Evaluation of Dry and Wet Formulations of Oxalic Acid, Thymol, and Oregano Oil for Varroa Mite (Acari: Varroidae) Control in Honey Bee (Hymenoptera: Apidae) Colonies.

The efficacy and safety of dry and wet formulations of three nonsynthetic compounds, oxalic acid (OA), thymol (T), and oregano oil (OO), for the control of Varroa destructor Anderson and Trueman infestations in honey bee (Apis mellifera Linnaeus) colonies were determined. The treatments were OA in dust, OA diluted in glycerin solvent embedded in a towel, T in dust, T in glycerin solvent and towel, OO in dry microcapsules, OO in glycerin solvent and towel, and the control. The treatments were applied weekly for 4 wk during the fall season. The rates of acaricide efficacy, weekly mite fall, bee mortality, colony survivorship, and strength, were determined for each of the treatments. All formulations, with the exemption of OO microcapsules, were effective at controlling infestations of V. destructor. The most effective formulations were T dust (96.6%), T glycerin (92.4%), and OA glycerin (79%). More than 85% of the mites were killed during the first 2 wk of treatment with T formulations, compared to less than 30% for the OA glycerin formulation. The lowest efficacy rate was for OO microcapsules (21.3%), and the only treatment that significantly increased bee mortality was OA glycerin. The rates of winter colony survival and honey bee populations were related to the varroacidal efficacy of the formulations. The implications of these findings are discussed.

Impact of sublethal exposure to synthetic and natural acaricides on honey bee (Apis mellifera) memory and expression of genes related to memory.

Acaricides are used by beekeepers in honey bee (Apis mellifera L.) colonies to control parasitic mites, but may also have adverse effects to honey bees. In this study, five commonly used acaricides were tested for their sublethal effects on memory and expression of neural-related genes in honey bees. Memory measured with the proboscis extension reflex (PER) assay was significantly reduced by topical treatment of bees with a single LD05 dose of formic acid at 2 and 24 h post treatment (hpt). However, tau-fluvalinate, amitraz, coumaphos, and formic acid, but not thymol, resulted in memory loss at 48 hpt. The LD05 doses of the acraricides did not affect expression of neuroligin-1, related to memory, or expression of major royal jelly protein-1, related to both memory and development, although expression of both genes was affected at LD50 doses. The LD05 doses of thymol, formic acid, amitraz and coumaphos increased defensin-1 expression, which is related to both memory and immunity. The effect of thymol, however, may have been due to its impact on the immune response rather than memory. This study demonstrates that acaricides vary in their effects on bee's memory, and that the widely used acaricide, formic acid, is particularly damaging.

Evidence of presence and replication of honey bee viruses among wild bee pollinators in subtropical environments.

We determined the presence of six viruses in different bee species collected in subtropical environments. Deformed wing virus (DWV) and black queen cell virus (BQCV) were detected in >90% of honey bee samples and in 50-100% of four stingless bee, two bumble bee and one solitary bee species. Additionally, minus DWV and BQCV RNA strands were detected, indicating that the viruses replicate in several hosts. This is the first report of honey bee viruses replicating in six wild bee species in the tropics. If pathogenic to them, viral infections could result in negative impacts in agricultural and unmanaged ecosystems.

Lethality of synthetic and natural acaricides to worker honey bees (Apis mellifera) and their impact on the expression of health and detoxification-related genes.

In this study, honey bees (Apis mellifera L.) were exposed to LD05 and LD50 doses of five commonly used acaricides for controlling the parasitic mite, Varroa destructor. LD50 values at 48 h post-treatment showed that tau-fluvalinate was the most toxic, followed by amitraz, coumaphos, thymol, and formic acid. However, the hazard ratios, which estimate the hive risk level based on a ratio of a standard dose of acaricide per hive to the LD50 of the acaricide, revealed that tau-fluvalinate was the most hazardous followed by formic acid, coumaphos, amitraz, and thymol. The expression of the honey bee acetylcholinesterase gene increased after treatment with the LD05 and LD50 acaricide doses and could distinguish three patterns in the timing and level of increased expression between acaricides: one for amitraz, one for tau-fluvalinate and formic acid, and one for coumaphos and thymol. Conversely, changes in cytochrome P450 gene expression could also be detected in response to all five acaricides, but there were no significant differences between them. Changes in vitellogenin gene expression could only detect the effects of tau-fluvalinate, amitraz, or coumaphos treatment, which were not significantly different from each other. Among the acaricides tested, coumaphos, amitraz, and thymol appear to be the safest acaricides based on their hazard ratios, and a good marker to detect differences between the effects of sub-lethal doses of acaricides is monitoring changes in acetylcholinesterase gene expression.