By
Dr Mary F Coffey
For many decades, Irish beekeepers have been aware of the negative impact which pesticides are having on the health and vitality of colonies and have campaigned to limit the use of pesticides in agriculture. However, when the Varroa mite (Varroa destructor) arrived to Ireland in the late 1990s, which subsequently increased the risk of beekeepers experiencing unacceptably high winter losses, beekeepers relationship with pesticides appeared to change and many justified the placement of a pyrethroid pesticide (flumethrin-Bayvarol) directly into the bee colony. Over the past two decades due the continuous use of Bayvarol in colonies, the results of a national study carried by DAFM in 2010, showed that the Varroa mite population in Ireland has successfully developed resistance to this chemical and thus can no longer be relied on as a treatment for the effective control of the mite. The Federation of Irish Beekeepers Association (FIBKA ) responded to this development by campaigning for the authorisation of an alternative chemical based product, and in 2017 an Amitraz based product, commercially known as ApiVar was authorised and is now freely available to beekeepers. Although pesticides appear to be the easiest and surest means of controlling Varroa mite effectively and hence ensuring a healthy and productive colony, there in increasing evidence that pesticides, including varroacides are having negative sub-lethal effects on the overall health of the bee and subsequently the vitality of the colony.
So this begs the question; are their alternatives to maintaining a relatively pest free and healthy bee colony without the continuous use of pesticides. For the hobbyist and even the professional beekeepers the answer is yes, but it will require the beekeeper to adopt IPM
IPM, stands for integrated pest management and is a phrase familiar to many beekeepers. Pest management, as opposed to pest eradication means that that the pathogen will remain in the colony, but damage caused will be at a level which can be tolerated by the colony. This level is called the economic injury level. IPM is a sensitive approach to pest management which utilises a combination of practices to control the pathogen rather than relying on a single pest control scheme, namely a chemical pesticide. However, it should be noted that in most IPM systems chemical pesticides continue to play a crucial role, but in general should only be administered when the pathogen load becomes critical and also longer periods need to elapse between individual treatments.
There are eight basic principles in any IPM programme:
- Acceptable pest levels
- Preventive culture
- Monitoring practices
- Genetic control
- Mechanical control
- Physical control
- Biological control
- Chemical control
In an IPM programme for the effective control of the Varroa mite, low levels of Varroa mites will reside in the colony throughout the season. The importation of live bees should be avoided as this reduces the risk of importing new infections of existing pathogens and/or the importation of new additional exotic pathogens such as the Asian hornet and/or the small hive beetle. Furthermore, the importation of live bees could potentially introduce into the Varroa population in Ireland, mites which have already developed resistance to the most recently authorised Varroa treatment, ApiVar . By natural selection these resistant Varroa mites could quickly develop into a resistant mite population and subsequently the effective life of ApiVar would be significantly reduced.
A good understanding of the biology and behaviour of the Varroa mite along with early detection will offer the beekeeper time to use non-chemical options. Numerous reliable and well tested monitoring techniques are available to beekeepers and include sticky inserts placed beneath a mesh floor; ether role test, alcohol wash, drone brood examination and one which has been extensively promoted in recent years, the sugar shake method. This regular estimation of the mite population in a colony is strongly recommended and once a mite load in a colony reaches the damaging threshold levels, a wide variety of control methods can be implemented. These control methods vary from physically removing mites from the colony to the use of hard chemical insecticides.
Genetic control is also crucial to the development of an effective IPM programme. This involves the development of or selection of pest resistant stock. The Russian Honeybee Breeding Program, led by USDA/ARS bee scientist Thomas Rinderer in 1997 was possibly one of the first of breeding programme to breed Varroa resistant stock, but today in many countries, including Ireland, selective breeding programmes are vibrant.
Mite trapping and brood interruption are also both effective means of removing mites physically from the colony. Techniques which physically remove mites from the colony include sticky boards placed beneath the brood box, open mesh floors and sugar dusting. Drone brood removal and the interruption of the brood cycle via queen caging also allows large number of mites to be trapped and subsequently removed. Since 2003 as part of the National Apiculture Programme (NAP) many of these techniques have been tested under Irish conditions. This programme is being co-ordinated by the University of Limerick and is co-funded by EU and DAFM. Open mesh floors were found to reduce mite load in the colonies but not significantly, while drone brood removal significantly reduced mite population, (Coffey, 2007). Presently, as part of 2016-2019 NAP a field trial is ongoing in the research apiary in Teagasc Oakpark which aims to assess the efficacy of seasonal brood interruptions as a Varroa control method. This is part of the COLOSS international study and details of this study can be found on the COLOSS Varroa Taskforce webpage.
Biological control of Varroa focuses primarily on insect pathogenic fungi. The literature shows that several insect parasitic fungi are able to infect and kill Varroa without being a threat to honey bees. A number of commercial products based on the fungi Metarhizium anisopliae and Lecanicillium lecanii have been developed, but in general have proven in effective against Varroa, at least in their current formulation. Therefore, for the control of Varroa, fungi that work under bee hive circumstances, that is high temperature and low humidity are necessary if they are to be effective against Varroa.
Finally, synthetic pesticides play an important role in the management of the Varroa mite. They are a very diverse group and include organic acid (formic acid and oxalic acid) based products, products derived from plant chemicals or essential oils (predominantly thymol) and finally chemical based products for example pyrethroids and organophosphates. Commercially available organic acid based products authorised for use in Ireland include Mite Away Quick Strips (MAQS: active ingredient: formic acid), VarroMed (active ingredients: oxalic acid and formic acid) and ApiBioxal (oxalic acid). According to data from the NAP, under Irish conditions the mean efficacy of MAQS is approximately 70% (Coffey and Breen, in prep), while the field trial on the efficacy of VarroMed is presently ongoing as part of the 2016-2019 NAP. With regards essential oil based products, numerous thymol based products are available commercially and include Apiguard. However, in Ireland, only Apiguard is authorised. Under Irish conditions Apiguard has a mean efficacy of approximately 85% with high colony variability (Coffey, 2007; Coffey and Breen, 2015). Therefore, considering the varroacides authorised in Ireland and their efficacy under Irish conditions, a mean efficacy of greater than 90% can be achieved by administering Apiguard as Autumn treatment (after the honey harvest) followed by ApiBioxal (vaporiser method ) as a winter treatment (Coffey and Breen, 2016). However it should be noted that with the recent authorisation of ApiVar, beekeepers could also achieve an efficacy of greater than 90% with this product as a sole treatment, assuming that the Varroa mite population in Ireland are susceptible to the active ingredient, Amitraz. However, this had not been assessed.
Although, the latter option may appear the simpler approach to Varroa control, it may not be the best approach. Instead beekeepers should aim to forsake the “pesticide threadmill” and embrace the numerous management methods which are an integral part of any integrated approach. Hard chemicals should only be used when and where mite populations exceed threshold numbers. Such an approach will best serve not only beekeepers but also the bee colonies themselves.
References
Coffey, MF (2007) Biotechnical methods in colony management and the use of Apiguard® and ExomiteTM Apis for the control of the Varroa mite (Varroa destructor Oud) in the Irish honeybee (Apis mellifera L.) Journal of Apicultural Research and Bee World 46(4): 213– 219
Coffey M.F. and Breen, J. (2013). Efficacy of Apilife Var® and Thymovar® against Varroa destructor as an Autumn treatment in a cool climate. Journal Apiculture Research 52(5) 210 – 218
Coffey, MF. and Breen., J. (2015). Efficacy of Apiguard ® and Bayvarol ® as sole treatments or as integrated control strategies 70: 227-231
Coffey M.F. and Breen, J. (2016) Efficacy and tolerability of Api Bioxal, as a winter varroacide in a cool temperate climate Journal of Apiculture Research 55: 65-73.
