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View the documentIn brief

Doorway doses help defeat honey bee's ''vampire'' enemy

They aren't exactly garlic cloves, but strips of plastic impregnated with a pesticide and hung by the entrances to beehives are doing the same kind of service as the legendary anti-Dracula charm in keeping "vampires" away from honey bees.

The vampires in question are actually Varroa mites (Varroa jacobsoni), which feed like vampires, sucking the haemolymph fluid from their honey bee hosts, weakening them and decreasing their resistance to such other bee diseases as foul brood, virosis and mycosis.

A newly developed method al lows beekeepers to ward the mites off, by hanging two plastic strips impregnated with fluvalinate in each hive, one on either side of the entrance, between combs three and four and seven and eight (see photo). As the bees go in and out, they automatically brush their bodies and wings against the strips, picking up small amounts of the pesticide's active ingredient, which is harmless to the bees and leaves no residue in honey, but is fatal to the parasitic mites.

The industrial process by which the plastic strips are impregnated prolongs the effect of the pesticide by slowly releasing it over a period of several weeks after the strips are hung. It takes four to six weeks to eliminate a Varroa population living on worker bees and infesting the brood. This period coincides with four reproduction cycles of the Varroa mite, each cycle lasting 11 days (compared to 21 days for the bees). One treatment per year is usually sufficient, but serious re-infestations may call for additional applications. The most favorable periods for eliminating mites are late summer after harvesting and spring, before the first honey flows. To prevent mites from building up resistance to the pesticide, treatment should not go beyond the recommended periods.

A formidable toe

Even with this new weapon in their arsenal, beekeepers still face a formidable foe in Varroa jacobsoni. The mite, which can be seen with the naked eye, reproduces very rapidly in the sealed brood cell of a hive. Worker bees and drones carry mites while drifting or robbing other colonies, thus spreading infestations rapidly from one hive to another. In extreme cases, infestations have led to the extinction of several bee colonies in a region.

Adult female Varroa mites are red-brown and round-shaped, measuring roughly 1.1 by 1.5 mm. Male mites, smaller and whitish in color, die after mating in the capped brood cells. But the females, hatching at the same time as the young bees, leave the cells with their hosts, to which they attach themselves with their spider-like four pairs of legs. They cling to the hairs between the bees' two abdominal segments, between the head and thorax, or even to the thorax or abdomen, where they feed.

The Varroa mite was first observed in 1904 by A.C. Oudemans, who discovered them on the Asian hive bee, Apis cerana. The Asian bee has long been the natural host of Varroa, with which it has developed a symbiotic host-predator relationship, favoring the survival of both species. Human introduction of the European bee, Apis mellifera, into regions where Apis cerana ranged led to the proliferation of the mite worldwide. Today, Varroa mites have been reported in 58 countries, including the Americas, Europe, North Africa and both the Middle and Far East.

Around 100 species of parasites attack beehives, most of them feeding on pollen supplies or hive debris. But three species of mites - Varroa jacobsoni, Acarapis woodi and Tropilaelaps clareae - feed on the bees themselves. V. jacobsoni, most common of the three, should not be confused with Braula coeca, the common bee louse, which has only six legs and is harmless to bees.

In order to be fully effective against Varroa, the new hive-door treatment must destroy not only the mites attached to adult bees passing through the entrance, but also the young mites that hatch from eggs laid in the bees' brood cells. Since hatching is staggered, infestation occurs daily and consecutively. The strip method, with its prolonged action, is thus a particularly appropriate defence.

Originally developed by Zoecon Corporation (Sandoz group) the strips are marketed under the brand name Apistan. Bayer has also produced a similar product, sold under the name By-Varol. National beekeeping associations or veterinary services can provide information on how to obtain such products. For a modern hive, such as the Dadant 10-comb hive, the treatment (two strips) varies in cost from US$2.50 to $4, sometimes less in countries where Varroa control is subsidized. Experts estimate the cost of treatment at roughly 10 per cent of the value of the honey produced by a hive.

Biological methods are also effective in controlling Varroa mites. One method exploits the mites' need for the sealed brood cells as reproduction sites. Queen excluders are used to make the queen limit her egg laying to one comb, to which the fertilized Varroa females all rush to lay their eggs. If the queen excluder is moved periodically from one comb to another, the total number of mites within a given colony can be significantly reduced.

Major dividends

Effective bee parasite control can bring major dividends, not only to beekeepers, but to agriculture as a whole. As beekeeping development expert Paolo Sartorelli notes: "The direct contribution of pollination to the increase in farm harvests in 20 Mediterranean countries, including Saudi Arabia, reaches US$5.2 billion a year: $3.2 billion for developing countries in the region and $2 billion for the others".

The FAO recently launched a joint program with the European Economic Community (EEC) to combat varroasis and related diseases in honey bees in the Mediterranean basin. The program, to be launched this year, will cost US$50 million, of which US$30 million will be used during the initial, three-year phase. It includes three subregional coordination projects, a regional information and documentation network and a regional coordination project. Training in parasite control will be given at all levels in the countries concerned.

The annual income of beekeepers in the 20 Mediterranean countries amounts to more than US$435 million per year.

Jean-Paul Cadoret