title: Lethal and sub-lethal effects of thymol on honeybee (Apis mellifera) larvae reared in vitro.
abstract: BACKGROUND
  Thymol offers an attractive alternative to synthetic chemicals to keep Varroa under control. However, thymol accumulates in bee products and is suspected of having adverse effects on colonies and especially on larvae. In this study, we investigated the effects of acute and chronic exposure to thymol on larvae reared in vitro with contaminated food and compared results to the theoretical larval exposure based on the amount of pollen and honey consumed by larvae during their development.
  
  
  RESULTS
  The laboratory assays reveal that, first, the 48 h-LD50 of thymol introduced into larval food is 0.044 mg larva(-1) . Second, the 6 day-LC50 is 700 mg kg(-1) food. A significant decrease of larval survival and mass occurred from 500 mg thymol kg(-1) food (P < 0.0001). Finally, vitellogenin expression, which reached a maximum at the fifth instar larvae, is delayed for individuals exposed to 50 mg thymol kg(-1) food (P < 0.0006). That is 10 times higher than the theoretical level of exposure.
  
  
  CONCLUSIONS
  Based on the level of thymol residue found in honey and pollen, these results suggest that the contamination of food by thymol represents no notable risk for the early-developing larvae.
authors.affiliation: Venoms and Biological Activities Laboratory, Jean-François Champollion University Center, EA, 4357, PRES-université de Toulouse Albi, France.
authors.forename: Gael
authors.initials: G
authors.lastname: Charpentier
authors.forename: Cyril
authors.initials: C
authors.lastname: Vidau
authors.forename: Jean-Baptiste
authors.initials: JB
authors.lastname: Ferdy
authors.forename: Jeremy
authors.initials: J
authors.lastname: Tabart
authors.forename: Angelique
authors.initials: A
authors.lastname: Vetillard
mesh_terms: D000818:Animals; D001516:Bees / Q000187:drug effects* / Q000502:physiology; D001522:Behavior, Animal / Q000187:drug effects; D007306:Insecticides / Q000633:toxicity*; D007814:Larva / Q000187:drug effects / Q000502:physiology; D013943:Thymol / Q000633:toxicity*
chemical_list: D007306:Insecticides; D013943:Thymol
keywords: honeybee; in vitro rearing; thymol; toxicity; vitellogenin