By Karin Sternberg, Jenny Cullinan and Geoff Tribe
Like all living creatures, the honeybee faces many dangers in trying to survive – from environmental hazards such as fires and drought, to the many organisms which wish to feed off their honey and nutritious brood. Those colonies which survive and prosper will be the ones which send out many drones and reproductive swarms which will disperse their genes to the advantage of the species. Because at least 80% of honeybee colonies in Africa are wild (Fig. 1) and relatively few have been hived, the evolutionary pressures acting on the species is being maintained. Even those hived are never domesticated – they have a strong tendency to abscond, for reasons such as starvation or an excess of parasites, or to migrate to seasonal honey flows in adjacent regions. These swarms will in turn be hived again because beekeeping in southern Africa is based on the annual trapping of wild swarms, whether migrating or reproductive, for ‘making increase’ – bringing the number of hives up to optimum again.
Another of the dangers not often pondered are the ambush predators, the robber flies and wasps, many of them generalist predators of soft-bodied insects such as flies, but the diet of several species consists largely of honeybees. The banded bee pirate Palarus latifrons (Fig.2) can be a major problem for beekeepers in the dry, hot and sandy regions of southern Africa. Foraging bees are captured as they leave the hive and are paralyzed by the female wasp which makes a cavity in the soil in which the bee is placed. On this bee the wasp lays an egg which hatches into a larva and consumes the bee.
As many as 80 bee pirates have been seen in front of a hive at the Heuningberg near the town of Porterville on the West Coast. The bees become so intimidated that they cease foraging – only pouring out as the sun sets and the wasps have departed as it cools and they become inactive. The bees fill the entrance with their bodies and create a ‘moaning’ sound which is quite distinctive. The wasps alight on the entrance board and try to entice a bee away from the massively defended entrance. Often the only solution is for the bees to abscond because they are starving.
Robber flies (Fig.3) regularly capture honeybees in flight usually away from the nest where they sit on the sand or perch on rocks or twigs from which they make forays at foraging bees or any passing soft-bodied insect. Around Vachellia (Acacia) karroo trees in flower in the Tanqua Karoo, they tend to perch on nearby rocks and capture the many flies which visit the flowers. There is no information on the numbers of robber flies in any area or any quantifiable data on their detrimental effect on honeybee populations.
The wasps of the genus Philanthus are well known predators of honeybees but will also prey on a wide range of bee and wasp species. The yellow bee pirate Philanthus triangulum which preys regularly on honeybees has another strategy: it ambushes the bees on the flowers on which they are foraging (Fig.4).
It is widely distributed and is common in Europe where it is known as the ‘Bee Wolf’. The wasp stings the bee in the throat which it then malaxates, feeding on the honey which is forced from its crop. The paralysed bee is taken to a burrow excavated in the sand where it is stored in a cell with others to provision the larvae with food in the same way as the banded bee pirate. While observing a bee wolf out foraging on a flower, its behaviour changed when a honeybee came into range. It later dug a nest in a sandy bank and then flew off only to return 12 minutes later with a honeybee it had captured (Fig.5).
Recently vast numbers of wasps of the Bembix genus were observed in the vicinity of honeybees drinking water in seepage beside a stream in the Cape Point section of the Table Mountain National Park. With temperatures as high as 36°C a number of bees were collecting water (Fig. 6).
Tracking Bembix in the late afternoon light, we found an aggregation of about 50 nests located in soft soil on the bank above the stream and many Bembix furiously and almost chaotically digging at the surface at intense speed creating new nesting sites (Fig.7). Bembix wasps do not have it all their own way. Adult wasps are preyed on in turn by some birds, lizards and antlions, Neuroptera and probably also crab spiders, robber flies and mantids; while bombyliid flies are known parasitoids of their larvae, and chrysidids, cuckoo wasps, mutillids (velvet ants) and true ants are known to rob Bembix nests. One of the Bembix observed was carrying a winterschmitiid mite (Fig. 8), attached to the thorax with its suctorial plates. Many of the mites are phoretic, travelling on the body of adult insects without being a parasite. (S. Gess, pers. comm).
The alien European wasp, Vespula germanica (Fig. 9), is now firmly established in the south-western Cape and with time will migrate up the eastern coast into other provinces. It nests in the ground, as opposed to the other invasive wasp, Polistes dominulus, also from Europe which makes grey ‘mache’ nests the size of a football under the eaves of houses. Vespula germanica feeds on soft bodied insects including honeybees at flowers and is able to raid hives, collecting both adults and brood to feed to their larvae. The mild climate in southern Africa allows them to build massive nests in the ground, to persist throughout the year, and to invade the fynbos.
There is a great variety of organisms which feed on honeybees, of which those which have a close association are recorded and their biology mostly unraveled. But there appear to be yet many more opportunistic species of predators of honeybees which are only rarely recorded when they are chanced upon. They occur in diverse environments from fynbos to semi-desert biomes and their slow attrition on the numbers of foragers must ultimately have an effect on the well-being of the honeybee colony.
Pulawski, W.J. and Prentice, M.A. 2008. A revision of the wasp tribe Palarini Schrottky, 1909 (Hymenoptera: Apoidea: Crabronidae). Proceedings of the California Academy of Sciences, Series 4, 59(8): 307-479
We are grateful to Dr Sarah Gess of the Department of Entomology and Arachnology, Albany Museum for the information supplied concerning these wasps.
The authors at work: