Bumblebees

ChiloquinNews article 7/18/2011

I am feeling quite concerned about bumblebees. Usually by the time my creeping thyme flowers, there are dozens of bumblebees, of several species, buzzing about all over it. But not this year.

 Bumblebees rely on a queen to start the colony. It is only the queens that survive the winter. In spring, the huge bumblebees that you see are the queens, looking for a nesting site. They buzz about as though searching and ignore the flowers. They ARE searching. Abandoned rodent holes are a favorite but they’ll take a hole in a tree or even the space under a clump of grass. Once the queen has found a place to call home she builds a few brood cells from wax. She has to gather the pollen and make the nectar to fill the brood cells, and lay the eggs.  She provides food gradually, adding it to the brood cells as the larvae need it rather than leaving all the food in the cell before laying the egg. Like birds, queen bumblebees brood their eggs to keep them warm. Bumblebees are very hairy, but the underside of the abdomen has a bare patch, and so the heat from the queen’s body can pass directly to the clump of wax-covered eggs. During this stage the queen rarely leaves the eggs for long and she keeps them at about 86F. In the early days of the nest it is estimated that a queen may have to visit as many as 6000 flowers per day in order to get enough nectar to maintain the heat needed to brood her eggs. And during every foraging trip the brood will cool down, so the trips must be short.

 It takes about a month for her to raise her first brood. After 4 days or so as an egg, about half the time is spent as a larva feeding, then the rest of the time is spent as a pupa in a cocoon. When they emerge, these bees become workers and help the queen to gather pollen and nectar, and care for the growing number of brood cells, as the queen continues to lay eggs throughout the summer. Bumblebees do make a small amount of honey – just enough to feed the larvae and themselves for a couple of days during bad weather.  Generally, there will be a few dozen bees in any nest, but there can be as many as a couple of hundred. The workers only live for about a month.

 The first brood bees are very small, but each successive brood is a little larger, until the bees are quite big by the end of the season, when the queen will stop producing workers, and lay unfertilized eggs that will develop into males. New queens are just normal worker larvae that receive extra food. The new queens emerge and mate with the drones, then as cold weather sets in, all except the new queens die off.

 Bumblebees are important pollinators. Because they are active from early spring until late fall, they need to forage on many types of flowers, and do not rely on any one flower. However some plants do rely on bumblebees. They perform a behavior called “buzz pollination” where the bee grabs the anther in her jaws and vibrates, causing pollen to fall that would have otherwise remained trapped. Some plants require buzz pollination.

 Just a couple of weeks ago I saw huge bumblebees – queens – gathering pollen, and just today saw tiny bumblebees. This means that as late as July, some of the queens still hadn’t raised their first brood, and here we are in mid-July with only the first brood out gathering pollen. Unless we get a very mild fall, there will not be time for the queens to raise more than just a few broods. I’ve only seen 2 species too, rather than the 4 or 5 species I saw last year.

 In the late 1990′s, bee biologists started to notice a decline in the abundance and distribution of several wild bumblebee species. One of these, native to south-west Oregon may now be extinct. The rapid decline in wild populations occurred at about the time that a disease outbreak was reported in populations of commercially raised western bumblebees, which were distributed for greenhouse pollination in western North America. The timing of this suggests that an escaped exotic disease organism may be the cause of this widespread loss.

Three bumblebee species in my Chiloquin garden, 2009

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