Certain insecticides used in agriculture have been linked to the sudden disappearance of honeybee colonies. These chemicals, which are typically used to protect crops from harmful pests, may be doing the opposite by compromising bee immunity and in turn killing the pollinators that play a crucial role in our food industry.
A recent study published in the Proceedings of the National Academy of Sciences tested the effect of a type of controversial and currently used insecticide, called neonicotinoids, on the health and vitality of honeybees. Scientists found that even in small doses this chemical reduced the bees’ ability to fight off viruses, leading to a condition that could cause their wings to become deformed.
With defective wings, the normally efficient honeybees are unable to perform the crucial task of flying from flower to flower to collect nectar and their lifespans are drastically shortened. Furthermore, the infection easily spreads through the confined beehive and can eventually lead to the collapse of the entire colony, creating major problems for the agriculture that depends on pollination.
With his team of scientists, Dr. Gennaro Di Prisco collected experimental data to show exactly how the destructive insecticide alters bee immunity and to ultimately provide insight on honeybee conservation and negative agricultural practices.
First performing tests on fruit flies, the scientists applied neonicotinoid insecticides onto the exterior body of the insects and found that this led to challenges in their immune systems. They also performed a similar experiment to test a different type of insecticide called chlorpyrifos, but found that this did not affect the flies’ immunity.
Considering the results from the fly experiments, the researchers moved on to testing honeybees to see if there would be a similar impact. They monitored immune signals in the bees as they gave them small doses of the two different insecticides followed by exposure to a common virus.
As expected, the bees that came in contact with the neonicotinoid chemicals had weakened immune responses while those that remained unexposed were able to fight off the infection. In further accordance with the fly testing, the chlorpyrifos insecticide did not affect bee immunity.
They also tested the relationship between the insecticide and the prevalence of deformed winged virus and saw that increasing doses of the neonicotinoids led to a higher frequency of the virus within experimental bees.
While these experiments demonstrated the damaging effect of neonicotinoid insecticides, they did not adequately predict if the same outcome would occur outside of the laboratory.
To simulate more realistic conditions the scientists fed the honeybees nectar mixed with trace amounts of the insecticide over a prolonged period of time, as would be the case in their natural environment. Nevertheless, the researchers still found that the neonicotinoid insecticide caused the bees to have a higher susceptibility to infection and develop more cases of deformed wing virus.
Apiaries across the globe have seen a decrease in bee colonies and increasingly frequent incidences of deformed wing virus. Although a few countries have restricted the use of neonicotinoid insecticides, they are still available in many places.
Declining health and longevity of honeybees as well as the collapse of entire bee colonies can be attributed to the use of this dangerous insecticide. Without the implementation of new and sustainable agricultural practices for pest control, human health could eventually follow that of the honeybees.
Formal Post by Shireen Usman
Prisco, G. D., and Cavaliere, V., et al. (2013). Neonicotinoid clothianidin adversely affects insect immunity and promotes replication of a viral pathogen in honey bees. PNAS early edition, 1-6.