Robert K. D. Peterson

Risk assessments for the insect repellents DEET and picaridin

For the use of topical insect repellents, DEET and picaridin, human health risk assessments were conducted for various population subgroups. Acute, subchronic, and chronic dermal exposures were examined. No-observed-effect-levels (NOELs) of 200, 300, and 100mg/kg body weight (BW) were used as endpoints for DEET for acute, subchronic, and chronic exposures, respectively. For picaridin, a NOEL of 2000 mg/kg BW/day for acute exposure and a NOEL of 200 mg/kg BW/day for subchronic and chronic exposures were used. Daily exposures to several population subgroups were estimated. Risks were characterized using the Margin of Exposure (MOE) method (NOEL divided by the estimated exposure), whereby estimated MOEs were compared to an MOE of 100. Estimates of daily exposures ranged from 2 to 59 mg/kg BW/day for DEET and 2 to 22 mg/kg BW/day for picaridin. Children had the lowest MOEs. However, none of the estimated exposures exceeded NOELs for either repellent. At 40% DEET for acute exposure, children < or = 12 years had MOEs below 100. For subchronic and chronic exposures children at > or = 25% DEET and at 15% picaridin had MOEs below 100. Therefore, we found no significant toxicological risks from typical usage of these topical insect repellents.

A human-health risk assessment for West Nile virus and insecticides used in mosquito management.

West Nile virus (WNV) has been a major public health concern in North America since 1999, when the first outbreak in the Western Hemisphere occurred in New York City. As a result of this ongoing disease outbreak, management of mosquitoes that vector WNV throughout the United States and Canada has necessitated using insecticides in areas where they traditionally have not been used or have been used less frequently. This has resulted in concerns by the public about the risks from insecticide use. The objective of this study was to use reasonable worst-case risk assessment methodologies to evaluate human-health risks for WNV and the insecticides most commonly used to control adult mosquitoes. We evaluated documented health effects from WNV infection and determined potential population risks based on reported frequencies. We determined potential acute (1-day) and subchronic (90-day) multiroute residential exposures from each insecticide for several human subgroups during a WNV disease outbreak scenario. We then compared potential insecticide exposures to toxicologic and regulatory effect levels. Risk quotients (RQs, the ratio of exposure to toxicologic effect) were < 1.0 for all subgroups. Acute RQs ranged from 0.0004 to 0.4726, and subchronic RQs ranged from 0.00014 to 0.2074. Results from our risk assessment and the current weight of scientific evidence indicate that human-health risks from residential exposure to mosquito insecticides are low and are not likely to exceed levels of concern. Further, our results indicate that, based on human-health criteria, the risks from WNV exceed the risks from exposure to mosquito insecticides.

Biotic stress and yield loss.

Preface Robert K.D. Peterson and Leon G. Higley Illuminating the Black Box: The Relationship Between Injury and Yield Robert K.D. Peterson and Leon G. Higley Yield Loss and Insect Management Leon G. Higley Techniques for Evaluating Yield Loss from Insects G. David Buntin Yield Loss of Field Corn from Insects Michael D. Culy Phenological Disruption and Yield Loss from Insects Scott H. Hutchins Photosynthesis, Yield Loss, and Injury Guilds Robert K.D. Peterson The Influence of Cultivar and Plant Architecture on Yield Loss Fikru J. Haile Drought Stress, Insects, and Yield Loss Fikru J. Haile The Impact of Herbivory on Plants: Yield, Fitness, and Population Dynamics Kevin J. Delaney and Tulio B. Macedo Contrasting Plant Responses to Herbivory in Wild and Domesticated Habitats Stephen C. Welter Crop Disease and Yield Loss Brian D. Olson Quantifying Crop Yield Response to Weed Populations: Applications and Limitations John L. Lindquist and Stevan Z. Knezevic Mechanisms of Crop Loss Due to Weed Competition John L. Lindquist Index

A Screening Level Approach for Nontarget Insect Risk Assessment: Transgenic Bt Corn Pollen and the Monarch Butterfly (Lepidoptera: Danaidae)

Abstract Quantitative risk assessment affords an objective approach for assessing ecological risk from crops produced using biotechnology. Ecological risk assessment for plant-incorporated insecticidal proteins necessitates consideration of risks to nontarget insects when species-specific hazard information may be lacking. Screening-level risk assessment methods afford a means by which risks to species of concern may be evaluated conservatively using exposure estimates, host-range information, and a probabilistic estimate of toxicity to sensitive species. This approach was applied to the special case of Bt corn pollen risk to monarch butterfly, Danaus plexippus (L.), populations; the results were compared with more highly refined risk assessment techniques in terms of the risk conclusions which can be developed with more highly certain information. Exposure analysis based on readily available literature showed pollen interception by the host for monarch butterfly larvae (common milkweed, Asclepias syriaca L.) declined exponentially with distance from the pollen source. Intra- and inter-genera sensitivity of lepidopteran species was used to project effect to monarch butterfly larvae. When the 90th percentile of effect (LC50) was used to estimate monarch butterfly sensitivity to Bt corn pollen expressing Cry1A(b) protein, the risk of lethality to individual larvae was negligible at >1 m from the edge of source corn fields. Subsequent field measurements of pollen distribution, interception by milkweed, and especially effects determinations for monarch butterfly larvae exposed to Cry1A(b) toxin indicate that the screening-level approach was effective in focusing the scope of the problem to exposure from high-expressing Cry1A(b) events occurring within source cornfields or at the near-field edge. Screening level risk assessment conservatively identifies the scope of concern and the uncertainties that need clarification so that subsequent research can be appropriately focused.

TNT and 4-amino-2,6-dinitrotoluene influence on germination and early seedling development of tall fescue

Cost-effective and environmentally acceptable methods are needed to remediate munitions-contaminated soil. Some perennial grass species are tolerant of soil contaminants and may promote remediation because of their high water use and extensive fibrous root systems. The effects of 2,4,6-trinitrotoluene (TNT) and its reduction product, 4-amino-2,6-dinitrotoluene (4ADNT), on germination and early seedling development of tall fescue (Festuca arundinacea Schreb.) were determined. Tall fescue seeds were germinated in nutrient-free agar containing 0-60 mg TNT litre(-1) or 0-15 mg 4ADNT litre(-1). Germination decreased linearly as TNT concentration increased but was not significantly affected by 4ADNT at these concentrations. Concentrations less than 30 mg TNT litre(-1) or 7.5 mg 4ADNT litre(-1) had little effect on seedling growth and development. Higher TNT or 4ADNT concentrations substantially delayed seedling development, caused abnormal radicle tissue development, and reduced secondary root and shoot growth. Seedling respiration rates decreased linearly with increasing TNT concentration. Experiments indicate that tall fescue may be grown in soils that maintain soil solution concentrations of 30 mg TNT litre(-1) or less.

Risk analysis for plant-made vaccines

The production of vaccines in transgenic plants was first proposed in 1990 however no product has yet reached commercialization. There are several risks during the production and delivery stages of this technology, with potential impact on the environment and on human health. Risks to the environment include gene transfer and exposure to antigens or selectable marker proteins. Risks to human health include oral tolerance, allergenicity, inconsistent dosage, worker exposure and unintended exposure to antigens or selectable marker proteins in the food chain. These risks are controllable through appropriate regulatory measures at all stages of production and distribution of a potential plant-made vaccine. Successful use of this technology is highly dependant on stewardship and active risk management by the developers of this technology, and through quality standards for production, which will be set by regulatory agencies. Regulatory agencies can also negatively affect the future viability of this technology by requiring that all risks must be controlled, or by applying conventional regulations which are overly cumbersome for a plant production and oral delivery system. The value of new or replacement vaccines produced in plant cells and delivered orally must be considered alongside the probability and severity of potential risks in their production and use, and the cost of not deploying this technology – the risk of continuing with the status quo alternative.

Economic Cost Analysis of West Nile Virus Outbreak, Sacramento County, California, USA, 2005

Aerial spraying is cost-effective.

Wheat Stem Sawfly, Cephus cinctus Norton, Impact on Wheat Primary Metabolism: An Ecophysiological Approach

Abstract The impact of wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae), on the photosynthetic capacity and primary metabolism of wheat, Triticum aestivum L., was evaluated in three different environments: environmental growth chamber, greenhouse, and field. C. cinctus elicited different photosynthetic responses in different environments. Wheat gas exchange parameters, such as photosynthesis, stomatal conductance, intercellular CO2, and transpiration in the growth chamber environment were negatively affected by C. cinctus feeding. Conversely, the same gas exchange responses were not observed under greenhouse and field conditions. This study shows the important role of environmental variables, such as ambient CO2 concentrations and light intensity, on plant responses to herbivores.

A comparative ecological risk assessment for herbicides used on spring wheat: the effect of glyphosate when used within a glyphosate-tolerant wheat system

Abstract Glyphosate-tolerant spring wheat currently is being developed and most likely will be the first major genetically engineered crop to be marketed and grown in several areas of the northern Great Plains of the United States. The public has expressed concerns about environmental risks from glyphosate-tolerant wheat. Replacement of traditional herbicide active ingredients with glyphosate in a glyphosate-tolerant spring wheat system may alter ecological risks associated with weed management. The objective of this study was to use a Tier 1 quantitative risk assessment methodology to compare ecological risks for 16 herbicide active ingredients used in spring wheat. The herbicide active ingredients included 2,4-D, bromoxynil, clodinafop, clopyralid, dicamba, fenoxaprop, flucarbazone, glyphosate, MCPA, metsulfuron, thifensulfuron, tralkoxydim, triallate, triasulfuron, tribenuron, and trifluralin. We compared the relative risks of these herbicides to glyphosate to provide an indication of the effect of glyphosate when it is used in a glyphosate-tolerant spring wheat system. Ecological receptors and effects evaluated were avian (acute dietary risk), wild mammal (acute dietary risk), aquatic vertebrates (acute risk), aquatic invertebrates (acute risk), aquatic plants (acute risk), nontarget terrestrial plants (seedling emergence and vegetative vigor), and groundwater exposure. Ecological risks were assessed by integrating toxicity and exposure, primarily using the risk quotient method. Ecological risks for the 15 herbicides relative to glyphosate were highly variable. For risks to duckweed, green algae, groundwater, and nontarget plant seedling emergence, glyphosate had less relative risk than most other active ingredients. The differences in relative risks were most pronounced when glyphosate was compared with herbicides currently widely used on spring wheat. Nomenclature: Bromoxynil; clodinafop; clopyralid; dicamba; 2,4-dichlorophenoxy acetic acid; fenoxaprop; flucarbazone; glyphosate; MCPA; metsulfuron; spring wheat; thifensulfuron; tralkoxydim; triallate; triasulfuron; tribenuron; trifluralin; spring wheat, Triticum aestivum L.

Photosynthetic Responses of Legume Species to Leaf-Mass Consumption Injury

Abstract Several studies have addressed plant primary physiological responses (gas exchange responses) to insect herbivory. However, relatively few plant species have been examined. It is unknown whether responses to leaf-mass removal by insects vary among plant families and species. Within the legumes, only alfalfa, Medicago sativa L., and soybean, Glycine max (L.) Merrill, have been examined. The goal of this study was to test the hypothesis that gas exchange responses to leaf-mass consumption in a broad range of cultivated legumes do not differ from those of soybean and alfalfa. The species and cultivars used were M. sativa Cimarron, Medicago scutellata (L.) Sava, Medicago truncatula Gaertner Paraggio, Melilotus officinalis (L.) Pallas, Trifolium hybridum L., and Trifolium pratense L. Twelve greenhouse experiments were conducted and each legume species was used in a separate experiment. Depending on the experiment, there were either two or three treatments (control, simulated insect injury, and actual insect injury). For simulated and actual insect defoliation, injury was limited to a single leaf per plant. Simulated insect injury treatments were imposed by removing leaf tissue on each leaflet with scissors. For the actual insect defoliation treatment, fall armyworm larvae, Spodoptera frugiperda (J.E. Smith), were used. Defoliation of single leaves on the six species resulted in similar responses. Plant gas exchange variables (photosynthesis, stomatal conductance, intercellular CO2, and transpiration) were not significantly affected by either simulated or actual insect defoliation. Our results support the hypothesis that there is a generalized primary physiological response to leaf-mass consumption injury among the cultivated legumes. More generally, the results from this experiment support that there is a generalized plant gas exchange response to leaf-mass consumption injury.