Stimulating natural supersedure of honeybee queens, Apis mellifera

When a honeybee queen starts to fail, she is often superseded by a young queen that takes over reproduction inside the colony. Natural supersedure in winter leads to an unfertilised young queen and colony loss. To reduce these losses we tried to stimulate supersedure of queens earlier in the season. In 50 colonies we introduced queen cells with one-day-old larvae and capped queen cells. Although many larvae were fed initially, few of them were reared to mature queens and none of the cases resulted in supersedure. This suggests that supersedure cannot be evoked by artificially bypassing the initial phases of the process. When the quality of honeybee queens decreases she has to be superseded. In the process of natural supersedure in honeybee colonies (Apis mellifera) the bees rear a few new queens, one of which replaces the resident queen and takes over the reproduction in the colony (Hooper & Morse 1985). In order to stimulate supersedure of old or failing queens beekeepers use several methods. They may introduce a ripe queen cell (induced supersedure) or a virgin queen in the colony ('Virgin drop'). In this way the old queen remains in the colony while a new queen is introduced. This is in contrast to conventional requeening, in which the resident queen is removed and replaced with a mated queen (Johansson & Johansson 1971). Stimulating supersedure compared to conventional requeening has the benefit that it is cheap, since production of mated queens is not needed. In addition, the bees themselves decide if they accept the young queen or not, which warrants unnecessary replacement of well-functioning queens. Reported replacement rates of induced supersedures using closed queen cells are in the range of 13-17% (Boch & Avitabile 1979, Jay 1981, Szabo 1982). With variable success, replacement rates can be improved by repetitive introductions of queen cells, or by introducing queen cells in tubes that prevent destruction by the bees. Queen cells can also be protected by introduction of the cells in a section isolated from the resident queen using division boards or queen excluders (Skirkevicius 1963, 1965, Forster 1972, Reid 1977, Boch & Avitabile 1979). Honeybee queens normally suppress their replacement by pheromones that inhibit worker bees to construct queen cells (Winston et al. 1989). If natural supersedure occurs, this pheromonal inhibition apparently does not function any more. The old queen lays eggs in a few queen cups, after which the worker bees rear 1 to 3 supersedure queens in 16 days. One new queen remains alive, and after mating she starts laying eggs. The old queen may remain in the colony for some time, but eventually she disappears, either as a result of natural death, or as result of antagonistic behaviour of the new queen or workers (Deyel 1980, Hooper & Morse 1985, Droege 1993). When queen cells are introduced in the brood nest, they are often destroyed by the worker bees (Caron & Greve 1979). This destruction is thought to be induced by pheromones of the resident queen (Reid 1977, Jay 1981). Queens in honeybee colonies used in apiaries maintained for pollination may suffer from transport and unnatural conditions in glasshouses and tunnels (personal observation). Up to 20% of these queens is superseded in the overwintering colonies (personal observation). Since winter conditions limit possibilities for mating flights and drones are hardly available, these supersedures often lead to unfertilised young queens and thus to colony losses. To reduce these losses we tried to stimulate supersedure of queens earlier in the season. A new form of induced supersedure is tested by introducing queen cells with young larvae, instead of introducing capped queen cells. Introduction of queen cells with young larvae bypasses the initial steps of the natural supersedure process. Therefore, bees may be stimulated to supersede queens immediately that would otherwise be superseded during winter.