Sunday, May 11, 2003		Nature

Honeybees come to know of queen’s death through smell
Nutan Shukla

SMELL and taste are very important for social insects as methods of communication. It is through smell all the many thousands of bees in a hive know whether their queen is alive or not. The message is spread with the help of a particular pheromone named oxodecenoic acid (also known as 9-ketodecanoic acid) secreted from the mandibular glands of the queen. During her nuptial flight she uses the same chemical odour to attract males. Being transmitted from one individual to another this substance reaches all the members of the hive and inhibits the development of ovaries in workers, as a consequence preventing them from taking action to raise another queen. Should the queen disappear or die the workers lacking the queen-pheromone automatically start building, usually on the edges of the comb, conical queen-cells that are larger than the normal hexagonal cells, which constitute the major portion of the honey comb.

Simultaneously, the ovaries of some of the workers begin to ripen and in time they lay eggs in the specially constructed cells. After hatching, the larvae developing in these cells are fed ten times more often than the others by young worker-bee’s protein-rich secretions mixed with pollen and honey, also known as ‘royal jelly’, rather than purely on pollen and honey, effecting development of large ovaries in them. This food seems to have some special qualities because the young larva develops into a queen rather than another worker.

Not only in the case of queens, it has been observed that the career and prospects of all the honeybees are determined by the food they eat. Larvae that are destined to be worker bees or drones are fed on ‘bee bread’, a mixture mainly of honey and pollen. Ordinary workers that are given this diet develop pollen baskets on their legs and stings on their back (a modified ovipository), necessary tools for the kind of life they are destined to lead – protecting the hive and providing food for the hivemates.

It has been observed that whenever bees attack any person their attentions are often directed to one specific spot on the body. Reason for this behaviour is whenever a bee stings it leaves behind minute traces of a pheromone (identified as isoamyl acetate) on the spot. This substance attracts other bees that too direct their attacks to the same particular spot.

Besides above examples these insects also use pheromones to identify their hivemates. Bees’ territory is limited to their hive, which they guard very zealously. Each hive has several ‘guards on duty’ to prevent any intruder, including bees from other hives, from entering. Members of each hive have a distinctive smell, which is in fact an identification mark and nobody is allowed to enter inside without it, and should an intruder approach without this pheromone or an alien smell he is immediately set upon and if possible put summarily to death.

Bees of all sorts collect nectar, but some change it into honey and store in the nest for feeding the young. The main change that takes place when nectar becomes honey is the mixing of nectar with the stomach juices of workers that collect it, along with the evaporation of water content and consequential increase in sugar concentration.

Many insects communicate through the sound produced by their wing-beats, but this is not true with bees. The humming sound produced, due to the vibrations caused by the beating of wings at a very high rate, is just an incidental sound and has nothing to do with their "language", but it does tells the experienced bee-keepers the state of their bees, whether they are excited or their humming is just a normal sound or the hive is without a queen. Usually the frequency of wing-beats in these insects varies between 210 to 290 beats/second, but the average is 225 beats/sec, an equivalent to ‘la’ on the tonic scale and an octave above the sound produced by a tuning fork.

Contrary to bees the acoustic vibrations or the sound produced by wings plays major biological role in establishing contacts between the sexes in mosquitoes. For this both produce sounds of different frequencies so that they can distinguish from a distance whether the sound coming from any individual is male or female. Males usually produce a high-pitched noise with 435 to 480 beats/sec, but in the case of mosquitoes belonging to the genus Forcipomya the frequency of vibrations can reach an astonishing figure of 1000 beats/sec. On the other hand females usually emit a somewhat deeper sound with a slower wing-beats at a rate of about 270 to 350/sec.