[Pollinator] Purdue University -- Corn seed treatment insecticides pose risks to honey bees, yield benefits elusive

[Matthew Shepherd]

A news release from Purdue University:



*Corn seed treatment insecticides pose risks to honey bees, yield benefits
elusive*



https://www.purdue.edu/newsroom/releases/2017/Q2/corn-seed-treatment-insecticides-pose-risks-to-honey-bees,-yield-benefits-elusive.html

May 22, 2017



WEST LAFAYETTE, Ind. – Nearly every foraging honey bee in the state of
Indiana will encounter neonicotinoids during corn planting season, and the
common seed treatments produced no improvement in crop yield, according to
a Purdue University study
<http://onlinelibrary.wiley.com/doi/10.1111/1365-2664.12924/full>. (Click
http://purdue.ag/perilstopollinators for a video abstract).



Neonicotinoids, including clothianidin and thiamethoxam, are a class of
insecticide commonly applied as a coating to corn and soybean seeds to
protect them from early-season pests. Since the coatings are sticky, a talc
or graphite powder is added to vacuum systems in planters to keep the seeds
from clumping. Powder exhausted from the planter contains neonicotinoids.



The United States is losing about one-third of its honeybee hives each
year, a significant problem since the bees pollinate many crops used to
feed people and livestock. Neonicotinoids, which are highly toxic to
honeybees, are being scrutinized as a possible contributor to the losses.



Christian Krupke, a professor of entomology, showed in 2012
<http://www.purdue.edu/newsroom/research/2012/120111KrupkeBees.html> that
exhausted insecticides collected on flowers that border agricultural fields
and were present in hives near those fields. Bees in those hives showed
physical signs of insecticide poisoning, and dead bees tested positive for
the neonicotinoids used as seed treatments of corn and soybeans.



Now, Krupke, along with collaborators Jeff Holland at Purdue, Elizabeth
Long at Ohio State University, and Brian Eitzer with the Connecticut
Agricultural Experiment Station, have measured the drift of those
neonicotinoids from fields and found that the insecticides can settle on
flowers up to 100 meters from the edge of the planted fields, the farthest
distance examined in the study. Their findings are published in the Journal
of Applied Ecology.



Mapping Indiana’s corn acreage, as well as the areas that may receive
drift, the authors say that 42 percent of the state is exposed to
neonicotinoids during crop planting. Looking at public data on the location
of apiaries and projecting the range that honey bees forage, they found
that 94 percent of bees could fly through areas that contain lethal doses
of the insecticides during the period when corn is planted.



“Our previous study showed that these neonicotinoids are likely to leave
the field, but we wanted to demystify that distance and show how far the
material moves, at what concentrations and what the actual risk is,” Krupke
said. “There was a misconception that any bees not living near corn were
likely to be fine. But that’s not true, and it’s clear that these
insecticides are reaching into the places bees forage and putting them at
risk.”



Krupke’s team set up dust collection stations at 12 Indiana fields where
corn was being planted and collected samples for two years at distances up
to 100 meters. Analysis of the collected dust showed lethal doses of
neonicotinoids were reaching the farthest traps. Added to the clouds over
the fields during planting, Krupke said bees are exposed to significant
risk.



“As planter exhaust is blown up and away from the equipment, it gets into
the air stream and is at the mercy of whatever is going on with the wind,”
Krupke said. “It’s not all that different from the pesticide drift that
we’ve talked about for years, but these products were supposed to solve
that problem. Now we know that they also drift.”



In the same study, the researchers found no evidence that neonicotinoids
increased yield in corn. The authors tested untreated corn seed, and seeds
coated with neonicotinoids and fungicides at both high and low doses, at
three locations around Indiana. There were differences in pest damage at
one site, but those did not translate into yield loss.



The authors conclude that the lack of benefit for corn yields in their
study, as well as inconsistent findings in U.S. corn, soybean and oilseed
rape in Europe, “suggest that the current use levels of insecticidal seed
treatments in North American row crops are likely to far exceed the
demonstrable need, and our results likely reflect a scarcity of target
pests.”



The industry continues to work on alternative seed lubricants to reduce
dust movement at planting, but to date progress has been limited. According
to a Penn State study analyzing USDA pesticide use data, the rates of
neonicotinoid use in corn have doubled since 2012.



Finally, the authors say that the risk to bees and other non-target
organisms could be more significant than their paper suggests. They only
examined cornfields in this study, and soybeans are also typically treated
with neonicotinoids. The study transects were limited to 100 meters from
field edges, but it’s possible that lethal doses reach further. And they
did not account for the fact that bees create static charges on their
bodies during flight, which means they may be attracting
insecticide-tainted dust during flight and not just when landing on flowers.



Neonicotinoids are on almost all corn and most soybean seeds sold in the
U.S., though Krupke said that this study and other reports of inconsistent
yield benefits, show that widespread use is unnecessary and farmers could
benefit from access to seeds not treated with insecticide. He will focus
research on determining the circumstances in which neonicotinoids are
useful for improving yield, and he will encourage farmer access to
neonicotinoid-free seed, which is almost non-existent in the current market.



“The good news is that because farmers often don’t need these additions to
seeds or benefit from them, we can easily and rapidly reduce the risk
simply by having untreated seeds available,” Krupke said. “That would also
allow farmers to make some side-by-side comparisons in their own fields.”



The U.S. Department of Agriculture and the Indiana Corn Marketing Council
supported the research.



Contact: Shari Finnell, 765-494-2722, sfinnell at purdue.edu

Source: Christian Krupke, 765-494-4912, ckrupke at purdue.edu

________________________________________



ABSTRACT



Planting of neonicotinoid-treated maize poses risks for non-target
organisms over a wide area without consistent crop yield benefit

C. H. Krupke1, J. D. Holland1, E. Y. Long2, and B. D. Eitzer3

1. Department of Entomology, Purdue University.

2. Department of Entomology, The Ohio State University.

3. Connecticut Agricultural Experiment Station.



1. Neonicotinoid insecticides are used as seed treatments on most grain and
oilseed crops in the US, yet the extent and likelihood of spread of
insecticide residues during planting has not previously been quantified.



2. Honey bees are the best model for estimating exposures in mobile
insects. We measured neonicotinoid dust drift during maize sowing and used
sites of maize fields, apiary locations and honey bee foraging radii to
estimate likelihood of forager exposure. We performed a concurrent
multi-year field assessment of the pest management benefits of
neonicotinoid-treated maize.



3. Our results indicate that over 94% of honey bee foragers throughout the
state of Indiana are at risk of exposure to varying levels of neonicotinoid
insecticides, including lethal levels, during sowing of maize. We
documented no benefit of the insecticidal seed treatments in terms of crop
yield during the study.



4. Synthesis and applications: We demonstrate that the likelihood of
exposure for non-target lands and the primary agricultural pollinator
species, Apis mellifera, is high during sowing of neonicotinoid treated
maize seed in a representative agricultural state in the US. This pest
management approach has potential to contaminate non-target lands and
waterways; we estimate that over 42% of the state of Indiana will encounter
deposition of neonicotinoid residues during the period of maize sowing.
However, we also demonstrate that the risks to pollinators and other
sensitive organisms can likely rapidly and dramatically reduced without
yield penalties, by aligning use rates of neonicotinoid insecticides with
pest incidence.
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