title: Exposure to sublethal doses of fipronil and thiacloprid highly increases mortality of honeybees previously infected by Nosema ceranae.
abstract: BACKGROUND
  The honeybee, Apis mellifera, is undergoing a worldwide decline whose origin is still in debate. Studies performed for twenty years suggest that this decline may involve both infectious diseases and exposure to pesticides. Joint action of pathogens and chemicals are known to threaten several organisms but the combined effects of these stressors were poorly investigated in honeybees. Our study was designed to explore the effect of Nosema ceranae infection on honeybee sensitivity to sublethal doses of the insecticides fipronil and thiacloprid.
  
  
  RESULTS
  Five days after their emergence, honeybees were divided in 6 experimental groups: (i) uninfected controls, (ii) infected with N. ceranae, (iii) uninfected and exposed to fipronil, (iv) uninfected and exposed to thiacloprid, (v) infected with N. ceranae and exposed 10 days post-infection (p.i.) to fipronil, and (vi) infected with N. ceranae and exposed 10 days p.i. to thiacloprid. Honeybee mortality and insecticide consumption were analyzed daily and the intestinal spore content was evaluated 20 days after infection. A significant increase in honeybee mortality was observed when N. ceranae-infected honeybees were exposed to sublethal doses of insecticides. Surprisingly, exposures to fipronil and thiacloprid had opposite effects on microsporidian spore production. Analysis of the honeybee detoxification system 10 days p.i. showed that N. ceranae infection induced an increase in glutathione-S-transferase activity in midgut and fat body but not in 7-ethoxycoumarin-O-deethylase activity.
  
  
  CONCLUSIONS
  After exposure to sublethal doses of fipronil or thiacloprid a higher mortality was observed in N. ceranae-infected honeybees than in uninfected ones. The synergistic effect of N. ceranae and insecticide on honeybee mortality, however, did not appear strongly linked to a decrease of the insect detoxification system. These data support the hypothesis that the combination of the increasing prevalence of N. ceranae with high pesticide content in beehives may contribute to colony depopulation.
authors: Clermont Université, Laboratoire Microorganismes: Génome et Environnement, BP 10448, Clermont-Ferrand, France.
authors: Cyril
authors: C
authors: Vidau
authors: Marie
authors: M
authors: Diogon
authors: Julie
authors: J
authors: Aufauvre
authors: Régis
authors: R
authors: Fontbonne
authors: Bernard
authors: B
authors: Viguès
authors: Jean-Luc
authors: JL
authors: Brunet
authors: Catherine
authors: C
authors: Texier
authors: David G
authors: DG
authors: Biron
authors: Nicolas
authors: N
authors: Blot
authors: Hicham
authors: H
authors: El Alaoui
authors: Luc P
authors: LP
authors: Belzunces
authors: Frédéric
authors: F
authors: Delbac
mesh_terms: D000818:Animals; D001516:Bees / Q000187:drug effects* / Q000382:microbiology*; D007306:Insecticides / Q000633:toxicity*; D000073943:Neonicotinoids; D016818:Nosema / Q000472:pathogenicity*; D011720:Pyrazoles / Q000633:toxicity*; D011725:Pyridines / Q000633:toxicity*; D013843:Thiazines / Q000633:toxicity*
chemical_list: D007306:Insecticides; D000073943:Neonicotinoids; D011720:Pyrazoles; D011725:Pyridines; D013843:Thiazines; C417209:thiacloprid; C082360:fipronil