Abstract
The honey bee (Apis mellifera) is the most important managed pollinator to sustainable agriculture and our ecosystem. Yet managed honey bee colonies in the United States experience 30–40% losses annually. Among the many biotic stressors, the parasitic mite Varroa destructor is considered one of the main causes of colony losses. Bees’ mite-biting behavior has been selected as a Varroa-tolerant or Varroa-resistant trait in the state of Indiana for more than a decade. A survey of damaged mites from the bottom of a colony can be used as an extended phenotype to evaluate the mite-biting behavior of a colony. In this study, on average, 37% of mites sampled from the breeding stocks of 59 colonies of mite biters in Indiana were damaged or mutilated, which is significantly higher than the 19% of damaged mites found in commercial colonies in the southern United States. Indiana mite biter colonies had a higher proportion of damaged mites, although among the damaged mites, the number of missing legs was not significantly higher. In addition, the morphology of pollen-forager worker bee mandibles was compared by X-ray microcomputed tomography for six parameters in two populations, and a difference was detected in one parameter. Our results provide scientific evidence that potentially explains the defensive mechanism against Varroa mites: structural changes in the worker bee mandibles.
Highlights
Since 1987, when the ectoparasitic mite Varroa destructor was first introduced in the United States, Varroa infestations have become the primary contributors to honey bee (Apis mellifera) colony losses (Guzmán-Novoa et al, 2010; Le Conte et al, 2010; Nazzi and Le Conte, 2016)
The mite-biting or grooming behavior referred to here involves a worker bee using its two forelegs and the two mandibles of its mouthpart to attack a Varroa mite in a colony
We investigated the Varroa mite population and the differences in mite-biting behavior among commercial colonies, mite-biter colonies, and open-mated mite-biter colonies in analysis of variance (ANOVA) suggested that one or more groups were significantly different, F(2,80) = 28.86, p = 4.16e−10
Summary
Since 1987, when the ectoparasitic mite Varroa destructor was first introduced in the United States, Varroa infestations have become the primary contributors to honey bee (Apis mellifera) colony losses (Guzmán-Novoa et al, 2010; Le Conte et al, 2010; Nazzi and Le Conte, 2016). Varroa mites can infest honey bee colonies and cause colony losses as they feed on the fat bodies of bee. The European honey bee (A. mellifera) has developed a set of behavioral defenses against Varroa mites to keep the mite population low, such as grooming, biting, and performing hygienic behaviors (Ruttner and Hänel, 1992; Spivak, 1996; Arechavaleta-Velasco and Guzmán-Novoa, 2001; GuzmanNovoa et al, 2012; Tsuruda et al, 2012; Villa et al, 2017). No report to date has compared changes in the mandibles as a potential mechanism for the mite-biting behavior
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