control plots but reduced larval populations better than S. carpocapsae NY001. The combination of S. carpocapsae NY001 and H. bacteriophora Oswego provided significantly better protection for the plants than the control (unlike H. bacteriophora Oswego alone) and reduced host larva survival more than S. carpocapsae NY001 alone. The combination S. feltiae Valko and H. bacteriophora Oswego could not be statistically separated from the performance of S. feltiae Valko applied alone.

Long-term Persistence of Native New York Entomopathogenic Nematode Isolates Across Crop Rotation.

Entompathogenic nematodes are found worldwide in a wide array of soil habitats with a broad host range and significant variation in foraging strategies. The primary use of entomopathogenic nematodes (EPNs) in managed plant systems has been focused on inundative releases in a biopesticide strategy. Little effort has been placed in investigating the use of natural occurring or adapted EPN strains for long-term suppression of pest outbreaks in managed systems. This study examined the potential of EPN isolates from Northern New York (NNY), inoculated at a low level (250 million IJ/ha), which are climate adapted and their persistent characteristics preserved to maintain population levels in agricultural fields (N = 82) for multiple years and across crop rotation (alfalfa:corn:alfalfa). Persistence levels for Steinernema carpocapsae (Weiser) (Rhabditida:Steinernematidae) ranged between 8 and 12% of the soil cores assayed in continuous alfalfa and 1-14% of the soil cores assayed in continuous corn rotated from EPN treated alfalfa. Steinernema feltiae (Filipjev) (Rhabditida: Steinernematidae) residual persistence level ranged between 17 and 32% in continuous alfalfa and 22-41% in continuous corn rotated from EPN treated alfalfa. Combined EPN level ranged between 27 and 43% of the soil cores in continuous alfalfa and 28-55% in continuous corn rotated from EPN-treated alfalfa. Inspection of individual fields suggested EPN populations established in prior years at the residual soil core level of 18-35% can respond positively to an increase of susceptible hosts in both alfalfa and corn, often increasing their presence to 100%.

Genetic Structure of Atmospheric Populations of Gibberella zeae.

ABSTRACT Gibberella zeae, causal agent of Fusarium head blight (FHB) of wheat and barley and Gibberella ear rot (GER) of corn, may be transported over long distances in the atmosphere. Epidemics of FHB and GER may be initiated by regional atmospheric sources of inoculum of G. zeae; however, little is known about the origin of inoculum for these epidemics. We tested the hypothesis that atmospheric populations of G. zeae are genetically diverse by determining the genetic structure of New York atmospheric populations (NYAPs) of G. zeae, and comparing them with populations of G. zeae collected from seven different states in the northern United States. Viable, airborne spores of G. zeae were collected in rotational (lacking any apparent within-field inoculum sources of G. zeae) wheat and corn fields in Aurora, NY in May through August over 3 years (2002 to 2004). We evaluated 23 amplified fragment length polymorphism (AFLP) loci in 780 isolates of G. zeae. Normalized genotypic diversity was high (ranging from 0.91 to 1.0) in NYAPs of G. zeae, and nearly all of the isolates in each of the populations represented unique AFLP haplotypes. Pairwise calculations of Nei's unbiased genetic identity were uniformly high (>0.99) for all of the possible NYAP comparisons. Although the NYAPs were genotypically diverse, they were genetically similar and potentially part of a large, interbreeding population of G. zeae in North America. Estimates of the fixation index (G(ST)) and the effective migration rate (Nm) for the NYAPs indicated significant genetic exchange among populations. Relatively low levels of linkage disequilibrium in the NYAPs suggest that outcrossing is common and that the populations are not a result of a recent bottleneck or invasion. When NYAPs were compared with those collected across the United States, the observed genetic identities between the populations ranged from 0.92 to 0.99. However, there was a significant negative correlation (R = -0.59, P < 0.001) between genetic identity and geographic distance, suggesting that some genetic isolation may occur on a continental scale. The contribution of long-distance transport of G. zeae to regional epidemics of FHB and GER remains unclear, but the diverse atmospheric populations of G. zeae suggest that inoculum may originate from multiple locations over large geographic distances. Practically, the long-distance transport of G. zeae suggests that management of inoculum sources on a local scale, unless performed over extensive production areas, will not be completely effective for the management of FHB and GER.

Estimating the potato leafhopper Empoasca fabae (Homoptera: Cicadellidae) overwintering range and spring premigrant development by using geographic information system.

The potato leafhopper, Empoasca fabae (Harris), is a circular migratory pest of many crops in the United States that overwinters in the southern states. Northward migrant population arrival to the northern states occurs earlier in the north central states compared with northeastern states. Migrant leafhopper arrival to the north varies from year to year depending on factors influencing the development of spring migrants in the overwintering areas and on timing of weather systems capable of transporting the migrants northward. An estimate of the potato leafhopper minimum temperature survival, the geographic limits of the potato leafhopper overwintering range, leafhopper spring development in the overwintering areas, and the identification of the spring migration initiation northwards can help to predict the leafhopper arrival time in the northern states. In the current study, geographic information system (GIS) was used to estimate the potato leafhopper minimum temperature survival and premigrant development. The minimum winter temperature was estimated by overlaying minimum temperature isolines with potato leafhopper collection data taken during the winter, The geographic limits of the overwintering range were estimated using the minimum temperature survival to create a condition-based model by using ArcMap-GIS 8.2. The estimated overwintering range was larger and covered areas further north than previously estimated and included Missouri, Kansas, Kentucky, Virginia, and Maryland. The use of degree-day accumulation to estimate days of first adult emergence in the overwintering areas resulted in earliest adult emergence in the south central region. First adult emergence in south central and southeastern areas occurred before the detection of potato leafhoppers in the north central United States. These data suggested that the difference in population arrival between the north central states and the northeastern states was more dependent on factors affecting the migration and weather conditions encountered along the migration pathway.

Transect sampling to enhance efficiency of corn rootworm (Coleoptera: Chrysomelidae) monitoring in corn.

Crop monitoring for adult corn rootworms, Diabrotica virgifera virgifera LeConte and Diabrotica barberi Smith and Lawrence, remains the best means to assess fields at risk from this pest if replanted to corn, Zea mays (L.). Improvements in sampling methodology, including the development of a sequential sampling plan, have reduced the minimum sampling time required to make a management decision to 20 min or less per field per visit. However, many growers and crop consultants still find this time commitment a constraint to repeated scouting. A common currently used sampling method involves systematically covering most of the field following a "W" pattern. The feasibility of replacing the current sampling pattern with a simpler and less time-consuming transect (straight line) pattern was assessed. When sampling methods were compared, computer simulations demonstrated that treatment decisions based on transect sampling would have an acceptably low error rate averaging 10% over a range of realistic corn rootworm densities (0-2 adults per plant). This error rate represented a decrease in accuracy of <1% compared with systematic sampling. Field trials using transect, systematic, and random sampling in each field were used to compare the categorization of adult corn rootworm densities into "above" or "below" threshold with a sequential sampling plan. Efficiency measured in time to reach a decision, number of corn plants evaluated, and time divided by plants observed were compared between sampling methods. The three methods did not differ significantly in the number of plants evaluated or in the categorization of corn rootworm populations. Transect sampling resulted in a significantly shorter time divided by plants observed (38 s), than either systematic (78 s), or random sampling methods (166 s). Based on these results transect sampling reduces sampling time 51% compared with systematic sampling and thus could be used to reduce total sampling times substantially.

Conducting public-sector research on commercialized transgenic seed: in search of a paradigm that works.

Public-sector scientists have a mandate to independently evaluate agricultural products available to American farmers on the open market, whereas the companies that sell the products must protect their intellectual property.  However, as a consequence of the latter concern, public scientists currently are prohibited by industry-imposed restrictions from conducting research on commercialized transgenic seed without permission of the company.  Industry acknowledged the seriousness of the problem after public warnings by a large group of entomologists to EPA and scientific advisory panels that the assumption of independence of public-sector studies on these products is no longer valid under current restrictions.  Both industry and public scientists are working to find an amicable, mutually-acceptable solution.  Recently, the American Seed Trade Association brokered a draft set of principles designed to protect the legitimate property rights of companies while allowing public scientists independence to conduct most types of research on their commercialized products without the need for case-by-case agreements.  While there are a number of potential pitfalls in implementation of the principles across companies, this effort represents a major step forward, and there is reason for optimism that this approach can be made to work to the benefit of industry, public scientists, and the American public.