July 23, 2009

Honeybees Use Resin To Sterilize Hives

Scientists have discovered that honeybees sterilize their hives with antimicrobial resin to protect their overall health, BBC News reported.

Experts say this gives the whole colony a form of "social immunity", which lessens the need for a strong immune system in each individual bee.

A team of scientists wrote in the journal Evolution that while honeybee resin is known to kill a range of pathogens, it is the first time that bees themselves have been shown to utilize its properties.

Wild honeybees typically nest in tree cavities, and when founding a new colony they line the entire nest interior with propolis, a thin layer of resins that they mix with wax.

Propolis is also used to smooth surfaces in the hive, close holes or cracks in the nest, reduce the size of the entrances to keep out intruders, and to embalm intruders killed in the hive that are too large to push out.

In relation to human health, a number of studies have shown that propolis has a range of antimicrobial properties that are effective against viruses, bacteria and even cancer cells.

Mike Simone, a PhD student from the University of Minnesota in St Paul, and his supervisor Professor Marla Spivak, tested the effectiveness of honeybee propolis against the HIV-1 virus.

They then progressed to see how it impacted bee pathogens, such as American foulbrood.

Simone said it lead them to wonder what other things propolis might be doing for the bees.

The team then painted the inside walls of hives with an extract of propolis collected from Brazil or Minnesota, which mimicked how propolis or resins would be distributed in a feral colony nesting in a hollow tree.

New honeybee colonies that were housed either in hives enriched with resin, or hives without the resin layer, were created to act as a control.

The team then collected bees that had been born in each colony after one week of exposure, where genetic tests on the 7-day-old bees showed that those growing in the resin-rich colonies had less active immune systems.

Simone said the resins likely inhibited bacterial growth, which meant the bees did not have to activate their immune systems as much.

"Our finding that propolis in the nest allows bees to invest less in their immune systems after such a short exposure was surprising. Resins in the hive have been thought of as a potential benefit to a honey bee colony, but this has never been tested directly," she said.

The researchers concluded that using resins to help sterilize the colony could be thought of as a type of "social immunity," which may partly explain why bees and other social insects, such as ants, collect resins to build their nests.

Simone said that honeybees use wax, which they produce themselves, to do all the things that they use resin for in the nest.

"So it is interesting to think about why they might go and collect resins. Especially since resins, being sticky, are hard to manipulate and take a lot of energy for individual bees to gather in very small quantities," she said.

Previous studies suggest that some mammals and birds coat themselves in naturally occurring plant resin in a bid to reduce certain parasite infestations.


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