Researchers demonstrate chemical-free solutions against harmful mites: "Chemicals have been a safety net"

Beekeepers have been using chemical control methods for decades to keep the varroa mite in check, but this has not solved the problem – on the contrary, it has only prolonged it. This explains senior researcher Per Kryger from the Department of Agroecology at Aarhus University, who is one of the authors of two new reports presenting two chemical-free methods to combat the mite. The varroa mite is a small parasite that, since reaching Denmark in 1984, has spread to almost all Danish bee colonies. The mite weakens the bee directly, but the greatest danger is that it spreads viruses, which are the most common cause of death during winter. The two previous winters saw between 20 and 25 percent of Danish bee colonies die, estimates Per Kryger. "Chemicals have been a safety net. People think: 'We have control over this, we just give them a little chemical,' and then they don't think about it anymore. But it doesn't solve the problem – it prolongs it," he says in a press release. Additionally, there are currently no approved control agents available on the Danish market. Beekeepers who obtain medicine from other EU countries must ensure they have a Danish package leaflet and use it correctly. Handbooks for beekeepers This is the background for the two new dissemination reports published simultaneously by DCA – the National Centre for Food and Agriculture: 'Targeted Breeding of Resilient Bees' and 'Brood Pause – an Integrated Element in Better Beekeeping Practices.' The reports are intended as handbooks for Danish beekeepers and are written by Per Kryger and Annette Bruun Jensen. The first report focuses on breeding. As early as 1937, American researcher Orlando Park proved that some bee colonies could survive deadly American foulbrood because the bees actively removed diseased brood from the brood cells – what we today call hygienic behavior. Danish beekeepers have used breeding to combat nosema disease and reduced the proportion of infected samples from 80 to under 20 percent in just five years. The report suggests that the same approach can be used against varroa, but the authors warn against breeding too selectively: too strong selection for varroa resistance can negatively affect traits like docility and honey production. "Variation in itself is not a problem – it is a prerequisite for progress," write Per Kryger and Annette Bruun Jensen in the report. Brood pause breaks the mite's life cycle The second report is based on the fact that the varroa mite can only reproduce in sealed brood cells. Removing brood or preventing the queen from laying eggs for a period directly slows the mite's reproduction. In practice, Danish beekeepers can primarily use two methods: confining the queen for at least 25 days or removing the brood frames entirely from the colony. There is also a biological bonus to this approach compared to chemical methods. "When controlling with chemicals, you also weaken the bees' own immune system. In an experiment, we found that even though the mites were almost eliminated from the colony after treatment in August, there were actually more viruses in the bees afterward – not fewer," says Per Kryger. However, these methods require skill and timing. "We have lost bees ourselves because we weren't skilled enough from the start. I recommend that beekeepers start with a few colonies, learn the technique, and master it before fully implementing it," he says. A new mite is on the way Both reports emphasize that beekeepers should closely monitor mite levels. "We participated in a large EU trial with 1,200 Danish colonies, where we found that the risk of a colony dying increased from 20 to 50 percent if there were more than 10 mites per 100 bees," says Per Kryger. The researchers therefore recommend that beekeepers respond as soon as about three mites per 100 bees are found in a wash sample. According to Kryger, these two methods could become even more important in the coming years. A new and more brood-dependent mite, Tropilaelaps, may be on its way from Asia. "It has reached Georgia, Russia, and Turkey, where there is a lot of migratory beekeeping. Once it crosses into Turkey, it could reach the EU within a year," he says, adding: "The long-term goal is to breed bees that can survive without the use of chemicals at all. Initially, it’s about using less – but in the future, none at all."