Thursday, August 30, 2012

Farm Bulletin: A Queen with a Pearl Collar

When one thinks of the residents of a farm, humans undoubtedly come first to mind. But other inhabitants, like animals, birds and insects, must also be counted, particularly when the farm uses organic methods. Few, though, are as critically important as the humble bumblebee. Contributor Anthony Boutard of Ayers Creek Farm sings its praises.

It is late summer and, as usual, members of Hymenoptera—the insect order that groups together the wasps, bees and ants—are putting on a show. About two weeks ago, a large cohort of male bumblebees emerged. Fidgety and playfully pugnacious, they fly about just inches above the ground, darting here and there, trying to stay out of reach of any remaining barn swallows seeking a quick snack on the way to Capistrano. Their shape, coloration and behavior is very different from the females of the colony—the queen and her daughters, the workers. The males do not have a stinger.

The male bumblebee develops from an unfertilized egg. In other words, denied sperm, an egg paradoxically yields a male. Fatherless male offspring is one of those peculiar twists that makes the Hymenoptera so interesting. Both the queen and her sisters can produce eggs, but only the queen has mated and produces fertilized eggs which develop into the females of the nest. The sperm from her nuptial flights is held in a special organ, and the eggs are fertilized as they are laid, or not in the case of males. Typically, the males appear toward the end of the colony's existence and may have hatched from an egg laid by either the queen or one of her daughters.

Despite their aimless flight pattern and endless tousling with their brethren, the males are ever alert for the emergence of a newly hatched queen, or gyne as entomologists call her, and the opportunity to mate with her. (Photo at top shows a Brown-belted bumblebee queen or gyne emerging from the nest hole.) Apparently, the males identify her by sight, not a chemical cue, which may explain why a hapless swallow-tail passing through earlier this week found itself mobbed by amorous bumblebees. Discovering this lek of bees, we shared with the males a keen interest in seeing the queens emerge, pausing to survey the area as we passed at various times during the day. The nest is in an old mouse hole in the heavily traveled lane between the blackberry fields. Monday the show began.

The new queens are genetically the same as the worker sorority; there is no special queen gene. They are raised in larger wax vessels than the workers, and they are fed more food during the larval stage. In order to survive the winter and a summer of laying eggs, a more robust body is needed. After emerging from their pupae, these large females linger in the nest and fatten up for a few days. They emerge from the nest, mostly individually, groom themselves and then take flight. In seconds, the males converge upon her and, in an airborne scrum, try to do the honors. Once a coupling occurs, the surplus males drift back to their posts and the job is finished on the ground. After mating, the queen quickly seeks shelter. She mates more than once and, well-provisioned with sperm, she will spend some time building her fat reserves for the winter hibernation. If all goes well, she will emerge from her hibernation lair in the spring and start a new colony.

We have at least four bumblebee species on the farm: the white-shouldered, black-tailed, yellow-faced and the brown-belted—the latter are the queens emerging this week. The scientific name is Bombus griseocollis and translates into "bumblebee with a pearl-grey neck," probably referring to a fine line of hairs that encircle the neckline of the females. The brown belt of the English name refers to a distinct band of brown hairs on the second abdominal section of the males, just behind the wings. (Photo at left, above, shows a Brown-belted bumblebee, Bombus griseocollis, male drone waiting for his gyne.) The newly emerged gyne is very beautiful. Her coat is much lighter than the male's or worker's. Interestingly, the male brown-belted bumblebees darting about are not merely callow Lotharios; it is one of four bumblebee species where the males actually assist in the nest by incubating the brood, an important task.

The bumblebees can be difficult to identify, prompting one entomologist to call them "morphologically monotonous." The key distinguishing characteristic are differences in the male genitalia, perhaps prompting this observation. Fortunately overall appearance is sometimes enough, and Rich Hatfield at the Xerces Society identified the bee for us from a photo. Xerces is based in Portland, and is internationally recognized for its efforts at invertebrate conservation. They have produced many useful publications, both in print and online, and issue a quarterly magazine called Wings. Xerces is a very important and well-run organization.

Photos by Anthony Boutard.

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