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?
Research 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 could this happen?
Well we can learn much and gain many clues, by examining a manufacturer’s own product literature, and when we do so, we find:
So what can industry teach us?
What we need to ask is ‘how do neonicotinoids work to kill ‘pests’?
An 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 the UK).
Termites are social colony insects with a queen, (like bumblebees and honeybees), 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) - read more here.
Below are some general product claims
made by BayerCropScience in relation to their termite killer.
(Key: L denotes – from the leaflet for Premise 200SC; B denotes from the brochure “The Secret Life Of Termites”).
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:
Tested 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 the neonicotinoids.
The following 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.” - L
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:
“During 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.
”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.
And whilst it seems
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:
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.....
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