Immune suppression by neonicotinoids could be at the root of insect decline

Scientists have identified infectious diseases as a key driver of bee population decline and have shown for the first time the extent to which the diseases are shared with other pollinator groups, in research published this week. Researchers from Royal Holloway, University of London, Oxford University and Cornell University have shown that viruses that are harmful to honeybees are also present in hoverfly pollinators. The study suggests that hoverflies are exposed to the same diseases, and may move the infections around when they feed from the same flowers as the honeybees.

Hoverflies are very mobile - unlike honeybees - and can undertake large-scale annual migrations. Thus the study suggests hoverflies have the potential to spread diseases throughout landscapes, or even across entire continents. Global declines of insect pollinators jeopardise the delivery of pollination services in both agricultural and natural ecosystems. Dr Emily Bailes, post doctoral research assistant at Royal Holloway, who led the research, said: “We have seen a decline in bees in the UK for several years, but this study shows for the first time that hoverflies may be moving these diseases much further than bees normally would.

“This is because of their annual migrations across Europe. This could expose local bee populations to new strains of the diseases and make them more likely to become infected, much like different flu strains in humans. We therefore need to think of ways to limit this transfer between species.

“What we don’t know yet is whether the hoverflies are just moving the diseases around, or if [the diseases] are also causing harm to the hoverflies. This is important to find out because hoverflies are also extremely valuable pollinators, and several species are known to be in decline.”

During the study, honeybees and four of the most common species of hoverfly were collected from grassland and woodland near Oxford. The samples were screened for the six most common honeybee viruses, of which three were detected in both honeybees and hoverflies.

Professor Owen Lewis, from Oxford University and senior author of the paper, added: “Most people think of honeybees as the main pollinators of our crops and wildflowers.

"However, wild insects such as hoverflies are hugely important too. The new results suggest that the fates of these pollinating insects may be tightly linked, if diseases such as viruses can spread between them.”

Source: Catherine Harte in The Ecologist, 1 March 2018…
This story is based on a news release from Royal Holloway, University of London.

Outbreaks of infectious diseases in honey bees, fish, amphibians, bats and birds in the past two decades have coincided with the increasing use of systemic insecticides, notably the neonicotinoids and fipronil. A link between insecticides and such diseases is hypothesised. Firstly, the disease outbreaks started in countries and regions where systemic insecticides were used for the first time, and later they spread to other countries. Secondly, recent evidence of immune suppression in bees and fish caused by neonicotinoids has provided an important clue to understand the sub-lethal impact of these insecticides not only on these organisms, but probably on other wildlife affected by emerging infectious diseases.

Rosemary Mason, Henk A Tennekes, Francisco Sanchez-Bayo, Palle Uhd Jepsen (2012) Immune suppression by neonicotinoid insecticides at the root of global wildlife declines. Journal of Environmental Immunology and Toxicology 2013; 1:3-12. DOI: 10.7178/jeit.1