Abstract
We present a method for calculating the Acute Insecticide Toxicity Loading (AITL) on US agricultural lands and surrounding areas and an assessment of the changes in AITL from 1992 through 2014. The AITL method accounts for the total mass of insecticides used in the US, acute toxicity to insects using honey bee contact and oral LD50 as reference values for arthropod toxicity, and the environmental persistence of the pesticides. This screening analysis shows that the types of synthetic insecticides applied to agricultural lands have fundamentally shifted over the last two decades from predominantly organophosphorus and N-methyl carbamate pesticides to a mix dominated by neonicotinoids and pyrethroids. The neonicotinoids are generally applied to US agricultural land at lower application rates per acre; however, they are considerably more toxic to insects and generally persist longer in the environment. We found a 48- and 4-fold increase in AITL from 1992 to 2014 for oral and contact toxicity, respectively. Neonicotinoids are primarily responsible for this increase, representing between 61 to nearly 99 percent of the total toxicity loading in 2014. The crops most responsible for the increase in AITL are corn and soybeans, with particularly large increases in relative soybean contributions to AITL between 2010 and 2014. Oral exposures are of potentially greater concern because of the relatively higher toxicity (low LD50s) and greater likelihood of exposure from residues in pollen, nectar, guttation water, and other environmental media. Using AITL to assess oral toxicity by class of pesticide, the neonicotinoids accounted for nearly 92 percent of total AITL from 1992 to 2014. Chlorpyrifos, the fifth most widely used insecticide during this time contributed just 1.4 percent of total AITL based on oral LD50s. Although we use some simplifying assumptions, our screening analysis demonstrates an increase in pesticide toxicity loading over the past 26 years, which potentially threatens the health of honey bees and other pollinators and may contribute to declines in beneficial insect populations as well as insectivorous birds and other insect consumers.
Highlights
Insects form the basis of the food web that sustains life on Earth
We propose that the Acute Insecticide Toxicity Loading (AITL) could be used as a screening tool by providing year-to-year comparison of toxicity loading over time, measuring change in the potential toxicity of chemicals released into the environment, predicting potential impacts of new insecticides being considered for registration, and for surveying insecticide use and impacts on agricultural land
A comparison of AITLs calculated for different pesticide groupings demonstrates that insecticides contribute nearly 100 percent of the acute toxicity loading on honey bees and other beneficial insects of pesticides applied to agricultural land and surrounding areas in the US compared to herbicides, fungicides, and others
Summary
Insects form the basis of the food web that sustains life on Earth. They are critical to ecosystem success, providing food for amphibians, fish, birds, reptiles, and mammals. Insects contribute to the agricultural production of crops that feed humankind, both as the primary pollinators of many plants and as natural controls of pest insects that feed on crops important to human survival. A diverse population of insects benefits agriculture by keeping a balance between predatory and pest insects and providing pollination services [1]. With conventional farming practices relying primarily on chemical insecticides for pest insect management, ecosystems comprising US agricultural lands are highly impacted through both direct effects on insects and direct and indirect effects on other species [3]. Many members of the ecosystem may not be exposed to sufficient doses of insecticides to suffer acutely lethal poisonings, sublethal and indirect adverse effects have been demonstrated to occur [4]
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