Although it is much smaller than the honeybee, the small hive beetle is a huge threat. Photo: Bram Cornelissen
You may not realise it, but every third bite of food we have is thanks to the honeybee. However, the small hive beetle may throw a spanner in the works: the parasite is a growing threat to the pollinator. A PCR test developed in Wageningen should help to prevent the spread of the beetle.
Western honeybees are crucial for food production. In the Netherlands they are by far the most important pollinators for crops such as apples, blueberries, pumpkins, rapeseed and sunflower. “Pollination is to plants what sex is to people: essential for reproduction. What’s more, it’s important for the entire ecosystem, because pollination ensures genetic variation in plants,” says Delphine Panziera, a bee biologist at Wageningen University & Research. Honeybees play a key role in this. The vast majority of wild plants are pollinated by honeybees, because they outnumber all other pollinating insects.
Shift due to climate change
But climate change threatens the continued existence of honeybees. Researches are seeing the arrival of more parasites and pathogens that are a danger to the honeybee. This is because it is getting warmer on average in temperate zones. Normally, honeybees produce eggs between March and October; there is no brood in the winter. This means that parasites that live on bee broods usually do not survive the cold period. “But the winter of 2020 wasn’t cold enough, for example, so there was a bee brood in the beehives between Christmas and New Year. That’s potentially a big problem because some parasites feed on the brood of honeybees, which means the parasites may be able to develop and multiply.”
The eggs that the beetle lays in beehives grow into larvae, which eat everything that is available in the hive. Photo: Bram Cornelissen
A parasite that has appeared further and further north in the last while is the small hive beetle. This match-head-sized beetle originates from southern Africa. However, since the beginning of this century the beetle has spread over large parts of the United States, Canada, Mexico and Egypt. So far, in Europe the parasite has only been spotted in southern Italy. In 2014, small hive beetles were found in more than 50 different locations in Apulia and Calabria.
The Italian government has designated quarantine areas. “This means that the beekeepers in an area where the beetle has been spotted are not allowed to move their hives outside that area and that it is prohibited to trade out bees and bee products,” says Panziera.
It is in fact not the small hive beetle itself that is harmful to honeybees – it is the eggs that the beetle lays inside the beehive. The eggs grow into larvae, which eat everything that is available in the hive: bee brood, honey and even beeswax. The nest of an entire bee colony can be destroyed in no time. In addition, the larval droppings cause the honey to ferment in the hive and become unusable as a food source for the bees. The result is that the bee colony eventually dies.
So far, in Europe the parasite has only been spotted in southern Italy
The small hive beetle may be as small as the size of a match head, but its impact can be ginormous; the spread of this parasite could threaten honeybee populations and global food production. A PCR-like test to detect the small hive beetle should help prevent this from happening. Delphine Panziera, researcher at Wageningen University & Research, explains why their newly developed method is so important. (UK subtitles available in video)
Pollination is important for the entire ecosystem
The larvae then pupate into beetles. This happens in the soil underneath the beehive. The mature larvae drop out of the hive and burrow into the ground. Research by former WUR researcher Bram Cornelissen shows that as the northern hemisphere becomes warmer and soil temperatures rise, there is a greater chance that the larvae can survive and pupate.
Impact will increase
According to Wageningen research, the arrival of the hive beetle will have a uncertain effect for Dutch beekeeping. Another invasive species, the varroa mite, is many times more dangerous. But climate change will make the impact of the small hive beetle increase, so it is important to keep an eye on the little parasite. A test developed in Wageningen may help.
Every country in the European Union has a reference laboratory for notifiable diseases in honeybees, which includes the small hive beetle. “The current official detection method is visual detection, but there is a good chance that a beetle will be missed in a hive with 50,000 bees.” According to Panziera, who, in addition to being a bee biologist at WUR, is also head of the National Reference Laboratory for notifiable diseases for honeybees, the method is very labour-intensive and it takes a while before all hives in a suspect area have been checked. “And by the time all the hives in an area five kilometres across have been checked, the beetle may have already spread further to a much larger area.”
It is not the small hive beetle itself that is harmful to honeybees, but the larvae. Photo: Bram Cornelissen.
Samples are analysed in Wageningen for the presence of the DNA of the small hive beetle, to find out whether it is present in the hives. Photo: Bram Cornelissen
The test developed in Wageningen is comparable to the well-known Covid self-test. Narrow spaces inside of the hive — areas that bees cannot reach, but the much smaller parasite can — are brushed with a cotton swab. The sample is then analysed for the presence of parasite DNA, in the same way as with the PCR test for Covid. The result can be known within 24 hours. An isolated field trial showed that the PCR test can detect a single parasite in a hive with a colony of 50,000 bees.
Attached to the hive and vulnerable
But it’s not just the invasive parasites that worry the bee biologist. Western honeybees are much less resilient to pests and diseases than they used to be. “Beekeepers don’t like aggressive bees or bees that swarm. That’s why they select colonies that swarm less and are easy to handle. As a result, the generic diversity of Western honeybees has declined over the past decades. This increases the vulnerability to parasites such as the small hive beetle.” Just for the record: the small hive beetle has not yet been found in the Netherlands. But that doesn’t mean we shouldn’t be vigilant, according to Panziera. “Suppose your neighbour has gone camping in Calabria and comes back after two weeks with a few parasites in his backpack. Unintentionally. Before you know it, the beetles have found a hive.”
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