The cotton industry is feeling the sting after the EPA concluded that the use of a popular neonicotinoid insecticide in cotton poses a high risk to bees.
On Wednesday, the agency released its preliminary pollinator risk assessment for imidacloprid — the active ingredient in Bayer Crop Sciences’ Gaucho insecticide — as part of its registration review of the chemical. Imidacloprid is used by cotton producers to control the industry’s top two pests, thrips and tarnished plant bugs.
After examining the insecticide’s use in all crops, the EPA’s risk assessment concluded that bees are most at risk of exposure to damaging levels of the imidacloprid from foliar and seed treatments in cotton fields, a claim that both Bayer and some university scientists dispute. (Foliar applications in citrus fields were also rated high risk).
The conclusion could threaten the future registration of imidacloprid in cotton, which would leave cotton growers with higher costs, more insecticide use, and poorer control of pests, entomologists told DTN.
A DISPUTED CONCLUSION
In its assessment, EPA said it primarily considered bee exposure to imidacloprid through “direct contact by foliar spray of imidacloprid (i.e., interception of spray droplets either on or off the treated field) and oral ingestion (e.g., consumption of contaminated pollen and nectar)”.
The agency identified a threshold residue level for imidacloprid of 25 parts per billion (ppb), and concluded that residues in pollen or nectar above this level are likely to have a negative effect on pollinator hives, such as bee losses or reduced honey production.
“Data show that citrus and cotton may have residues of the pesticide in pollen and nectar above the threshold level,” the agency said in a press release. “Other crops such as corn and leafy vegetables either do not produce nectar or have residues below the EPA identified level.”
This conclusion surprised and angered Mid-South entomologists who have recently published and shared data with the EPA that directly contradict the agency’s findings.
“This conclusion really flies in the face of research we’ve been doing for the past few years,” University of Arkansas entomologist Gus Lorenz told DTN. “They’ve didn’t even include our data, and they are fully aware of it because we shared that data with them and the Canadian regulatory agency.”
Together with entomologists from the Universities of Arkansas and Tennessee and Mississippi State University, Lorenz tested pollen from corn, soybean, and cotton fields treated with neonicotinoid seed treatments in 2012 in Tennessee, Arkansas, and Mississippi. The cotton fields yielded only negligible amounts of neonicotinoids in pollen — 4 ppb was the very highest found and the average was below the detection level of 1 ppb — and no traces of the chemicals in nectar, University of Tennessee entomologist Scott Stewart said. Similar studies in 2013 and 2014 have confirmed this trend, he added.
Stewart acknowledged that foliar sprays of imidacloprid during or near to bloom could produce levels closer to the 25 ppb EPA found, but said most applications of this chemical occur prior to bloom in cotton.
The scientists also asserted that the EPA assessment misrepresented the attractiveness of cotton for honey bees.
“One of things we’ve found in our region is soybeans are highly preferred over cotton; in our surveys we have not been able to document large numbers of bees foraging in cotton fields,” Mississippi State University entomologist Angus Catchot said.
Bayer likewise objected to the assessment’s conclusions, telling DTN in an emailed statement that “at first glance it appears to overestimate the potential for harmful exposures in certain crops, such as citrus and cotton, while ignoring the important benefits these products provide and management practices to protect bees.”
A FUTURE WITH FEWER TOOLS?
Don Parker, manager of Integrated Pest Management for the National Cotton Council, said the assessment could threaten the future use of imidacloprid in cotton.
“We see a lot of errors and misrepresentations,” he said of the assessment. “As they refine it, we hope that they will correct these and see that cotton is not the high risk to bees that they claim it to be, because this product is critical for providing crop protection in the cotton industry right now.”
At the moment, cotton growers do not have any good alternatives to imidacloprid seed treatments for control of thrips, said Lorenz. The pest has widely evolved resistance to the other neonicotinoid seed treatment available, thiamethoxam (the active ingredient in Cruiser).
More on Neonicotinoids
Removing the possibility of foliar sprays of imidacloprid means growers will resort to a more applications of other chemicals such as pyrethroids and organophosphates, which are harder on the beneficial insect population that help cotton growers control secondary pests like mites and aphids, the scientists noted.
Three other neonicotinoids — clothianidin, thiamethoxam and dinotefuran — are under review by the EPA and awaiting preliminary pollinator risk assessments scheduled for release by December 2016.
The EPA’s conclusion about imidacloprid’s risk to pollinators in cotton highlights a trend that Stewart said concerns him and his fellow scientists.
“The standard I’ve seen put forward more and more by some groups is that they want an insecticide with absolutely no measurable impact on bees,” he said. “We’re dealing with insecticides — there will always be some potential risk. I thought EPA was about managing that risk and the benefits with these products, but I hear more and more rhetoric that the standard is no potential risk to pollinators at all. So this is going to happen when anything comes up for re-registration in the future and it’s going to have negative effects on agriculture.”
For now, the imidacloprid assessment has been posted to regulations.gov and is subject to a 60-day public comment period here.