'Pathogen spillover' may be to blame for bee crisis

The mysterious decline of the bumble bee population in North America, which threatens a host of crops used to make food ingredients, could be caused by a virus passed on to wild bumble bees by commercially reared bumble bees, according to scientists.

Researchers at the University of Toronto said there was "circumstantial evidence [suggesting] that pathogen 'spillover' from commercially reared bumble bees, which are used extensively to pollinate greenhouse crops, is a possible cause."

The pathogen in question is one found in commercial bees, and known as Crithidia bombi. The researchers modelled spillover of the pathogen into the wild and concluded that "during the first three months of spillover, transmission from commercial hives would infect up to 20% of wild bumble bees within 2km of the greenhouse."

They added: "However, a travelling wave of disease is predicted to form suddenly, infecting up to 35-100% of wild bumble bees, and spread away from the greenhouse at a rate of 2km a week.

"Given the available evidence, it is likely that pathogen spillover from commercial bees is contributing to the ongoing decline of wild bumble beesin North America. Improved management of domestic bees, for example by reducing their parasite loads and their overlap with wild congeners, could diminish or even eliminate pathogen spillover."

The Toronto research represents another step towards solving a problem that is causing major concern among beekeepers, the food industry and politicians worldwide.

Bumble bees are important pollinators of many food crops such as tomatoes, peppers, soft berry fruit and top fruit. Their cousins the honey bees, also important for pollination of crops, are in decline, too. A quarter of their population is estimated to have vanished from the US in recent years, for example, partly as a result of the mysterious Colony Collapse Disorder, where bees desert the hive and die.

Money is being ploughed into research. Earlier this year, ice cream manufacturer Haagen Dasz launched a campaign called Haagen Dasz Loves Honey Bees. It promised researchers in the US $250,000 to look into the decline of the bee population, funded by sales of a special edition ice cream flavour called Vanilla Honey Bee.

The company is concerned that supply of ingredients such as almonds, cherries, strawberries and raspberries could be hit if sufficient crops cannot be pollinated. Some 40% of the ice cream flavours it uses are dependent on honey bee pollination.

The US government has also pledged $4 million in funding in July to the University of Georgia to study the causes of CCD. But is this enough? Not according to Denver beekeeper Tom Theobold. "Move the decimal place about three places, and that gives you an idea of what this means in terms of the magnitude of the crisis," he told Functional Ingredients.

"And I don't mean to sound ungrateful. $4 million is a lot of money, and I'm sure that the University of Georgia can put it to good use. But this problem has been developing for years. Those of us who have been paying attention to these things have warned repeatedly over the last ten years that we are headed for crisis.

"Research has been a big problem in that there's been relatively little research money invested in the beekeeping industry. I'm not one of those people who thinks the government should solve all of our problems; I'm just the opposite really. But because of the nature of the business and the small number of people involved, and the critical nature of the pollination connection, it's the kind of thing you have to expect government to support for the benefit of everybody. Here, in this country, and in most countries that have agribusiness, the bees are responsible almost exclusively for the pollination of between 90 and 130 food crops."

For now, however, Theobold and his colleagues in the beekeeping industry will have to content themselves with what research there is. And it is, at least, a subject that appears to be catching academics' imaginations.

Scientists in the UK, for instance, have taken an unusual step to tackle the problem on their shores. A springer spaniel named Toby has been trained to seek out bee nests as part of a £112,000 study into the decline in bee populations. There used to be 25 different species of bumblebee in the UK. Three are extinct and up to seven more are close to extinction.

"If we are going to conserve them, we need to know more about them, where they live, what causes the nests to die," Professor Dave Goulson of Stirling University told The Guardian newspaper. "The last few years have been really bad for bumblebees. We think it's probably the weather, but we don't know. We need to know how many nests there are. We need to find the nests to know how long they live and what destroys them."

The fate that awaits us all if the decline in bee populations continues over the long term is illustrated plainly in a book on the subject of the crisis, A World Without Bees, by Alison Benjamin and Brian McCallum. This tells how every April thousands of families in southern Sichaun in China gather to pollinate fruit trees manually because over-use of pesticides killed off all the bees in the region 20 years ago.

The book explains: "The farmers must first collect pollen from the trees by scrubbing it off the anthers, the male part of the flowers, into a bowl. They let it dry for two days, before the whole family comes out with their homemade feather dusters [made from bamboo sticks and chicken feathers], which are dipped in the pollen and applied to the flowers' stigmas, or female parts."

Ingenious as this is, it isn't a practical solution to the crisis, according to Theobold. "It can be done," he said, "but it certainly can't be done on a commercial scale across the US to produce food for 300 million people."

Does Pathogen Spillover from Commercially Reared Bumble Bees Threaten Wild Pollinators?
Michael C. Otterstatter*, James D. Thomson
Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada

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