Recapping and mite removal behaviour in Cuba: home to the world’s largest population of Varroa-resistant European honeybees

Abstract

The Varroa destructor ectoparasitic mite has spread globally and in conjunction with Deformed Wing Virus has killed millions of honeybee ( Apis mellifera ) colonies. This has forced Northern hemisphere beekeepers into using miticides to avoid mass colony losses. However, in many Southern hemisphere countries widespread treatment did not occur since miticides were prohibitively expensive, or a centralised choice was made not to treat, both allowing natural selection to act. The Varroa mite initially caused high losses before mite-resistance appeared in the honeybee populations. Initially, mite-resistance was only associated with African and Africanised honeybees. Although recently, several isolated mite-resistant European honeybee populations have appeared. Here we studied the mite-resistance in Cuba and found high rates of recapping of infested worker cells (77%), high removal of mites (80%) and corresponding low mite fertility ( r = 0.77). These are all traits found in all naturally evolved Varroa-resistant populations. We can confirm Cuba has the world’s largest European mite-resistant population with 220,000 colonies that have been treatment-free for over two decades and illustrating the power of natural selection. Cuban honeybees are also highly productive, 40–70 kg of honey produced annually, and are mild mannered. Cuba is an excellent example of what is possible when honeybees are allowed to adapt naturally to Varroa with minimal human interference.

Varroa resistance in Apis cerana: a review

“…Resistance developed fairly quickly in these areas, and this is thought to be because of the lack of chemical control and the more naturalised bee keeping style (Grindrod and Martin 2021). Indeed, this is also true of European honey bees in Cuba, a country which is believed to contain the largest population of resistant European honey bees (Luis et al 2022). However, resistance has begun to be observed in Europe and the USA (Oddie et al 2018;Martin et al 2019;Hawkins and Martin 2021;Grindrod and Martin 2021).…”

Virus infections in honeybee colonies naturally surviving ectoparasitic mite vectors

“…The central mechanism seems to be a control of the viral vector, V. destructor. However, traits fostering the ability to survive mite infestations may render colonies more susceptible to other threats: The cell recapping behaviour seems to be involved in suppressing mite reproduction [21] and is present in all tested mite-surviving bee populations [9,15,36], but opening of brood cells may result in a higher susceptibility to other pathogens, such as BQCV.…”

“…This further suggests that adaptations to V. destructor may render colonies more vulnerable to other pathogens. Such a trade-off scenario seems likely, as higher levels of cell recapping in mite-surviving populations [8][9][10][11][12][13][14][15] increases exposure risk to the more vulnerable brood.…”

“…Due to the limited defence mechanisms of Western honeybees, unhindered V. destructor population growth can cause numbers to reach fatal levels in late summer and autumn in temperate climates, when the bees being reared are required for winter colony hibernation [4,6]. There is now very solid evidence that Western honeybee populations, if left untreated, have the potential to adapt to V. destructor infestations without the need for human-mediated mite control [7][8][9] (via large initial colony losses), and that they can develop this ability in as little as five years [10]. Previous literature has pointed to several mechanisms such as reduced post-capping period [10], potential changes in brood volatiles [11], grooming [12], brood removal [13,14] and brood cell recapping [15].…”

“…One of the most prominent traits that has been detected in naturally surviving honeybees, regardless of the mechanisms identified, is suppressed mite reproduction (SMR) [7,16], signified by lower average reproductive output per foundress mite. SMR has been recorded not only in Africanized bee populations surviving V. destructor [9,17], but in the "more susceptible" European populations as well, including the Primorsky bees from Russia [18], the Gotland bees in Sweden, the Avignon bees in France [16,19], in England, Cuba [9] and a population in the Oslo region of Norway [8].…”