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

Abstract

Despite the implementation of control strategies, the invasive parasitic mite Varroa destructor remains one of the principal causes of honey bee (Apis mellifera) colony losses in numerous countries. For this reason, the parasite represents a serious threat to beekeeping and to agro-ecosystems that benefit from the pollination services provided by honey bees. Numerous selection programmes have been initiated over the last three decades with the aim of promoting the establishment of balance in the host&amp;ndash;parasite relationship and, thus, helping European honey bees to survive in the presence of the parasite without the need for acaricide treatments. Such programmes have focused on either selective breeding for putative resistance traits or natural selection. To date, no clear overview of these attempts has been available, which has prevented building on past successes or failures and, therefore, hindered the development of a sustainable strategy for solving the V. destructor problem. In the present study, we review past and current selection strategies, report on their outcomes and discuss their limitations. Based on this state-of-the-art knowledge, we propose a strategy for increasing response to selection and colony survival against V. destructor infestations. Developing in-depth knowledge regarding the selected traits, optimising selection programmes and communicating their outcomes are all crucial to our efforts to establish a balanced relationship between the invasive parasite and its new host.

Descriptive Analysis of the Varroa Non-Reproduction Trait in Honey Bee Colonies and Association with Other Traits Related to Varroa Resistance

“…Evaluation at the end of August can thus be influenced by the low proportion of brood in the colony versus stored honey (Tison et al, personal communication). Furthermore, resistance traits can be biased by the horizontal transmission of varroa mites by the drifting of bees or the robbing of hives [59][60][61], especially if the amount of transferred mites differs between colonies of the same apiary [16]. Additionally, colony and mite dynamics are highly changing through time and may influence mite reproduction and therefore MNR results.…”

“…The selection and conservation of these colonies is, however, time consuming and a difficult task. To date, the success of breeding programs worldwide is low [16] and the commercial availability of resistant honey bee stock is rare. This is partly due to the difficulty of unambiguously identifying and understanding the resistant traits before being able to use them in dedicated selection programs.…”

Descriptive Analysis of the Varroa Non-reproduction Trait in Honey Bee Colonies and Association with Other Traits Related to Varroa Resistance

“…The selection and conservation of these colonies is however still time consuming and a difficult task. To date the success of breeding programs worldwide is low [16] and the commercial availability of resistant honey bee stock is rare. This is partly due to the difficulty to unambiguously identify and understand the resistant traits before being able to use them in dedicated selection programs.…”

<em>Varroa destructor</em>: A Complex Parasite, Crippling Honey bees Worldwide

“…No other pathogen or parasite has had a comparable impact on honey bees, in part because varroa only recently adapted from its original host, the Asian honey bee (A. cerana) (Figure 3) to exploit a naïve host with inadequate innate defenses. Varroa incurs only limited damage to A. cerana colonies due to several host defense mechanisms that impact varroa reproduction: mite infertility in worker brood, entombment of drone brood infested with multiple mites, and increased hygienic behavior (reviewed in [4]). The recently re-updated varroa genome (GCA_002443255.1) [5] will be a powerful tool to help understand varroa evolution in response to honey bee novel defenses traits, host-switching, and successful global invasion.…”