J. B. Free

Factors determining the rearing and rejection of drones by the honeybee colony

Abstract Production of drone cells and drone brood and the eviction of adult drones by honeybee colonies have been investigated. Smaller colonies of honeybees either built no drone comb, or a smaller proportion of drone-to-worker comb than larger colonies. The proportion of drone cells built was greatest in May, June and July although colonies continued to build drone comb long after they had ceased to rear drones. The proportion of drone comb built by a colony also depended on the amount of drone comb already present. The amount of drone brood and the number of adult drones present in a colony was correlated positively with the number of workers. Removing drone brood from colonies encouraged its production, adding it diminished its production. A large percentage of eggs was sometimes laid in drone cells before the end of April, although few were reared. The proportion of drone brood was at its maximum in May and June. A colony could be caused to evict its drones by preventing it from foraging and in autumn eviction was greatly delayed by providing forage or removing the queen.

The feeding and mating behaviour of pollen beetles ( Meligethes aeneus Fab.) and seed weevils ( Ceutorhynchus assimilis Payk.) on oil-seed rape ( Brassica napus L.)

During the early period of infestation of winter rape, pollen beetles and seed weevils were mainly feeding and attaining sexual maturity. Before a crop flowered pollen beetles fed on buds but only some of those which they had perforated to obtain pollen dropped off. When flowering started adults obtained pollen from flowers rather than from buds. They laid their eggs in the buds but not in the flowers. Larvae moved from flower to flower up the raceme and caused no damage. Probably many podless stalks have been wrongly attributed to pollen beetle damage. Overwintered seed weevils caused no damage by feeding on rape pods. New generation seed weevils caused some loss of seed weight and viability when feeding on pods of spring rape; this is probably unimportant on a field scale. Pollen beetles and seed weevils mated from mid-May until the emergence of new generation adults; these did not mate before hibernating.

The distribution of insect pests on crops of oil-seed rape (Brassica napus L.) and the damage they cause.

During 3 years the distribution of pests on ten crops of winter rape and two of spring rape, and the damage they caused, has been determined. During immigration the adults of all pests infested crop edges more than crop centres, particularly on large crops, irrespective of the presence of wind breaks. The proportion of M. aeneus and G. assimilis at the crop edge gradually diminished as they moved further into the crop, and their larvae and pods with C. assimilis emergence holes were more evenly distributed over the crops than the adults. Damage by M. aeneus was not the only cause of podless stalks. The larvae of D. brassicae were largely confined to the edges of crops; split pods were largely but not solely confined to the edges. In winter rape crops correlations were found between the percentage of podless stalks per plant and the number of M. aeneus present, and the percentage of pods infested with C. assimilis larvae and the adult C. assimilis population. In two fields infested with D. brassicae the diminution in the proportion of split pods from crop edge to crop centre was positively correlated with diminution in the number of adult D. brassicae .

Pollination as a factor limiting the yield of field beans ( Vicia faba L.)

Self-pollinating and cross-pollinating by hand samples of flowers in field bean crops usually gave an increased set of seed compared with control flowers left to be pollinated naturally. Hence, insect pollination of field bean crops is often inadequate. In large fields of more than 12 ha the seed yield was greater by plants near the edge than near the centre. Fewer pods were produced from nodes at the upper than the lower parts of a stem, and they contained fewer seeds which were of a smaller size.

Hoarding by honeybees (Apis mellifera L.)

Abstract The food hoarding by groups of fifty bees kept in small cages and provided with sugar syrup was studied. Less food was stored in a new comb than in an old one, whether the old comb had been used for storing food or rearing brood, and there was less in drone than in worker combs. The presence of light, larvae and the odour of honey discouraged storage of syrup, but the presence of a queen encouraged it. The amount stored also varied with the environmental temperature, the age of the bees concerned and with their previous physiological and behavioural experience including food deprivation and length of confinement. Increased food in honeystomachs sometimes compensated for less stored in combs.

A survey of the damage caused to crops of oil-seed rape ( Brassica napus L.) by insect pests in south-central England and their effect on seed yield

No correlation was found between the seed yield per plant of oil-seed rape, the percentage of podless stalks and the percentage of pods infested with seed weevil larvae. The weight per seed and the percentage of podless stalks of winter and spring rape plants were similar. In winter crops the mean number of seeds per plant, weight of seeds per plant, and number of pods per plant were greater near the crop centre than near the crop edge. Plants with relatively few seeds tend to compensate by having heavier ones. Pods infested with seed weevil had fewer and lighter seeds than pods not infested, but the overall decrease in weight of seed per pod was small. The proportion of pods infested with seed weevil in winter rape was twice that in spring rape plants, but was not great. In lightly infested fields the weevils were concentrated at the edges, but the opposite occurred as infestation increased. Infestation of pods of winter rape by seed weevil increased with the number of years rape had been grown on the farm. There was no correlation between insecticide application and yield, but the number of insecticide applications to spring rape crops was positively correlated with the number of years for which the farmer had grown rape.

Repelling foraging honeybees with alarm pheromones

The honeybee alarm pheromones 2·heptanone and isopentyl acetate were repellent to honeybee foragers when applied to plots of oil-seed rape and field beans and to sunflower heads. Their possible use to repel bees from crops before insecticide application is discussed.

Managing honeybee colonies to enhance the pollen-gathering stimulus from brood pheromones

Abstract Experiments showed that when the hive entrance of a colony led directly into the brood area, the foragers collected much more pollen, and so were more valuable pollinators than when it led into the storage area only.

The pollination of hybrid kale ( Brassica oleraceae L.)

Honeybees were able to distinguish between the flowers of two different oultivars of kale grown to produce hybrid seed and most foraged only on one or other of them.

Foraging of bees on oil-seed rape ( Brassica napus L.) in relation to the stage of flowering of the crop and pest control

Large populations of bees often continue to forage on oil-seed rape crops until flowering ceases. Applications of insecticide to crops in the late flowering stage could be hazardous to these bees.