6. Those busy bees -Brian Gant looks at bee behaviour

[This is the first extract of an article originally published in Devon BKA's 'Beekeeping', July 2004. The second part, with reading references, will appear next month. Reproduced here courtesy of BEES]

But how busy are they, and what are they actually doing? One of the earliest observations came in 1855 when Donhoff requeened a colony of black bees with a yellow queen and observed her offspring. He saw yellow bees flying on their eleventh day of adult life but not foraging until the fifteenth. However, when ten days old they were seen in the brood area and building comb.

Later researchers used observation hives, with marked bees and much patience. Thus in 1925 Rosch worked with a 6-frame observation hive in which individual workers were marked as they emerged. Briefly summarised he concluded that the newly emerged workers cleaned cells in the brood nest and then at about three days moved on to feeding older larvae. When about a week old they fed young larvae and soon after started receiving nectar from foragers. At about this time they took their first flight, and a few days later some of them started foraging.

Rosch proposed that all workers went through this sequence with variation in the length of time spent on each task to suit the needs of the colony. These results, and other similar ones, were a valuable first shot at understanding the busyness of the bees. But it is not clear how much the results are affected by the use of a small colony, where the behaviour may not be typical, as well as by the difficulty of recording the activities of individual bees for prolonged periods.

About 50 years ago Lindauer started work by observing the activities of one marked bee for long periods over 24 days, and of another marked bee that was watched continuously, day and night, for her eight days of adult life. The result of these observations was to suggest that there is no clear sequence of hive duties, although one could consider three phases: a short period of cleaning duties, mostly in the first week; then a variety of work in the hive; followed by the final phase as a forager. But with much variation; one marked bee was seen back on cell cleaning work at the age of 22 days; the full range of activities spread across almost the whole of this worker's life, except for foraging.

An interesting feature of these observations is that the individual worker's main activity was 'resting'. On one day this took up 70% of her time and averaged about one-third of the time for which she was being watched. Another third of the time was spent in 'patrolling', walking around the hive but not obviously doing anything. We should remember that for some of this 'resting' time the bee's hypopharyngeal glands may have been producing brood food, or the wax glands making scales, so 'resting' may not be a fair description.

The ability of an individual bee to perform particular tasks depends on the development of the relevant glands. The hypopharyngeal glands will produce brood food for feeding larvae or the queen, or they will produce the enzymes used for processing nectar into honey; but clearly not both at the same time. However, there is no simple fixed sequence of glandular development.

Experiments with very unbalanced colonies - many young bees or many old ones -show that the glands can be adjusted to produce what is required; older workers can reactivate their hypopharyngeal glands to produce brood food if that is necessary, though the transition takes a few days. These glandular changes are associated with the level of juvenile hormone circulating in the bee; this in turn must be influenced by the bee environment.

So Lindauer suggested that the reason for the patrolling activity was to influence the bee according to the current needs of the colony. The exception to all this is foraging, which is limited to the older bees, who do not get significantly involved in tasks within the hive. Foraging is the most dangerous activity and so is limited to the bees who are near the end of their lives and will not perform any of the essential in-hive duties. Ribbands considers that exchange of food by bees within the hive (trophallaxis), also has a part to play in making workers aware of the current needs.

More recent work has been reported by Seeley, who considers that in a normal, balanced colony there is a steady progression of glandular changes apparently linked to a steady increase in the level of juvenile hormone in the blood and a corresponding development in the work done.