'Partially banned' insecticides affect bees' cells

Research published this week in the journal Environmental Toxicology and Chemistry suggests that broad-spectrum systemic insecticides, fipornil and imidacloprid, reduce mitochondrial activity in honeybees. Mitochondria are tiny components of cells that convert food energy into a form the cell can use.

The authors investigated the effects of fipronil and imidacloprid on the bioenergetic functioning of mitochondria isolated from the heads and thoraces of Africanized honeybees. The researchers said the observed effects on mitochondrial activity result in depleted cell energy, which could explain the toxicity of these compounds for honeybees.

Although the two chemicals studied have been subjected to partial restrictions in the EU, they are still widely used in agriculture elsewhere. In June, a task force convened by IUCN, publishing its findings on systemic insecticides, warned that pyrazoles including Fipronil and neonicotinoids such as imidacloprid pose a threat to life at all levels of an ecosystem. 

In response to population declines observed across the Northern Hemisphere, there has been a greater focus on the impacts of certain pesticides on bees and other (non-target) insect pollinators in recent years. Although the products' manufacturers deny that pesticides are impacting on pollinator health, arguing that habitat loss and disease are the main factors in declines, independent scientists are increasingly suggesting there may be more to the problem.

Scientists are urgently trying to determine the causes of colony collapse disorder and the alarming population declines seen in bee populations. As with the research published this week, studies have mostly focused on honeybees, which have been domesticated and managed by humans, though wild pollinators are facing similar challenges, and there is a lack of research and information on their plight.

Worldwide, insects such as bees pollinate approximately 80 percent of all flowering plants, and a third of all agricultural food crops.

Daniel Nicodemo, professor of ecology and beekeeping at the Universidade Estadual Paulista in Dracena, Brazil, said that the effects of pyrazoles and neonicotinoids on the nervous system are fairly well documented. Professor Nicodemo added, "These insecticides affect the nervous system of pest and beneficial insects, often killing them. Sublethal effects related to insect behavior have been described in other studies; even a few nanograms of active ingredient disturbed the sense of taste, olfactory learning and motor activity of the bees."

A key characteristic of colony collapse disorder is the incapacity of honeybees to return to their hives, and these disruptions have a direct impact on that ability.

Prof Nicodemo's findings relate to cell energy; honeybee flight muscles are strongly dependent on high levels of oxygen consumption and energy metabolism. The professor warned that any effects on mitochondrial activity could impact on muscle activity during flight.

 "If something goes wrong, the energy production is impaired. Similar to a plane, honeybees require clean fuel in order to fly," Nicodemo explained, adding that both fipronil and imidacloprid could affect bees' ability to forage and return to the hive, even at sublethal levels, where insecticide damage may not be immediately evident.

Click here to access the original paper.