La infecció per Nosema ceranae, patogen responsable de la nosemiosi, augmenta la seva virulència entre les abelles quan aquestes prèviament han patit una intoxicació per insecticides. Aquesta conclusió és el resultat d'una investigació desenvolupada per tècnics del Laboratori de Microorganismes de Clermont-Ferrand i el Laboratori de Toxicologia Ambiental d'Avinyó.
Article original a Science Daily
These results are published in the journal PloS ONE.
In France, around 70 000 professional and amateur beekeepers work with honeybees (Apis mellifera).
The direct influence of bees on the quality and quantity of harvests,
as well as their role in maintaining floral biodiversity, is today
widely recognized, and highlights the key role played by both domestic
and wild bees in the functioning of ecosystems.
However, for over 15 years, bee colonies have been plagued by a
strange disease that causes the disappearance of thousands of colonies
every year and is poorly understood by beekeepers and scientists. To
explain the phenomenon, which mainly affects beekeepers in Europe and
the US, a number of factors have been suggested: biodiversity loss and
reduced quality of food resources (due to climate change), increasingly
intensive single-crop farming and modification of landscapes, pathogens
causing diseases such as varroasis (2), foulbrood (3) and Nosema, the
chemical stress resulting from the exposure of bees to veteri nary and
plant protection products, and certain predators such as the Asian giant
hornet. Although there is much data on the effect of nutritional,
parasitic and chemical stress on the health of honeybees, it has not
been possible to isolate any of these factors as being the sole cause
for the decline of bee populations. Today, specialists in the field
agree that research should focus on the combined effects of several of
these factors.
It was in this context that research teams from CNRS, INRA and
Université Blaise Pascal brought together their respective skills in
parasitology and toxicology to assess the effect of pathogen/toxin
interactions on bee health. In the laboratory, the researchers
chronically exposed newly emerged honeybees, some healthy and others
infected with Nosema ceranae, to low doses of insecticides. They found
that the infected bees died when they were chronically exposed to
insecticides, even at sublethal doses, unlike the healthy bees. This c
ombined effect on honeybee mortality was observed with daily! exposur e
to extremely low doses (over 100 times less than the LD50 (4) for each
insecticide). The synergy observed does not depend on the type of
insecticide since the two active ingredients studied, fipronil and
thiacloprid (5), belong to different groups. However, the mechanism
responsible for this synergy has not yet been identified.
This study therefore shows that interaction between Nosema disease
and insecticides represents a significant additional risk for bee
populations, and could possibly explain certain cases of excess
mortality. This work also shows that insecticide doses considered to be
non-lethal have a lethal toxic potential for organisms that are infested
with parasites and therefore vulnerable. Consequently, these findings
show that the management and protection of the bee population needs
improving, in response to the threat posed by pollution and pathogens
acting (either alone or together) on bee health. The 'Host/Parasite
Interactions' team at the Micr oorganisms: Genome and Environment
Laboratory (Laboratoire Microorganismes: Génome et Environnement (LMGE,
CNRS/Université Blaise Pascal Clermont-Ferrand 2)) are currently seeking
to find new ways of fighting this pathogen.
(1)Nosema disease is transmitted by Nosema ceranae, a microscopic fungus that colonizes the intestine of honeybees.
(2)Varroasis is a disease caused by a mite (Varroa jacobsoni) that feeds on bees' hemolymph.
(3)Foulbrood are brood diseases transmitted by bacteria.
(4)Lethal Dose 50 = a dose that causes 50% mortality in a population.
(5) These two ais belong to the phenylpyrazole and neonicotinoid insecticide groups, respectively.
Article de Science Daily
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