New research findings are only going to add to beekeepers’ headaches as they grapple with ongoing effects of varroa mite.
Since being discovered in North Island hives in the early 2000s, the debilitating mite has spread throughout New Zealand, requiring constant chemical treatments to avoid devastating losses in hive populations. Its presence in hives cause malformation, weakening of bee health and greater disease risk.
But the latest work by researchers in Germany’s University of Ulm, published in the Royal Society Open Science journal, has found that as debilitating as the invasive mite is on its own, it is also responsible for introducing “hitch hiker” viruses into beehive populations.
The researchers looked at the impact of 14 viruses in hive populations in a global study that included taking samples from NZ hives in the upper South Island, Otago and Auckland region.
Samples were also gathered from hive populations in the British Isles, Scandinavia and Canada.
As expected, the researchers found the presence of varroa in hives dramatically increased the incidence of deformed wing virus, a virus typically closely correlated to varroa’s presence.
But they also found several other viruses have become prevalent, including black queen cell virus, which causes mortality in queen bee pupae, and sacbrood virus, which infects honeybee larvae.
The findings confirmed the scientists’ hypothesis about varroa opening the door to a greater range of viral infections, supported by the wide global correlation in disease levels and varroa infections in the sampled areas.
They also raised the concern that with 20,000 species of wild bees playing critical roles in agriculture and native ecosystems, the honeybees’ infections could likely spillover into those varieties’ populations.
The findings accompany NZ work released last year that found NZ bee populations are developing a unique resistance to varroa treatment chemical flumethrin, not seen elsewhere in the world.
Loss rates in NZ from varroa have been growing at an increasing rate, up 20% last year on 2021, and overall 62% greater than in 2015. Loss rates of 6.5% were reported in 2022.
Beekeepers only have two key chemicals in their arsenal to protect hives against varroa.
Researchers at Manaaki Whenua Landcare Research are hoping that newly developed gene-silencing technology that shuts down certain sequencing in the varroa mite could provide an answer.