By Geoff Tribe (Images by Jenny Cullinan and Karin Sternberg)
There are many other species of indigenous bees in southern Africa besides the ubiquitous honeybee Apis mellifera which is today essential for the pollination of many introduced food crops. The large carpenter bee (Xylocopidae) which fills the same niche in southern Africa as the bumble bee does in Europe is fairly obvious as it flies about trees in flower such as the keurboom (Virgilia oroboides). Yet there are many other species of much smaller solitary or sub-social bees that play an important role in the pollination of indigenous vegetation. One such interesting group of bees belong to the Allodape and closely related genera which are generally referred to as ‘allodapine bees’ to distinguish them from members of the genus Ceratina or lesser carpenter bees. Allodapines are found in Asia and Australia but are most abundant and diversified in Africa south of the Sahara. What distinguishes them from other such bees is that they have no partitioning cells in their nests and brood is reared in a single burrow and the larvae are fed progressively with small amounts of nectar and pollen made into a paste.
Allodapine bees are usually brown or black with the largest species about 15mm long, but they all have yellowish facial markings either as thin lines or a patch in the lower centre of the face.
They construct their nests in hollow or pithy dead stems, especially where the stems have been broken or burnt to expose the pith. The abundance of nesting sites has a great influence on populations of allodapines and large numbers are able to build up in areas where there are regular nesting sites. Large numbers of allodapine bee nests could, for example, be found in dead khakiebos (Amsinckia calycina) stems alongside railway tracks in KwaZulu-Natal in the 1970’s. Khakiebos was accidentally introduced into South Africa from Chile in fodder purchased for horse feed during the Anglo-Boer War and the weed followed wherever the British mounted troops went. The practice was to spray herbicide on either side of the railway lines to prevent the encroachment of weeds onto the tracks, and this often caught fire and so formed an ideal nesting site for these bees. A small trial showed that a major limiting factor was the number of broken khakiebos stems available for nesting. The number of nests could be greatly increased with the artificial cutting of unbroken stems, so creating access to the pith. Dry flower stalks of Aloe, Watsonia, Gladiolus, Aristea or even the exposed ends of grass thatch of roofs are also used for nesting. This can be observed in the thatch roofs of many chalets in game reserves in South Africa.
Within the allodapines there is much variation in behaviour between species with an intergradation from purely sub-social forms, to semi-social, or primitively eusocial colonies. Sub-social associations consist of one female and her progeny. Eusocial is where there is a reproductive division of labour where the worker caste cares for the young of the reproductive caste and there is also an overlap in generations so that offspring assist parents.
A typical case study of allodapine ecology is that of the eusocial Allodape angulate by S.H. Skaife in the Cape Peninsula. In the winter rainfall region of South Africa adults of the new generation emerge in the middle of summer (end December to February) but remain largely quiescent through the remainder of summer and then disperse in autumn to found new nests. Breeding takes place in July and August and the solitary females begin new colonies. After removing the pith of a broken stem and constructing a burrow, the adult allodapine female usually modifies the entrance to the stem by restricting it by building a collar of chewed pith to fit her size. This nest is then defended either with her head or with her tail end which contains a powerful sting.
The nests of allodapines do not have partitions like those of many other genera in the Xylocopidae, but larvae of different stages of development are reared together in the same tunnel. Several eggs are laid at the bottom of the tunnel which may be as deep as 14 mm and on hatching the female collects nectar and pollen which she forms into a paste. This she places near the head of the larva, and as it develops it is fed progressively. As more eggs are laid, the larvae are re-arranged in the tunnel with the oldest nearest the entrance. Excrement is systematically removed and the tunnel may become stained with pollen. Pupation takes place in November – there being no pupal cocoon, with the pupa merely lying loose near the entrance. Development from hatching egg to adult takes 14 to 15 weeks. When her progeny, both males and females, become adults, some may leave to form their own nests but a few females remain with the old female while assisting in the rearing of the young. Hence the term ‘sub-social’ for the assembly of the old female with about four female progeny over several months. There are many variations on the above nesting behaviour according to the species involved.
Allodapines can be induced to nest in artificial drinking straws or in a bunch of broken pithy stems of a plant with diameters of less than 10mm tied together in a bundle and attached to a peg in the ground. Such bundles of nests can then be moved to a shady and dry place where they may be monitored. Some bees can be induced to nest in clear straws kept in shade and out of direct sunlight where they may be viewed in situ.
Allodapines are usually observed on flowers consisting of a multitude of small flowers on one head where the pollen is found readily on the surface. Such flowers are less regularly visited by the larger honeybees and carpenter bees and are invariably yellow. An example of such a flower is Cotula coronopifilia or ‘gansgras’ (Asteraceae).
Selected references:
Michener, C.D. 1974. The Social Behaviour of the Bees. The Belknap Press. 404pp.
Skaife, S.H. 1979. African Insect Life. C. Struik Publishers. 279pp.
Wilson, E.O. 1979. The Insect Societies. The Belknap Press. 548pp
