Use of Chemical and Nonchemical Methods for the Control of Varroa destructor (Acari: Varroidae) and Associated Winter Colony Losses in U.S. Beekeeping Operations

Abstract

The parasitic mite Varroa destructor (Acari: Varroidae) is a major cause of overwintering honey bee (Apis mellifera) colony losses in the United States, suggesting that beekeepers must control Varroa populations to maintain viable colonies. Beekeepers have access to several chemical varroacides and nonchemical practices to control Varroa populations. However, no studies have examined large-scale patterns in Varroa control methods in the United States. Here we used responses from 4 yr of annual surveys of beekeepers representing all regions and operation sizes across the United States to investigate use of Varroa control methods and winter colony losses associated with use of different methods. We focused on seven varroacide products (amitraz, coumaphos, fluvalinate, hop oil, oxalic acid, formic acid, and thymol) and six nonchemical practices (drone brood removal, small-cell comb, screened bottom boards, powdered sugar, mite-resistant bees, and splitting colonies) suggested to aid in Varroa control. We found that nearly all large-scale beekeepers used at least one varroacide, whereas small-scale beekeepers were more likely to use only nonchemical practices or not use any Varroa control. Use of varroacides was consistently associated with the lowest winter losses, with amitraz being associated with lower losses than any other varroacide product. Among nonchemical practices, splitting colonies was associated with the lowest winter losses, although losses associated with sole use of nonchemical practices were high overall. Our results suggest potential control methods that are effective or preferred by beekeepers and should therefore inform experiments that directly test the efficacy of different control methods. This will allow beekeepers to incorporate Varroa control methods into management plans that improve the overwintering success of their colonies.

Varroa destructor: how does it harm Apis mellifera honey bees and what can be done about it?

“…Different approaches are used by beekeepers to control Varroa infestation of their colonies. Synthetic and organic acaricides as well as essential oils provide good results to prevent colony losses and the latter, represent interesting tools for organic beekeeping [75]. Depending on the country, methods may differ due to variations in the laws governing the use of chemicals.…”

“…A provisional solution to limit and temporally bypass Varroa resistance to miticides is to switch between molecules with different molecular targets. Synthetic acaricides could then provide good results for preventing colony losses [75]. Growing data have been published on acaricide residues in honey bee colony matrices, particularly in wax, which have the chemical properties to store the used lipophilic acaricides at concentrations that could even be toxic to the bees [78,87,88].…”

Three Decades of Selecting Honey Bees that Survive Infestations by the Parasitic Mite <em>Varroa destructor</em>: Outcomes, Limitations and Strategy

“…In Northern America, selected populations from the hygienic, VSH and 'Russian' lines may have a better resistance potential and so are used by beekeepers in several regions (Danka et al, 2013b;Rinderer et al, 2010). Survey data have indicated lower colony losses in operations rearing resistant stocks of A. mellifera when compared to operations rearing only nonresistant stocks (Haber et al, 2019). However, high colony losses attributed to V. destructor are still reported in the USA (Kulhanek et al, 2017).…”

Mutations associated with pyrethroid resistance in Varroa mites, a parasite of honey bees, are widespread across the USA

“…Prior to 2006, colony losses in the US were estimated to average 5-10% each year 3 , but they significantly increased to average around 39% annually in the last 10 years BIP, 1 . These losses can be recovered by replacing the colonies, but it has an economic toll and extra management efforts that are estimated to be millions of US dollars per year [3][4][5][6] . These high levels of losses are a concern for US beekeepers, the farmers that relies on beekeepers to provide bees for pollination, and the consumers who benefit from the diversity of food products that honey bee pollination facilitates [6][7][8][9] .…”