European corn borer (ECB, Ostrinia nubilalis Hübner) and corn earworm (CEW, Helicoverpa zea Boddie) are important yield‐reducing insect pests of field corn ( Zea mays L. var. indentata ) in the northeastern United States. Transgenic hybrids bioengineered to express insecticidal proteins from the bacterium Bacillus thuringiensis (Bt) have revolutionized methods to control these caterpillars and other insect pests in corn. However, corn producers are faced with two decision‐making challenges every year: selection of the most appropriate Bt hybrids for the targeted pest complex from a large list of commercially available hybrids, and finding competitively yielding conventional hybrids for the required refuge hectare. This study was conducted at five sites across Maryland for 3 yr to evaluate more than 100 hybrids representing six Bt trait groups (three single‐protein and three multi‐protein genes) and a conventional non‐Bt group for their relative susceptibility to lepidopteran feeding injury and yield performance. Conventional hybrid tolerance to ECB injury or CEW ear damage and their yield varied each year except Dekalb DKC61‐22, which consistently produced greater yield than other non‐Bt hybrids. Injury caused by ECB was not found among any of the Bt hybrid groups. Hybrids with multi‐protein Bt traits showed greater ear protection than those with single‐protein Bt traits, but this improvement was small. Genuity VT3 Pro and Agrisure Viptera 3111 hybrids had the best ear protection and yield performance among the six tested Bt traits.
Significance Area-wide Bacillus thuringiensis (Bt) adoption suppresses pests regionally, with declines expanding beyond the planted Bt crops into other non-Bt crop fields. The offsite benefits to vegetable crops from such pest suppression have not been documented. We show that widespread Bt field corn adoption is strongly associated with marked decreases in the number of recommended insecticidal applications, insecticides applied, and damage to vegetable crops in the United States. These positive impacts to growers, including organic producers, in the agricultural landscape expands on known ecological effects of Bt adoption.
A nutrient-based feeding stimulant and a diaminostilbene disulfonic acid-derived enhancer (fluorescent brightener, Blankophor BBH®; Burlington Chemical, Burlington, NC) were evaluated as adjuvants for the nuclear polyhedrosis virus of the celery looper, Anagrapha falcifera (Kirby) (AfMNPV), against the beet armyworm, Spodoptera exigua (Hübner), on collard, Brassica oleracea L. (Acephala group), cv. ‘Vates’. Tests included holding larvae on sprayed potted plants in the laboratory and bioassays of foliage collected from sprayed plants in the field. The feeding stimulant increased virus-caused mortality in all tests. The enhancer increased virus-caused mortality in the bioassays of field-collected foliage but not in the test of potted plants. Treatments with both materials maintained the greatest levels of activity over time in the field. At the concentration tested on potted plants (up to 0.5% of the spray), the enhancer may have acted as a feeding deterrent. Therefore, on the whole plants, where the larvae were free to move around, effects on feeding behavior may have reduced the effectiveness of the enhancer. In the bioassay of field-collected foliage, larvae were confined on small pieces of foliage and, thus, did not have the option of moving away from the enhancer. Because the enhancer and the feeding stimulant have both been previously reported to also protect viruses from degradation by ultraviolet light, exposure to sunlight in the field could also have contributed to differences in larval mortality.
INTRODUCTION Recent advances in molecular biology and genetics have led to the creation of exciting new opportunities in the field of agriculture. Some of the first and most widely-used genetically-engineered crops have been modified to express insecticidal crystalline (Cry) proteins derived from the bacterium Bacillus thuringiensis (Bt). These so-called Bt crops are protected from the feeding of various groups of herbivorous pest insects. In 1995 and 1996, varieties of potato, cotton and com expressing various Bt proteins were approved for commercial use in the United States. In Bt potato, the Cry3Aa protein provides protection against damage from the Colorado potato beetle. In Bt cotton and Bt com, the proteins expressed (CrylAc in cotton and CrylAb or CrylF in com) confer protection against a number of lepidopteran herbivores. The Bt cotton and Bt com products, in particular, are widely used (James, 2001). Bt cotton has since been registered for commercial use in Argentina, Australia, China, Columbia, India, Indonesia, Mexico, and South Africa. Bt com has a similar potential; in 2001, about 20 million acres of Bt com were planted in the United States, almost 40% of com acres in Argentina are occupied with Bt com, and smaller amounts were planted commercially in Canada, Spain, and South Africa. A critical part of the introduction of such products is to ensure their environmental safety. In this chapter, weshall describe the safety assessment process used to evaluate the potential impact of Bt crops on non-target species, and we review the laboratory and field research that has been conducted in this area (see also Shelton et al., 2002 for a broader review of the impacts of Bt crops).
One of the possible adverse effects of transgenic insecticidal crops is the unintended decline in the abundance of nontarget arthropods. Field trials designed to evaluate potential nontarget effects can be more complex than expected because decisions to conduct field trials and the selection of taxa to include are not always guided by the results of laboratory tests. Also, recent studies emphasize the potential for indirect effects (adverse impacts to nontarget arthropods without feeding directly on plant tissues), which are difficult to predict because of interactions among nontarget arthropods, target pests, and transgenic crops. As a consequence, field studies may attempt to monitor expansive lists of arthropod taxa, making the design of such broad studies more difficult and reducing the likelihood of detecting any negative effects that might be present. To improve the taxonomic focus and statistical rigor of future studies, existing field data and corresponding power analysis may provide useful guidance. Analysis of control data from several nontarget field trials using repeated-measures designs suggests that while detection of small effects may require considerable increases in replication, there are taxa from different ecological roles that are sampled effectively using standard methods. The use of statistical power to guide selection of taxa for nontarget trials reflects scientists’ inability to predict the complex interactions among arthropod taxa, particularly when laboratory trials fail to provide guidance on which groups are more likely to be affected. However, scientists still may exercise judgment, including taxa that are not included in or supported by power analyses.
Overwintering success is an important determinant of arthropod populations that must be considered as climate change continues to influence the spatiotemporal population dynamics of agricultural pests. Using a long-term monitoring database and biologically relevant overwintering zones, we modeled the annual and seasonal population dynamics of a common pest, Helicoverpa zea (Boddie), based on three overwintering suitability zones throughout North America using four decades of soil temperatures: the southern range (able to persist through winter), transitional zone (uncertain overwintering survivorship), and northern limits (unable to survive winter). Our model indicates H. zea population dynamics are hierarchically structured with continental-level effects that are partitioned into three geographic zones. Seasonal populations were initially detected in the southern range, where they experienced multiple large population peaks. All three zones experienced a final peak between late July (southern range) and mid-August to mid-September (transitional zone and northern limits). The southern range expanded by 3% since 1981 and is projected to increase by twofold by 2099 but the areas of other zones are expected to decrease in the future. These changes suggest larger populations may persist at higher latitudes in the future due to reduced low-temperature lethal events during winter. Because H. zea is a highly migratory pest, predicting when populations accumulate in one region can inform synchronous or lagged population development in other regions. We show the value of combining long-term datasets, remotely sensed data, and laboratory findings to inform forecasting of insect pests.
Introduced hornets increase natural enemies and stress factors detrimental to honey bees, Apis mellifera L. Hornets are slightly bigger than honey bee drones, the largest member of A. mellifera colonies, offering a possibility of excluding hornets from entering hives because of their larger size. Using screen with an appropriate size of holes allowed free flow of honey bees and may impede the passage of larger predators, including hornets. Metal screens with 0.74 cm holes were installed in eight honey bee hives, using eight colonies without screens for comparison. Colonies with screens produced significantly more honey than did colonies without screens, and no differences were found in the accumulation of pollen or presence of brood between colonies with or without screens. Results indicated the screens were not detrimental to reproduction and honey production by the colonies, but had a beneficial side effect on colony fitness, probably my reducing robbing. Vespa crabro from preserved museum specimens were as small as 0.64 cm at its widest dimension, V. velutina 0.70 cm, while V. mandarinia might not pass through a screen hole smaller than 1.1 cm. Honey bee drones had a maximum metathorax width of 0.6 cm, suggesting that mesh with a hole size slightly larger than 0.60 cm might be appropriate to exclude these hornet species without decreasing productive and reproductive parameters of honey bee colonies.
Objectives Assessment and identification of spatial structures in the distribution and abundance of invasive species is important for unraveling the underlying ecological processes. The invasive agricultural insect pest Halyomorpha halys that causes severe economic losses in the United States is currently expanding both within United States and across Europe. We examined the drivers of H. halys invasion by characterizing the distribution and abundance patterns of H. halys and native stink bugs (Chinavia hilaris and Euschistus servus) across eight different spatial scales. We then quantified the interactive and individual influences of temperature, and measures of resource availability and distance from source populations, and their relevant spatial scales. We used Moran's Eigenvector Maps based on Gabriel graph framework to quantify spatial relationships among the soybean fields in mid-Atlantic Unites States surveyed for stink bugs. Findings Results from the multi-spatial scale, multivariate analyses showed that temperature and its interaction with resource availability and distance from source populations structures the patterns in H. halys at very broad spatial scale. H. halys abundance decreased with increasing average June temperature and distance from source population. H. halys were not recorded at fields with average June temperature higher than 23.5°C. In parts with suitable climate, high H. halys abundance was positively associated with percentage developed open area and percentage deciduous forests at 250m scale. Broad scale patterns in native stink bugs were positively associated with increasing forest cover and, in contrast to the invasive H. halys, increasing mean July temperature. Our results identify the contrasting role of temperature in structuring regional patterns in H. halys and native stink bugs, while demonstrating its interaction with resource availability and distance from source populations for structuring H. halys patterns. Conclusion These results help predicting the pest potential of H. halys and vulnerability of agricultural systems at various regions, given the climatic conditions, and its interaction with resource availability and distance from source populations. Monitoring and control efforts within parts of the United States and Europe with more suitable climate could focus in areas of peri-urban developments with deciduous forests and other host plants, along with efforts to reduce propagule pressure.
Egg masses were placed on snap beans at 7, 14, 21, and 28 days before harvest to determine the nature and distribution of feeding injury by Ostrinia nubilalis (Hübner). Early instars fed first on leaves and then bored into stems and pods as they reached the late 2nd and 3rd instars. About 37% of the stem damage occurred inside the lower portion of the main stem, with the remaining damage distributed among lateral stems. Second and later instars invaded all sizes of pods with a significant preference toward the marketable pods (sieve sizes 3-6). External symptoms, indicating that the pods had been damaged, were not consistently observed. Many marketable pods were completely normal in appearance despite extensive boring, and the only sign of injury was the entry hole. Injury to pin pods (sieve sizes 0-2) invariably was associated with external symptoms, and it is unlikely that these pods will develop to a marketable size. The nature and distribution of feeding injury to pods and stems depended on time of oviposition. When hatching occurred at bloom, ca. half of the surviving larvae invaded pods of all sizes and caused little external evidence of injury by harvest time. When hatching occurred one week or more before bloom, surviving larvae bored primarily into lateral stems; however, ca. 1/3 of these larvae shifted their feeding activity to pods as they became available.
