Bees Use Propolis to Protect Hive From Pesticide-Contaminated Pollen

Honeybees 'Entomb' Hives to Protect Against Pesticides, Say Scientists By Fiona Harvey, The Guardian (UK), 4/4/11

Honeybees are taking emergency measures to protect their hives from pesticides, in an extraordinary example of the natural world adapting swiftly to our depredations, according to a prominent bee expert.

Scientists have found numerous examples of a new phenomenon – bees "entombing" or sealing up hive cells full of pollen to put them out of use, and protect the rest of the hive from their contents. The pollen stored in the sealed-up cells has been found to contain dramatically higher levels of pesticides and other potentially harmful chemicals than the pollen stored in neighbouring cells, which is used to feed growing young bees.

"This is a novel finding, and very striking. The implication is that the bees are sensing [pesticides] and actually sealing it off. They are recognising that something is wrong with the pollen and encapsulating it," said Jeff Pettis, an entomologist with the US Department of Agriculture. "Bees would not normally seal off pollen."

But the bees' last-ditch efforts to save themselves appear to be unsuccessful – the entombing behaviour is found in many hives that subsequently die off, according to Pettis. "The presence of entombing is the biggest single predictor of colony loss. It's a defence mechanism that has failed." These colonies were likely to already be in trouble, and their death could be attributed to a mix of factors in addition to pesticides, he added.

Bees are also sealing off pollen that contains substances used by beekeepers to control pests such as the varroa mite, another factor in the widespread decline of bee populations. These substances may also be harmful to bees, Pettis said. "Beekeepers - and I am one – need to look at ourselves in the mirror and ask what we are doing," he said. "Certainly [the products] have effects on bees. It's a balancing act – if you do not control the parasite, bees die. If you control the parasite, bees will live but there are side-effects. This has to be managed."…

The entombing phenomenon was first noted in an obscure scientific paper from 2009, but since then scientists have been finding the behaviour more frequently, with the same results.

Bees naturally collect from plants a substance known as propolis, a sort of sticky resin with natural anti-bacterial and anti-fungal qualities. It is used by bees to line the walls of their hives, and to seal off unwanted or dangerous substances – for instance, mice that find their way into hives and die are often found covered in propolis. This is the substance bees are using to entomb the cells…