How Do Neonicotinoids Work?
How do neonicotinoids work? Can they kill a ‘super organism’, such as a honey bee colony?
This is an
interesting question because in colonies of social insects, individuals
typically perform specialist roles, at least for a time.
And whilst we can easily guess how insects out in the
field can come into contact with a pesticide and be poisoned, what about
those ‘back at home’ - i.e. in the insect nest?
clearly shows that a miniscule dose of a neonicotinoid may kill a bee within 48
hours, yet an even smaller dose may still be lethal…but the bee will survive longer, perhaps for example, for up to 8 days (eg. see Suchail et al 2001). This potentially gives insects time to take
a tiny dose of poison back to the colony, whilst still remaining alive, and for
this poison to be transferred around, and then cause the demise of the whole colony.
How might neonicotinoids kill a superorganism like honey bees?
learn much and gain many clues, by examining a manufacturer’s own product
literature, and when we do so, we find:
are a number of ways to kill an individual insect - not merely by immediate death through poisoning. To kill a large colony of insects may, in fact, take a little time.
- Potentially, there are multiple means of insects themselves, spreading a toxin through its colony.
damage or impair the functioning of a colony, is to kill it ultimately, but not immediately. This is recognised by industry (although, it
should be noted, the very short regulatory tests for assessing pesticides, do
not adequately test for effects on the colony functioning as a whole).
So what can
industry teach us? What we need to ask is:
manufacturers tell us neonicotinoids kill ‘pests’?
How A Neonicotinoid Kills A “Pest”: Comment And Potential Parallels With Bees
information leaflet for Bayer’s neonicotinoid Imidacloprid Termite killer:
Premise 200sc, and the Bayer brochure "The
Secret Life Of Termites” provide interesting insight into how
neonicotinoids can kill social insects (although Termites are not present in
Update May 2014: This website previously had a link to the brochure on the Bayer website, however, the company have now removed the brochure. A quote from another Bayer website has been added in the right hand margin of this page.
Termites are social colony insects
with a queen, (like bumble bees and honey bees), but their colonies can be
significantly greater – according to BayerCropScience,
they can reach from 250,000 to 3 million individuals.
Individual termites engage in roles
within the colony (e.g. foraging, nest cleaning etc). They are in a different insect order from
bees (they are of the cockroach order Blattodea). However, patents for products containing imidacloprid do claim
efficacy for controlling insects from the order Hymenoptera (to which bees
belong) – including Vespa (wasps) - see my page about neonicotinoids and non-target insects.
Below are some general product claims
made by BayerCropScience in relation to their termite killer.
L denotes – from the leaflet for Premise 200SC; B denotes from the
brochure “The Secret Life Of Termites”).
Work By Causing Disorientation, Hampering Feeding, And Paralysis
termiticides, termites cannot detect the treated zone, so they enter it and are
immediately affected. Termite stop
feeding, grooming and becomes disoriented.” - L
“Imidacloprid binds to
the nicotinergic acetylcholine receptors at the nervous systems which leads to
paralysis and eventual death”. - L
Similar effects have been noted in bees – just 2 examples:
M.E. Colin et al 2004:
both Imidacloprid and Fipronil, using dose levels 70 TIMES LOWER than the 50%
lethal dose concentration. The study found that the ability of honey bees to
forage was severely impaired. (Sub lethal doses are tiny doses that may not
kill immediately, but, for example, through impairment of physical function or
ability to fight off parasites and diseases, they do ultimately result in death).
V. Girolami et al 2009:
Fed guttation drops collected from a canola field
planted with neonicotinoid treated seeds.
When bees consumed the droplets, effects noted by Giorlami et al include
agitation, arching of the abdomen, regurgitation, uncoordinated movement, wing
paralysis, and death. As with Bayer and
their termites, Girolami found that honey bees did not appear to be repelled by
Honey bee drinking guttation.
Work By Hampering Grooming To Increase Susceptibility To Mites & Fungi
quotes suggest that by hampering the termite’s ability to groom itself, this
ultimately kills it, because it means the insect cannot clean away harmful fungal
spores it comes into contact with via the environment.
”Low doses of Premise 200SC such as
the edge of the Treated Zone, disorientate the termites and cause them to cease
their natural grooming behaviour.
Grooming is important for termites to protect them against pathogenic
soil fungi. When termites stop grooming,
the naturally occurring fungi in the soil attack and kill the termites. Premise 200 SC makes fungi 10,000 times more dangerous to termites. Nature assists
Premise in giving unsurpassed control.
This control is Premise 200SC plus Nature.” - L
”Premise 200 SC is a systemic
insecticide which acts as a contact and stomach poison. When termites come in contact with this
non-repellent product in the treated zone, the stop tunnelling, stop feeding,
grooming and they become disoriented, they will be infected by soil fungi and
die”. - L
”The termite are susceptible to
disease and fungi found in soil. A
principle part of their defence system is their grooming habits, allows the
termites to get rid of the fungal spores before these spores germinate and
cause disease of death. Premise 200SC
interferes with this natural process by lowering defence to nature’s own weaponry.”
It is well
known that insects and some other invertebrates engage in grooming behaviours
as a way of
maintaining cleanliness. Even a casual
search on YouTube reveals bees and other insects engaging in such
behaviours. See these examples:
- We know that bees groom. Grooming and social grooming in honey bees
has been detailed in a number of research studies, (for example: Moore et al
1995; Winston and Punnett, 1982; Frumhoff and Baker, 1988; Kolmes, 1989; van
der Blom, 1993).
- Importance of grooming has been
highlighted as a defence against Varroa mite in both Apis cerana (Peng et al., 1987) and Apis
mellifera (Ruttner and Haenel, 1992) and this phenomenon (termed hygenic behaviour
- Interestingly, some research suggest a
link between neonicotinoids and increased abundance of certain mites belonging,
like Varroa mite, to the arachnid taxon Acari (mites and tics)
- And the potential increase
in susceptibility to nosema fungi is explored on this
- Of course, other insects, from
butterflies to flies and beetles, all engage in grooming. In addition
to which, insects naturally make
contact with soil. Various bees, flies
and beetles nest in the soil and of course, insects will land, rest or
from puddles on the surface of soil, and hence may, like termites, have
opportunity to come into contact with pathogenic soil fungi.
Work Via Methods Of Distribution Around A Colony
their research, the experts at Bayer also discovered the ultimate benefit of
imidacloprid: the termites did not recognize the substance as being
harmful. Insects which came into contact
with imidacloprid did not display any noticeable avoidance behavior, and passed
it on to other inhabitants of the colony. The Bayer team concluded from this
that imidacloprid can be distributed via the cuticle of the termites. However,
some insects also ingest it and pass it on by regurgitation.” - B
”When one termite meets another, it
uses its mouthparts to clean and tidy it.
This behavior, which scientists
refer to as ‘grooming’, opens up an opportunity for more effective control of termites, as it allows an active substance to be
passed from one insect to the next. This mode of transmission helps
imidacloprid reach the furthest corners of the complex system of tunnels inside
a termite nest, so that it has the potential to affect the entire population
very quickly,” - B
literature from Bayer suggests there are multiple ways in which a pesticide may
be spread throughout the colony, but this also presupposes that acute mortality
(i.e. immediate death) does not always happen.
Rather, the insect may certainly survive long enough to pass on the
poison to other colony members, via the cuticle or regurgitation and via grooming.
Although the hampering of grooming may mean
the individual termite succumbs to pathogenic fungi, it is interesting that
what can also happen is that social grooming becomes a method of spreading the
poison through the colony.
- EFSA have
stated that guidelines provide inadequate study of colony effects. The regulatory EPPO guidelines for testing pesticides
on bees, do not assess for the varying methods of transferring of a pesticide
through the colony. The field tests
being only of 28 days required duration, and the semi-field tests of only 7
days, have no requirement for, nor a realistic method of observing multiple
distribution routes through the colony.
- Honey bees
engage in social grooming as previously discussed, but they also engage in ‘trophallaxis’ – the act of communicating
whilst feeding each other due to
the passing on of bee pheromones.
- Honey bees are a key
species for pesticide testing, but what is also still unclear is how smaller
colonies of non-target invertebrates with shorter colony life spans and lower
average survival rates, may be affected and may transfer poison around a colony.
Work By Damaging The Colony. Colony Impairment Is Ultimately Colony Demise
”Termite colonies work
as interdependent units – they all rely on each other for survival. Premise 200
SC interferes with this instinctive social behaviour, contributing to the
termites’ demise.” - L
“Genetic analysis from
the house studies has now proven this. Feeding on the wooden structure was
stopped in days, termites disappeared within a week or two from soil monitors
immediately outside the structure, and after three months all termite
colonies attacking these structures were eliminated. After two years of
monitoring since treatment, not one of these colonies has recovered.“ - B
Bayer CropScience find that by impairing some of the termites,
ultimately the whole colony is affected due to the interdependence of the
colony on all termites performing their colony roles.
Colony destruction may take 3 months, but
won’t recover even after 2 years.
Bayer CropScience acknowledge that death of a termite colony may take 3
months, nevertheless, EPPO standards
used by manufacturers for field trials of pesticides on honey bees require a test of 28 days ONLY.
And that's not all:
- The inadequacies of EU regulatory assessment guidelines was outlined thoroughly in
2006 by HALM et al, who also noted that in complex colonies of species such as honey bees, the health of each unit is essential to maintain the health of the whole
(citing Moritz, R.F.A; Southwick, E.E Bees as superorganisms, an evolutionary reality;
Springer-Verlag: Berlin, 1992; 395 pp).
tests assessing colony behaviour are inadequate, and need to take into account:
• Specialisation in the hive
• Bees with different roles in the hive have different diets
• Bees in different life
stages have different diets
• Bees with different roles have
different critical sensitivities to different sub-lethal effects.
- How might
species producing smaller colonies be affected?
Clues can be found in “Neonicotinoid Pesticide Reduces Bumble Bee Colony
Growth and Queen Production” – by Whitehorn
et al April 2012, who found that “Treated
colonies of bumblebees had a significantly reduced growth rate and suffered an
85% reduction in production of new queens compared with control colonies”.
- Impairment of colony function has been noted in bumblebees - in particular, by affecting them within their roles, hence impairing the colony - Gill et al
(Oct 2012) “Combined pesticide exposure severely affects individual and
colony-level traits in bees” -doi:10.1038/nature11585:
“chronic exposure of bumblebees to two pesticides (neonicotinoid and pyrethroid)
at concentrations that could approximate field-level exposure impairs natural
foraging behaviour and increases worker mortality leading to significant
reductions in brood development and colony success. We found that worker
foraging performance, particularly pollen collecting efficiency, was
significantly reduced with observed knock-on effects for forager recruitment,
worker losses and overall worker productivity”.
- In 2003, a
scientist from the National Bee Unit, Sand Hutton York, a department of FERA,
published a paper: Thompson, H.M (2003) Behavioural effects of pesticides in bees – their
potential for use In risk assessment Ecotoxicology 12 317-330.
reviewed “a variety of behavioural effects that have been reported in bees following
exposure to pesticides, primarily insecticides”. A number of studies detailing a variety of
behavioural effects, are summarised in tables.
notes that “there is currently little
guidance available on the types of behavioural data which should be collected
during laboratory, semi-field or field regulatory studies or how they should be
included and interpreted in risk assessment.
Further work is required to include significant behavioural effects and
their longer term consequences on colony survival and development”.
notes the EPPO guidelines and that they refer to foraging activity and
behaviour of bees on the crop and around the hive, but states “The review presented here has shown that
there are a number of behavioural effects that could have a severe effect on
colony development and survival but the longer-term impact on the colony is
- It's not surprising that EFSA
outlined a number of weaknesses in the regulatory assessments for pesticides,
including those that failed to assess behavioural, larval, colony and chronic
In conclusion I think it really is worth understanding how neonicotinoids work with respect to 'pests', because it may tell us something about their potential effects on bees.
Indeed, clues are sometimes provided by manufacturers within their own product literature. I have sent this information to our responsible government ministers, but apparently, they are not interested.....