Natural selection, selective breeding, and the evolution of resistance of honeybees (Apis mellifera) against Varroa

Abstract

We examine evidence for natural selection resulting in Apis mellifera becoming tolerant or resistant to Varroa mites in different bee populations. We discuss traits implicated in Varroa resistance and how they can be measured. We show that some of the measurements used are ambiguous, as they measure a combination of traits. In addition to behavioural traits, such as removal of infested pupae, grooming to remove mites from bees or larval odours, small colony size, frequent swarming, and smaller brood cell size may also help to reduce reproductive rates of Varroa. Finally, bees may be tolerant of high Varroa infections when they are resistant or tolerant to viruses implicated in colony collapse. We provide evidence that honeybees are an extremely outbreeding species. Mating structure is important for how natural selection operates. Evidence for successful natural selection of resistance traits against Varroa comes from South Africa and from Africanized honeybees in South America. Initially, Varroa was present in high densities and killed about 30% of the colonies, but soon after its spread, numbers per hive decreased and colonies survived without treatment. This shows that natural selection can result in resistance in large panmictic populations when a large proportion of the population survives the initial Varroa invasion. Natural selection in Europe and North America has not resulted in large-scale resistance. Upon arrival of Varroa, the frequency of traits to counter mites and associated viruses in European honey bees was low. This forced beekeepers to protect bees by chemical treatment, hampering natural selection. In a Swedish experiment on natural selection in an isolated mating population, only 7% of the colonies survived, resulting in strong inbreeding. Other experiments with untreated, surviving colonies failed because outbreeding counteracted the effects of selection. If loss of genetic variation is prevented, colony level selection in closed mating populations can proceed more easily, as natural selection is not counteracted by the dispersal of resistance genes. In large panmictic populations, selective breeding can be used to increase the level of resistance to a threshold level at which natural selection can be expected to take over.

Quantitation of neuroxin-1, ataxin-3 and atlastin genes related to grooming behavior in five races of honey bee, Apis mellifera L., 1758 (Hymenoptera: Apidae), in Turkey

“…Grooming behavior in response to Varroa mites is also associated with injured mites falling from bees in colonies (Arechavaleta-Velasco & Guzman-Novoa, 2001) and the rate of damaged mites per hive varies according to the honey bee race. Van Alphen & Fernhout (2020) reported Italian race had an average of about 6% mite damage. In contrast, Rosenkranz et al (1997) recorded an average of 45% mite damage in Italian and Carniolan bees, while Africanized A. mellifera damaged 39%.…”

Varroa destructor from the Laboratory to the Field: Control, Biocontrol and IPM Perspectives—A Review

“…It is a different story with A. mellifera so far where the co-evolution is shorter than A. cerana . Nevertheless, several traits such as varroa sensitive hygiene (VSH) or suppressed mite reproduction (SMR) emerged and are still broadly studied [ 167 , 168 , 169 ]. In the meantime, chemical solutions were used to face this invader.…”

Frontiers in effective control of problem parasites in beekeeping

“… Berry et al (2022) demonstrated how regular and repeated treatment with oxalic acid vapour while significant capped brood area is present in the colony may work as a prophylactic approach, preventing varroa population growth, however is not capable of reducing varroa populations once they pass some treatment threshold as would be used in a IPM framework. Of note however is the significant IPM-conforming investment and emphasis on breeding bees which are mite-resistant; this is a topic which has been recently reviewed in detail by numerous authors ( Guichard et al, 2020 ; Le Conte et al, 2020 ; Mondet et al, 2020 ; Noël et al, 2020 ; Spivak and Danka, 2020 ; van Alphen and Fernhout, 2020 ). Alt-text: Box 1

Tracking Failures Negative results are underreported broadly in science; in applied sciences, this presents as a problem when ineffective treatments are not sufficiently and widely reported as inadequate.

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