Neonicotinoid Thiamethoxam Impairs Honey Bee Flight
This is a brief review of a scientific paper published in 2017:
Tosi, Simone & Burgio, Giovanni & Nieh, James. (2017).
"A common neonicotinoid pesticide, thiamethoxam, impairs honey bee flight ability."
Scientific Reports. 7. 1201. 10.1038/s41598-017-01361-8.
Quote From The Abstract
"Pesticides can pose environmental risks, and a common neonicotinoid pesticide, thiamethoxam, decreases homing success in honey bees.
Neonicotinoids can alter bee navigation, but we present the first evidence that neonicotinoid exposure alone can impair the physical ability of bees to fly.
We tested the effects of acute or chronic exposure to thiamethoxam on the flight ability of foragers in flight mills.
Within 1 hr of consuming a single sublethal dose (1.34 ng/bee), foragers showed excitation and significantly increased flight duration (+78%) and distance (+72%).
Chronic exposure significantly decreased flight duration (−54%), distance (−56%), and average velocity (−7%) after either one or two days of continuous exposure that resulted in bees ingesting field-relevant thiamethoxam doses of 1.96–2.90 ng/bee/day.
These results provide the first demonstration that acute or chronic exposure to a neonicotinoid alone can significantly alter bee flight.
Such exposure may impair foraging and homing, which are vital to normal colony function and ecosystem services."
As discussed elsewhere on this website, neonicotinoid
pesticides are very widely used across the global, and on a very broad range of
Above: Honey bee drinking guttation on leaf stem
They are known to persist in the
environment after their use.
purposes of reviewing the above study, it is also important to remember that
after use, neonicotinoids can be found:
- in the nectar and pollen of plants
visited by honey bees, and
- in the guttation (the drops of sap that gather
on the leaves and stems of some plants – including those favoured by
Thus, bees visiting and feeding
on such plants will be routinely exposed to neonicotinoid pesticides.
The authors of the above paper also note that other studies have shown:
- that chronic exposure to
neonicotinoids can occur because bees can survive a single small dose but can
then return to forage at the same contaminated food source, and
- that bees seem to
prefer sucrose solutions containing neonicotinoids over pure sucrose – meaning
that they return repeatedly to the contaminated food source.
neonicotinoid pesticides (e.g. clothianidin, imidacloprid and thiacloprid) can
impair bee navigation, foraging, homing and locomotion.
Varroa-Free Bees Tested
Some of the studies examining the effect of
neonicotinoid pesticides have been carried out using bee colonies known to have
measurable levels of Varroa and it
appears that the effect of the neonicotinoids used in these studies may be a
synergistic one between neonicotinoid and Varroa,
which leads to impaired flight distance in the bees.
It has also been previously shown that ‘second
generation’ neonicotinoid (thiamethoxam = TMX) reduces ‘forager return’ rates
to the nest (i.e. in bee colonies that consume TMX, there is an increase in the
number of bees that fail to return to the nest from foraging trips), suggesting
that TMX impairs navigation or flight ability or both.
The bee colonies used in this study did not have any
measurable levels of Varroa, so the
study demonstrates a direct effect of the study compound (thiamethoxam - TMX),
rather than merely a synergistic effect between neonicotinoid and Varroa.
study demonstrates that TMX alone impairs the physical ability of bees to fly.
Key Study Design Features
The study was performed on 19 colonies – all confirmed not
to have measurable levels of Varroa.
scientists used tethered bees in flight mills (a standard way of examining bee
flying capabilities) to examine flight distance, flight duration, and flight
velocity in bees.
- TMX in the treated group did not increase mortality (death) compared
to the control group – it was a sub-lethal dose of TMX used. This means that all the bees involved in the study remained
alive for the duration of the study. (Bees in the control group were given glucose
solution without the TMX.)
- The scientists examined both
the acute (short-term) and chronic (long-term) effects. They examined four parameters in each part:
- duration of flight;
- distance flown;
- mean velocity;
- maximum velocity.
- To measure the acute effects of TMX
exposure, each bee flew twice – once before exposure to TMX and again after
exposure to TMX (glucose solution with 1.34ng TMX). To measure the effects of chronic
exposure to TMX, each bee flew just once after one or two day exposure.
‘immediate’ effect of TMX exposure was an increase in parameters measured: flight
time; flight distance and mean flight velocity – i.e. bees exposed to TMX flew
longer, further, and quicker than non-exposed bees. The effect of TMX was noted to occur within 1
hour of exposure.
- Although the acute effect of TXM exposure seems to be positive
(greater duration and distance of flight), it is actually negative, because it
leads to exhaustion and energy depletion in individual bees.
- Additionally it has also been shown that
similar doses of neonicotinoids also create ‘flight disorientation’ – bees fly
more erratically and for longer distances, thus reducing the possibility of
them successfully returning to the nest.
- The scientists used four different
concentrations of TMX – 1.95ng, 2.90ng, 3.71ng, 4.53ng. Even the largest of these doses is
significantly lower than the ‘worst case scenario’ volume that bees might
consume in the wild according to an EFSA estimate.
scientists showed that chronic exposure to TMX reduce flight time, flight
distance, and flight velocity.
The authors of this study state that a sub-lethal dose or
chronic neonicotinoid exposure is sufficient to significantly alter honey bee
flight ability. This alteration may
impair foraging and homing in affected bees – thereby creating a negative
impact on colony function.
How do neonicotinoids work to kill insects like bees?
Manufacturers provide clues!
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