Current Apicultural Research

From now on each edition of the Newsletter will contain an article about a current topic of bee research. If you are a bee scientist working on a new idea then it may be possible to feature your work here.

To start the series we have an article about the work of a famous bee scientist, Dr. John B. Free, who leads the bee research at Rothamsted Experimental Station in the UK.

A lure that attracts worker honeybees

In a colony of honeybees, members of the colony can communicate with one another by releasing chemical substances which have a particular odour. These substances used for communication are known as pheromones and have been discovered in many species, including man. One of the honeybee pheromones is produced by a gland near the tip of the abdomen of the worker bee, and this is known as Nasonov pheromone, named after its discoverer. The odour of Nasonov pheromone attracts honeybees and in this way individuals are able to locate the rest of their colony.

Dr. Free and his team at Rothamsted haye developed a lure that can attract honeybees. The lure has a similar composition to the Nasonov pheromone which consists of seven terpenoid chemicals: geraniol, nerolic and geranic acidg (E)- and (Z)- citral and (2,B)-farnesol and nerol.

To find the composition of lure most attractive to bees, the researchers Carried out experiments in a bee-proof enclosure made of nylon mesh. Inside the enclosure a machine slowly rotated wire cages containing polyethylene blocks dosed with the chemicals to be tested. Worker bees were put on the floor of the enclosure, and they were watched as they began to cluster on one or more of the cages containing the chemicals being tested. Components of the lure were tested singly and in various combinations, using either very pure chemicals or less pure commercially available preparations. It was found that a mixture of all 7 components of the Nasonov pheromone in equal proportions was at least as attractive as a mixture of the components in natural proportions, and when the mixture was made from commercially available components, it was quite as attractive to the bees as a mixture made from highly purified components.

It has been found that the presence of Nasonov pheromone at the hive entrance stimulates returning foragers to expose their Nasonov glands. Geranic acid, (B)-citral, geraniol and-nerolic acid all increase Nasonov gland exposure, and if they are present in the lure, they increase its effectiveness by stimulating bees to release their own Nasonov pheromone. It was found that the removal of nerol and (E,E)-farnesol from a mixture of impure components made the lure attractive to bees, and these two substances were therefore not included in further experiments in which the lure's effectiveness as a swarm attractant was tested. This time empty hives were placed in the nylon enclosure and a swarm was placed in the centre of the floor. The lures were put in polyethylene vials (whose walls absorb the lure) and hung inside the entrances of some hives. A swarm was placed in the centre of the floor of the enclosure and the bees were then watched to see at which hives they fanned and released Nasonov pheromone, and which hive was finally chosen by the swarm.

From these experiments it was found that in 39 out of 40 tests bees would always choose a hive with a lure. Increasing the number of lures in the hive also made it more attractive to bees. It was found bees preferred previously-used hives containing two empty combs to new or used hives without combs, whether or not lures were present in the hives. Therefore a lure does not mask any attractive effect of combs or odour left in the hive by the previous occupants.

Outside tests using the lure were also done: pairs of Langstroth hives each with two empty combs were placed 2m apart at 50 places in Southern England, with a lure inside the entrance of one hive of each pair. Of the 12 hives which were occupied by swarms, all were those which contained swarm lure.

It therefore seems that the lure developed by Dr. Free and his team does attract swarms to unoccupied hives. It probably works by making the hive easily discovered by scout bees. Use of the lure may make it easier for beekeepers to attract swarms to their hives; this would be particularly valuable in tropical countries where beekeepers depend on migrating colonies to occupy their hives. Other uses for the lure would be to trap honeybees from places where they are not wanted (.g. food processing factories) and perhaps to encourage bees to collect water from a new source or to take artificial food placed inside the hive.

The development of such artificial pheromones" opens up new possibilities in bee management, for example, foreign queens may be more easily accepted by a colony if they are first scented with artificial pheromones.

*To obtain lures please contact Wolfson Unit of Chemical Entomology, Southampton.