Drone surrounded by worker bees. © INRA, MORISON Nicolas

Scientists flying to the rescue of bees

Stress in synergy

The excess mortality of bees can also be explained by combined causes. For example, two stress factors, such as a pathogenic agent and a pesticide, may separately have limited effects on a colony, but when they are combined the damage becomes catastrophic. A major challenge for scientists is therefore to determine these interactions between different factors and understand how together they might threaten the existence of honey bees.

Updated on 03/27/2017
Published on 05/01/2014

Viruses have their own Trojan horse

Harvesting honey from a cell using a micro-pipette. © INRA, MORISON Nicolas
Harvesting honey from a cell using a micro-pipette © INRA, MORISON Nicolas
No fewer than 25 species of virus can harm hives, and the list continues to grow.  Some of these viruses are extremely aggressive, such as Israeli acute paralysis virus which can kill bees in three days, or the chronic bee paralysis virus which immobilises the animals and causes them to tremble like a leaf. Deformed wing virus, which is very common in colonies, condemns the honey bees because their atrophied wings no longer allow them to fly. The action of these pathogens is closely linked to Varroa destructor. As viral reservoirs, these mites are the principal vector for their spread. Worse: the immunodepressive effect exerted by Varroa on honey bees places the animals at the mercy of these tiny assailants. Although viruses alone cannot explain the decline of honey bees, they are nonetheless an essential cause.  As for control measures, researchers think that first and foremost these will require the neutralisation of Varroa.

Nosema and pesticides: a fatal cocktail

The synergy between the Nosema ceranae fungus and neonicotinoid insecticides is now proven. Experiments performed by INRA in Avignon have shown that bee mortality can increase synergistically when these animals are exposed to the two factors. Scientists have also observed that this combination can impair the production of glucose oxidase, an enzyme that allows nurse bees to sterilise the food they supply to the larvae. However, it is still impossible to state how these agents "interact" in the intestine.

The search for new biomarkers

It is to Reunion Island, an oasis free of Varroa, that INRA researchers travelled to test biomarkers that can detect bees affected by pesticides and other pollutants. After exposing hives to heavily polluted or "clean" environments, the scientists compared the levels of several enzymes for metabolism, nerve transmission or immunity in the bodies of honey bees from both groups. The differences allowed them to compile an exposure profile. In the future, using these biomarker enzymes, it will be possible to determine quite simply whether an environment is harmful or not to honey bees.

Drone surrounded by worker bees. © INRA, MORISON Nicolas

A survey on the sperm quality of drones

The longevity of a queen within a colony depends on its fecundity, which in turn is dependent on the sperm she receives from males, or drones, during nuptial flight. INRA researchers in Avignon have tried to determine whether pesticides and pathogens might not damage sperm quality in bees. To test this hypothesis, it was necessary to achieve an amazing feat for the first time in the world: to rear males from birth to sexual maturity under controlled conditions. The scientists then analysed the sperm quality of these males, contaminated by pesticides, combined or not with Nosema. The preliminary findings of these ongoing studies appear to show that the quality of sperm and seminal fluid is indeed affected by these stressors. Another highlight of this work: the technique used to rear these males opens the way to beekeepers being able to select the sperm used to fertilise queens.