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Mechanistic modeling of insecticide risks to breeding birds in North American agroecosystems
Etterson, M., K. Garber, AND E. Odenkirchen. Mechanistic modeling of insecticide risks to breeding birds in North American agroecosystems. PLoS ONE . Public Library of Science, San Francisco, CA, 12(5):e0176998, (2017).
This manuscript introduces the new integrated TIM/MCnest model. The model is applied to a risk assessment for 7 pesticides commonly used for corn in Midwestern agroecosystems. The intended audience is the general ecotoxicology community, risk assessors, and stakeholders for the interagency effort for pesticide risk assessment under Section 7 of the Endangered Species Act. We demonstrate clear differences among pesticides in population-level risk for birds. We also show how acute and chronic effects can be rationally combined in a single metric representing overall risk to breeding birds using confields and adjacent habitats.
Insecticide usage in the United States is ubiquitous in urban, suburban, and rural environments. In evaluating data for an insecticide registration application and for registration review, scientists at the United States Environmental Protection Agency (USEPA) assess the fate of the insecticide and the risk the insecticide poses to the environment and non-target wildlife. At the present time, current USEPA risk assessments do not include population-level endpoints. In this paper, we present a new mechanistic model, which allows risk assessors to estimate the effects of insecticide exposure on the survival and seasonal productivity of birds known to use agricultural fields during their breeding season. The new model was created from two existing USEPA avian risk assessment models, the Terrestrial Investigation Model (TIM v.3.0) and the Markov Chain Nest Productivity model (MCnest). The integrated TIM/MCnest model has been applied to assess the relative risk of 12 insecticides used to control corn pests on a suite of 31 avian species known to use cornfields in midwestern agroecosystems. The 12 insecticides that were assessed in this study are all used to treat major pests of corn (corn root worm borer, cutworm, and armyworm). After running the integrated TIM/MCnest model, we found extensive differences in risk to birds among insecticides, with chlorpyrifos and malathion (organophosphates) generally posing the greatest risk, and bifenthrin and ë-cyhalothrin (pyrethroids) posing the least risk. Comparative sensitivity analysis across the 31 species showed that life history parameters related to the timing of breeding and reproductive output per nest attempt offered the greatest explanatory power for predicting the magnitude of risk. An important advantage of TIM/MCnest is that it allows risk assessors to rationally combine both acute and chronic effects into a single unified measure of risk (percent reduction in annual fecundity). This unified measure of risk gives appropriate weights to acute effects versus chronic effects, both of which depend on the life history of the species rather than a priori levels of concern.