Norman C. Elliott

Bio: Norman C. Elliott is an academic researcher from Agricultural Research Service. The author has contributed to research in topics: Aphid & Aphididae. The author has an hindex of 25, co-authored 80 publications receiving 1950 citations. Previous affiliations of Norman C. Elliott include Oklahoma State University–Stillwater & Oregon State University.

Effects of an invading coccinellid on native coccinellids in an agricultural landscape.

Abstract: Seven native coccinellid species inhabited alfalfa, corn, and small grain fields in eastern South Dakota prior to invasion and establishment of Coccinella septempunctata L. Six species occurred in all crops, however, Adalia bipunctata (L.) occurred only in corn. The structure of native coccinellid communities differed significantly for years prior to compared with years after establishment of C. septempunctata in fields of the three agricultural crops. Differences in community structure were accounted for mainly by reduced abundance of two species, C. transversoguttata richardsoni Brown and Adalia bipunctata (L.). Annual abundance of C. transversoguttata richardsoni averaged 20-32 times lower during post-invasion years than in years prior to invasion, depending on crop; while annual abundance of A. bipunctata averaged 20 times lower in corn after invasion. Addition of C. septempunctata to the community did not result in a significant increase in total abundance of coccinellids in the crops. Coccinellid abundance in agricultural crops may be limited by the total abundance of prey or by the availability of other requisites in the landscape as a whole. Therefore, introduction of a new species, while resulting in reductions in native species populations, may not increase total coccinellid abundance, and may therefore have no net effect on biological control of aphid pests.

Influence of within-field and landscape factors on aphid predator populations in wheat

Abstract: The influence of prey density, within-field vegetation, and the composition and patchiness of the surrounding landscape on the abundance of insect predators of cereal aphids was studied in wheat fields in eastern South Dakota, USA. Cereal aphids, aphid predators, and within-field vegetation were sampled in 104 fields over a three year period (1988–1990). The composition and patchiness of the landscape surrounding each field were determined from high altitude aerial photographs. Five landscape variables, aggregated at three spatial scales ranging from 2.6 km2 to 581 km2, were measured from aerial photographs. Regression models incorporating within-field and landscape variables accounted for 27–49% of the variance in aphid predator abundance in wheat fields. Aphid predator species richness and species diversity were also related to within-field and landscape variables. Some predators were strongly influenced by variability in the composition and patchiness of the landscape surrounding a field at a particular spatial scale while others responded to variability at all scales. Overall, predator abundance, species richness, and species diversity increased with increasing vegetational diversity in wheat fields and with increasing amounts of non-cultivated lands and increasing patchiness in the surrounding landscape.

Changes in Chlorophyll a Fluorescence Induction Kinetics in Cereals Infested with Russian Wheat Aphid (Homopetra: Aphididea)

Abstract: Plant entries that previously had tested resistant or susceptible to Russian wheat aphid, Diuraphis noxia (Mordvilko), were used to evaluate the effect of aphid feeding on leaf chlorophyll content and in vivo chlorophyll fluorescence induction kinetics. D. noxia feeding for 96 h caused significant reductions in chlorophyll a, chlorophyll b, and total chlorophyll content in susceptible wheat (‘Avon’, ‘TAM W-101’) and barley (‘Wintermalt’). Total chlorophyll content and constituent chlorophyll a and b levels were not significantly affected by D. noxia in resistant wheat (PI 366616, PI 372129) or barley (PI 366450) and in neither resistant (PI 386156) nor susceptible (‘Beagle 82’) critical. D. noxia infestation resulted in significant alterations of the primary fluorescence induction transients. When compared with non infested control plants, infested susceptible wheat and barley showed significantly increased non variable fluorescence (F) and decreased maximal fluorescence ( Fm ) and variable fluorescence ( Fv ). In contrast, values for these parameters did not differ significantly among the infested and non infested controls of resistant plants. When compared with control plants, the photochemical efficiency of photo system II ( F/Fm ) and the half-rise time from Fo to Fm (t1/2) were reduced significantly in the infested susceptible entries but remained relatively unchanged for the infested resistant cultivates. No significant differences between infested and non infested plants were observed in the measured chlorophyll fluorescence parameters for either the resistant or the susceptible critical, which implied a much different resistance mechanism(s) to D. noxia The results of this investigation suggest that D. noxia damage goes beyond the simple removal of photosyntheses from the plant. The substantial decrease in F/Fm following aphid infestation for the susceptible wheat and barley indicated a significant decrease in the capacity and efficiency of the primary photochemistry of photo system II.

Temperature-Dependent Development of Immature Stages of the Western Corn Rootworm, Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae)

Abstract: Larval and pupal development of western corn rootworm was studied at eight constant temperatures ranging from 15 to 33°C. Development from hatch to adult stage occurred at 15–31.5°C; no larvae completed the second stage at 33°C. Adult survival decreased and wing deformities increased significantly at 15 and 31.5°C. Optimum development and survival occurred within the temperature range of 21–30°C. Males developed faster than females in all stages at temperatures from 18–30°C, but the sexes have a similar lower thermal threshold of development estimated to be near 9°C. The relationship between developmental rate and temperature was described for both sexes in all stages using linear and nonlinear equations. The information presented will facilitate the development of phenological models for this important pest species.

Coccinellid Introductions: Potential for and Evaluation of Nontarget Effects

Abstract: Aphid-feeding Coccinellidae, subfamily Coccinellinae, are found in many terrestrial habitats and have been used extensively for biological control of aphid pest species (Hagen 1962, 1974; Frazer 1988; Hodek and Honek 1996; Obrycki and Kring 1998). Most if not all aphidophagous Coccinellidae feed on several prey items (Hodek 1993, Hodek and Honek 1996); the question is what level of prey specificity is required for the safe introduction of these predators? The selection of coccinellid species for importation is typically based on field observations of predation on the target pest and/or consistent associations of the coccinellid and prey species in their native range. While these observations are a logical first step, observed predation does not necessarily mean that the prey is preferred or suitable for development and reproduction (Strand and Obrycki 1996, Obrycki et al. 1997a).

Defaunation in the Anthropocene

Abstract: We live amid a global wave of anthropogenically driven biodiversity loss: species and population extirpations and, critically, declines in local species abundance. Particularly, human impacts on animal biodiversity are an under-recognized form of global environmental change. Among terrestrial vertebrates, 322 species have become extinct since 1500, and populations of the remaining species show 25% average decline in abundance. Invertebrate patterns are equally dire: 67% of monitored populations show 45% mean abundance decline. Such animal declines will cascade onto ecosystem functioning and human well-being. Much remains unknown about this “Anthropocene defaunation”; these knowledge gaps hinder our capacity to predict and limit defaunation impacts. Clearly, however, defaunation is both a pervasive component of the planet’s sixth mass extinction and also a major driver of global ecological change.

Ecosystem services and agriculture: tradeoffs and synergies.

Abstract: Agricultural ecosystems provide humans with food, forage, bioenergy and pharmaceuticals and are essential to human wellbeing. These systems rely on ecosystem services provided by natural ecosystems, including pollination, biological pest control, maintenance of soil structure and fertility, nutrient cycling and hydrological services. Preliminary assessments indicate that the value of these ecosystem services to agriculture is enormous and often underappreciated. Agroecosystems also produce a variety of ecosystem services, such as regulation of soil and water quality, carbon sequestration, support for biodiversity and cultural services. Depending on management practices, agriculture can also be the source of numerous disservices, including loss of wildlife habitat, nutrient runoff, sedimentation of waterways, greenhouse gas emissions, and pesticide poisoning of humans and non-target species. The tradeoffs that may occur between provisioning services and other ecosystem services and disservices should be evaluated in terms of spatial scale, temporal scale and reversibility. As more effective methods for valuing ecosystem services become available, the potential for ‘win–win’ scenarios increases. Under all scenarios, appropriate agricultural management practices are critical to realizing the benefits of ecosystem services and reducing disservices from agricultural activities.

Sustainable pest regulation in agricultural landscapes: a review on landscape composition, biodiversity and natural pest control

Abstract: Agricultural intensification has resulted in a simplification of agricultural landscapes by the expansion of agricultural land, enlargement of field size and removal of non-crop habitat. These changes are considered to be an important cause of the rapid decline in farmland biodiversity, with the remaining biodiversity concentrated in field edges and non-crop habitats. The simplification of landscape composition and the decline of biodiversity may affect the functioning of natural pest control because non-crop habitats provide requisites for a broad spectrum of natural enemies, and the exchange of natural enemies between crop and non-crop habitats is likely to be diminished in landscapes dominated by arable cropland. In this review, we test the hypothesis that natural pest control is enhanced in complex patchy landscapes with a high proportion of non-crop habitats as compared to simple large-scale landscapes with little associated non-crop habitat. In 74% and 45% of the studies reviewed, respectively, natural enemy populations were higher and pest pressure lower in complex landscapes versus simple landscapes. Landscape-driven pest suppression may result in lower crop injury, although this has rarely been documented. Enhanced natural enemy activity was associated with herbaceous habitats in 80% of the cases (e.g. fallows, field margins), and somewhat less often with wooded habitats (71%) and landscape patchiness (70%). The similar contributions of these landscape factors suggest that all are equally important in enhancing natural enemy populations. We conclude that diversified landscapes hold most potential for the conservation of biodiversity and sustaining the pest control function.

Can generalist predators be effective biocontrol agents

Abstract: Theoretical developments are helping us to comprehend the basic parameters governing the dynamics of the interactions between generalist predators and their many pest and nonpest prey. In practice, however, inter- and intraspecific interactions between generalist predators, and between the predators and their prey, within multispecies systems under the influence of rapidly changing biotic and abiotic variables are difficult to predict. We discuss trade-offs between the relative merits of specialists and generalists that allow both to be effective, and often complementary, under different circumstances. A review of manipulative field studies showed that in approximately 75% of cases, generalist predators, whether single species or species assemblages, reduced pest numbers significantly. Techniques for manipulating predator numbers to enhance pest control at different scales are discussed. We now need to find ways of disentangling the factors influencing positive and negative interactions within natural enemy communities in order to optimize beneficial synergies leading to pest control.

REVIEW: An overview of the environmental risks posed by neonicotinoid insecticides

Abstract: Summary 1. Neonicotinoids are now the most widely used insecticides in the world. They act systemically, travelling through plant tissues and protecting all parts of the crop, and are widely applied as seed dressings. As neurotoxins with high toxicity to most arthropods, they provide effective pest control and have numerous uses in arable farming and horticulture. 2. However, the prophylactic use of broad-spectrum pesticides goes against the long-established principles of integrated pest management (IPM), leading to environmental concerns. 3. It has recently emerged that neonicotinoids can persist and accumulate in soils. They are water soluble and prone to leaching into waterways. Being systemic, they are found in nectar and pollen of treated crops. Reported levels in soils, waterways, field margin plants and floral resources overlap substantially with concentrations that are sufficient to control pests in crops, and commonly exceed the LC50 (the concentration which kills 50% of individuals) for beneficial organisms. Concentrations in nectar and pollen in crops are sufficient to impact substantially on colony reproduction in bumblebees. 4. Although vertebrates are less susceptible than arthropods, consumption of small numbers of dressed seeds offers a route to direct mortality in birds and mammals. 5. Synthesis and applications. Major knowledge gaps remain, but current use of neonicotinoids is likely to be impacting on a broad range of non-target taxa including pollinators and soil and aquatic invertebrates and hence threatens a range of ecosystem services.