Tuesday, November 3, 2015

Are honeybees killing wild bees?

I'm sure you've heard that our pollinators are in trouble. Whether it's birds, bees, or butterflies, the development and destruction of natural habitat is causing big problems. Honeybees have hogged a lot of the attention, partly because of the mysterious cause(s) of colony collapse disorder, but also because of the importance of honeybees to industrialized food production. However, a recent review published in the International Journal for Parasitology highlights the harm that managed bees can inflict on our native bee populations, especially when they carry disease.

Native pollinators include more than just bees.
Illustration from the Pollinator Partnership.

The industrial use of honeybees is one of the main contributors to honeybee decline in recent years.  Pesticides are thought to be a main cause, with compromised health being observed even at sublethal doses. Poor management practices and long-distance transportation cause additional stress and enhance the spread of parasites and disease between colonies. The reliance of managed bees on single food sources (crops) may also pose a problem since it seems that bees can use other plants to help combat certain infections.

In Europe, where honeybees are native, the diseases of domestic populations have been observed to "spillover" into natural populations. Pathogens include parasitic mites, fungi, and a variety of viruses, and are thought to have contributed to the the decline in feral honeybee colonies across the US and Europe. In the UK, the Varroa is thought to have caused the extinction of naturally wild honeybees, with only managed and escaped domestic bees remaining.

Varoa mites are one of the biggest threats to honeybee health

Although honeybees aren't native to North America, managed bees still present a risk to other native bees. Both managed and feral hives can compete with wild bees for food resources. Now we know that they can also transmit disease. There are several documented cases of spillover from honeybees to bumblebees, which are in decline across North America. So it stands to reason that diseases could affect other native pollinators too.

The spread of disease is a major concern given the already poor condition of wild pollinator populations. In fact, along with habitat destruction, pollution, and invasive species, emerging infectious diseases are one of the top contributors to species extinction.

Although it can be difficult to pinpoint the exact cause of disease outbreaks, the introduction of foreign pathogens is certainly a vital component. Also, as in honeybees, stress can also increase the chances of wild bees acquiring and succumbing to disease. Pesticides are one important factor in inducing stress, and a recent study found that bumblebees and solitary bees may be more susceptible to pesticides than honeybees. To make matters worse, bumblebees are also managed and seem to be spreading their ailments to wild bees.

Native wildflowers to support native bees.
Illustration from Native Plants and Wildlife Gardens.

To support wild pollinator populations, be sure to landscape with lots of bee-friendly plants. Because bees can use plant resources to protect themselves from pathogens, maintaining native plant diversity can help keep them healthy. You can also provide them with shelters, like this bee house below. For about native pollinators, check out the Xerces Society website and keep following beeNinja!

Photo borrowed from Zeebeeman's blog

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