The processing factories, and glasshouses where pollination of ﬂowering crops must be carefully controlled or prevented (Free et al., 1984c). In these circumstances lures incorporating the queen pheromone component 9-ODA are especially effective, probably because many of the trapped bees have been isolated from their colonies for some hours. Bees often become disorientated, lost and die when their hives are transferred to glasshouses to pollinate the crops growing in them. Placing Nasonov lures at the hive entrances should help them return home.
Swarms typically choose their own queen rather than a foreign queen (page 105) but this discrimination is largely lost in the presence of a foreign odour, and is reversed when the foreign queen is scented with an artiﬁcial blend of Nasonov components (Boch and Morse, 1981). Therefore the Nasonov lure could be useful when introducing adult or immature queens to colonies, particularly in difﬁcult circumstances. It might also reduce hostility when a beekeeper needs to unite two colonies.
The presence of lures had been shown (Free ez al., 1983a) to increase the consumption of artiﬁcial food (soya bean ﬂour and brewers yeast mixture, pollen, skimmed milk, sugar syrup) placed immediately on top of the brood combs of a colony. They could therefore aid colony development and so improve honey production and pollination in the spring and early summer. The lures also attract bees to consume water. They could therefore be used to condition bees to collect water provided by the beekeeper near to hives, so that they would be less likely to visit water sources (e.g. taps, swimming pools or ornamental ponds) where their presence is undesirable. Attracting bees to water provided inside the hive could be especially valuable in cold weather and early in the year, when foraging can be hazardous.
Lures could be usefully developed to attract the Asian species of honeybees and especially A. dorsata but this must await the chemical identiﬁcation of their Nasonov pheromones.
Attracting foragers to crops needing pollination
If Nasonov gland odour were applied to ﬂowers it would probably attract ‘scout’ bees, in addition to the recruits directed to the ﬂowers by the dances of successful foragers (Free, 1968a). Hence it has been suggested (Boch and Shearer, 1965a; Free, 1970a, 1978) that if Nasonov pheromone could be synthesized and applied economically, it might be used to increase the number of bees visiting agricultural crops needing pollination and so increase seed yield, especially of those crops which are marginally attractive, or less attractive than competing crops nearby.
Despite the potential importance of this, few experiments have been made and progress is slight. Butler et al., (1971) sprayed a mixture of one part citral and 25 parts geraniol to plots containing about 400 dandelion (Taraxacum ofﬁcianale) ﬂower heads; visitation by honeybees was increased compared to unsprayed plots in two experiments (by 54% and 89%) but not in a third. Waller (1970) sprayed small plots of alfalfa (Medicago sativa) with geraniol and citral. On seven occasions the components were provided in dilute sugar syrup and on ﬁve occasions they were applied in water. When applied in syrup, plots sprayed with citral or geraniol alone always attracted more bees than when syrup only was applied, and on ﬁve of the seven occasions a combination of geraniol and citral attracted more bees than either component alone. In contrast when applied in water, either component on its own, or both together often failed to attract more bees than water alone. Oddly, citral seemed to exert the greater attraction in the absence of syrup, and geraniol did so in the presence of syrup. Perhaps syrup had a differential effect on the volatility of the two components.