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Posts tagged “Apidae

Pollen Baskets

Due to their tolerance of cold temperatures, bumblebees can still be found foraging on late-blooming flowers such as New England Asters (Symphyotrichum novae-angliae). Most worker bees collect and carry pollen in a dense mass of elongated and often branched hairs (setae) on their hind legs called a scopa.  Honeybees and bumblebees, however, have pollen baskets, or corbiculae, in which they place and carry pollen back to their hive. Pollen baskets consist of a polished cavity located on the tibia of each of their hind legs which is surrounded by a fringe of hairs. Pollen is pressed on to the pollen basket when it has been collected by the combs and brushes on the inside of the bee’s legs. The bumblebee moistens the pollen with some nectar to make it sticky and stay in the basket. The pollen is loaded at the bottom of the pollen basket, so the pollen that has been pushed towards the top is from flowers the bumblebee visited earliest on her foraging trip. When a pollen basket is full it can weigh as much as 0.01 gram and contain as much as 1,000,000 pollen grains.

Only queen bumblebees overwinter, and they must start a new colony in the spring.  When the queen first emerges you can tell whether or not she has started a nest by looking at her pollen baskets. If she is carrying pollen then she has found a nest site.

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Bumblebees Mating

The adult male bumblebee has only one function in life and that is to mate.  However, research shows that only one out of seven males are successful in this endeavor.  When mating does take place, it is more complex than one might imagine.

In most species, the male bumblebees fly in a circuit depositing a queen-attracting scent (pheromone) from a gland in their head onto vegetation and prominent structures such as trees and rocks.  This usually takes place in the morning, and if it rains, the scent is replaced.  The males then patrol the area, with each species of bee flying at a specific height. Once a (virgin) queen has been attracted, mating takes place on the ground or vegetation, and lasts anywhere from 10 to 80 minutes.  After the male’s sperm has been deposited he inserts a genital plug in the queen which, when hardened, prevents the sperm of other males from entering her for up to three days.  (Photo by Heather Thompson: queen bumblebee with several smaller male suitors)

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Flight of the Bumblebee

bumblebee and turtlehead 049A4838If you examine plants that are still flowering this late in the season (such as asters, goldenrod and late-blooming turtlehead) early in the morning when it’s still quite cool or late in the day, many of the pollinators you see will be bumblebees, not honey bees. One reason for this is that they have different temperature tolerances for flight. You rarely see a honey bee when the temperature is below 57°F as they cannot fly when it is this cool. Bumblebees, however, are capable of flight when the air temperature is as low as 50°F.

Even so, bumblebees cannot take off unless their flight muscles are above 86°F; they maintain the temperature of their thorax (where wings and wing muscles are located) between 86°F and 104°F regardless of the ambient temperature. The way in which they raise the temperature of their thorax involves uncoupling their wing muscles so that the wings themselves do not move. They then use their wing muscles to shiver and raise the temperature of their thorax until it’s sufficiently warm enough for them to fly.

At rest a bumblebee’s body temperature will fall to that of its surroundings. If it is cool out, and the bumblebee wants to take flight, you can actually see its abdomen pumping to ventilate the flight muscles. An entomologist studying this phenomenon discovered that the rate of pumping can give an indication of the temperature of the bee. It ranges from around 1 pump per second when the bee is 86°F, to 6 pumps per second when it reaches 95°F.

New England Aster Providing Bees with Late Season Nectar & Pollen

10-13-14 new england aster & bumblebee 356At a time of year when nectar and pollen sources are few and far between, New England Aster provides many species of bees with food. This composite seems designed specifically for easy pollination. Its open, wide flower shape provides a flat surface for insects to land on, and because the nectar and pollen are not hidden deep inside the flowers, both long- and short-tongue bee species can easily access them. Unlike honeybees, bumblebees do not have a large store of honey in their nests, so they need pollen and nectar throughout the season. Thus, the few flowers such as New England Aster that blossom as late as October are visited frequently and in large numbers. (Only the queen bumblebee overwinters, but the workers continue collecting nectar and pollen up until they die in late fall.)

New England Aster flowers close at night, when there are fewer pollinating insects flying. If an unusually cool period arrives during the time when New England Aster is blooming, the blossoms also close. Although it may seem that the aster is losing pollination opportunities during a cold day, bees are not very active in cool weather.

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