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EFFECT OF SUB-LETHAL DOSES OF SYNTHETIC AND NATURAL ACARICIDES ON HONEY BEE (Apis mellifera L.) HEALTH, MEMORY, BEHAVIOUR AND ASSOCIATED GENE EXPRESSION

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Title: EFFECT OF SUB-LETHAL DOSES OF SYNTHETIC AND NATURAL ACARICIDES ON HONEY BEE (Apis mellifera L.) HEALTH, MEMORY, BEHAVIOUR AND ASSOCIATED GENE EXPRESSION
Author: Gashout, Hanan
Department: School of Environmental Sciences
Program: Environmental Sciences
Advisor: Guzman, Ernesto
Abstract: Acaricides are applied in honey bee (Apis mellifera L.) colonies to control parasitic mites, including Varroa destructor. However, acaricides may cause adverse effects to honey bees. In three studies here reported, bees were exposed to lethal and sublethal doses of five of the most commonly used hive acaricides, and their impact on honey bee health, memory and behaviour, as well as on the immune and neural systems of bees was evaluated. Calculated LD50s showed that tau-fluvalinate is the most toxic among the tested acaricides (0.45 µg/bee), followed by amitraz (1.99 µg/bee), coumaphos (6.23 µg/bee), thymol (51.25 µg/bee) and formic acid (152.45 µg/bee). In term of hazard ratios (estimates of hive level risk), tau-fluvalinate was the most hazardous acaricide (3.6), followed by formic acid (0.9), and then amitraz, coumaphos and thymol, with the same hazard ratio (0.5). The expression of health and detoxification genes was analyzed and it was found that vitellogenin was not affected by any of the acaricides and that formic acid was the only acaricide that down-regulated cytochrome P450, suggesting that detoxification mechanisms of the exposed bees were in part compromised. Conversely, all acaricides except tau-fluvalinate increased the expression of the gene encoding acetylcholinesterase. The effect of sublethal doses (LD05) of acaricides on memory was evaluated. Formic acid significantly affected the bees’ short, mid and long-term memory, while the rest of the acaricides affected memory only in the long term. Memory related genes were analyzed and it was found that neurexin, neuroligin-1 and major royal jelly protein-1 were not affected by any of the acaricides at sublethal doses. However, thymol, formic acid, amitraz and coumaphos increased defensin-1 expression, suggesting induction of immune responses, which also could have detrimental effects in bees’ brains. The hygienic behaviour of bees was inhibited only when exposed to sublethal doses of coumaphos but not to the other acaricides, whereas tau-fluvalinate, coumaphos and formic acid reduced their foraging behaviour. Overall, it can be concluded that sub-lethal exposure to acaricides affects the health, memory and behaviour of honey bees differently, and that amitraz and thymol, appear to be the safest acaricides to bees among the five tested.
URI: http://hdl.handle.net/10214/10230
Date: 2017-01


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