Varroa

Abstract: Varroa jacobsoni was first described as a natural ectoparasitic mite of the Eastern honeybee (Apis cerana) throughout Asia. It later switched host to the Western honeybee (A. mellifera) and has now become a serious pest of that bee worldwide. The studies reported here on genotypic, phenotypic and reproductive variation among V. jacobsoni infesting A. cerana throughout Asia demonstrate that V. jacobsoni is a complex of at least two different species. In a new classification V. jacobsoni is here redefined as encompassing nine haplotypes (mites with distinct mtDNA CO-I gene sequences) that infest A. cerana in the Malaysia–Indonesia region. Included is a Java haplotype, specimens of which were used to first describe V. jacobsoni at the beginning of this century. A new name, V. destructor n. sp., is given to six haplotypes that infest A. cerana on mainland Asia. Adult females of V. destructor are significantly larger and less spherical in shape than females of V. jacobsoni and they are also reproductively isolated from females of V. jacobsoni. The taxonomic positions of a further three unique haplotypes that infest A. cerana in the Philippines is uncertain and requires further study. Other studies reported here also show that only two of the 18 different haplotypes concealed within the complex of mites infesting A. cerana have become pests of A. mellifera worldwide. Both belong to V. destructor, and they are not V. jacobsoni. The most common is a Korea haplotype, so-called because it was also found parasitizing A. cerana in South Korea. It was identified on A. mellifera in Europe, the Middle East, Africa, Asia, and the Americas. Less common is a Japan/Thailand haplotype, so-called because it was also found parasitizing A. cerana in Japan and Thailand. It was identified on A. mellifera in Japan, Thailand and the Americas. Our results imply that the findings of past research on V. jacobsoni are applicable mostly to V. destructor. Our results will also influence quarantine protocols for bee mites, and may present new strategies for mite control.

Abstract: Emerging diseases are among the greatest threats to honey bees. Unfortunately, where and when an emerging disease will appear are almost impossible to predict. The arrival of the parasitic Varroa mite into the Hawaiian honey bee population allowed us to investigate changes in the prevalence, load, and strain diversity of honey bee viruses. The mite increased the prevalence of a single viral species, deformed wing virus (DWV), from ~10 to 100% within honey bee populations, which was accompanied by a millionfold increase in viral titer and a massive reduction in DWV diversity, leading to the predominance of a single DWV strain. Therefore, the global spread of Varroa has selected DWV variants that have emerged to allow it to become one of the most widely distributed and contagious insect viruses on the planet.

Abstract: Since 2006, disastrous colony losses have been reported in Europe and North America. The causes of the losses were not readily apparent and have been attributed to overwintering mortalities and to a new phenomenon called Colony Collapse Disorder. Most scientists agree that there is no single explanation for the extensive colony losses but that interactions between different stresses are involved. As the presence of Varroa in each colony places an important pressure on bee health, we here address the question of how Varroa contributes to the recent surge in honey bee colony losses.

Abstract: Varroa mites (Varroa destructor) are ectoparasites of honey bees (Apis mellifera) and cause serious damage to bee colonies. The mechanism of how varroa mites kill honey bees remains unclear. We have addressed the effects of the mites on bee immunity and the replication of a picorna-like virus, the deformed wing virus (DWV). The expression of genes encoding three antimicrobial peptides (abaecin, defensin, and hymenoptaecin) and four immunity-related enzymes (phenol oxidase, glucose dehydrogenase, glucose oxidase, and lysozyme) were used as markers to measure the difference in the immune response. We have demonstrated an example of an ectoparasite immunosuppressing its invertebrate host with the evidence that parasitization significantly suppressed expression of these immunity-related genes. Given that ticks immunosuppress their vertebrate hosts, our finding indicates that immunosuppression of hosts may be a common phenomenon in the interaction and coevolution between ectoparasites and their vertebrate and invertebrate hosts. DWV viral titers were significantly negatively correlated with the expression levels of the immunity-related enzymes. All bees had detectable DWV. Mite-infested pupae developed into adults with either normal or deformed wings. All of the deformed-wing bees were greatly infected by DWV (≈106 times higher than varroa-infested but normal-winged bees). Injection with heat-killed bacteria dramatically promoted DWV titers (105 times in 10 h) in the mite-infested, normal-winged bees to levels similar to those found in mite-infested, deformed-wing bees. Varroa mites may cause the serious demise of honey bees by suppressing bee immunity and by boosting the amplification of DWV in bees exposed to microbes.