By Nokuthula Mbanyana-Nhleko and Simon van Noort
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Africa is home to more than 20 000 described species of ants, bees, wasps and sawflies (Hymenoptera). Awareness of these insects usually centers on the larger species that sting or bite, but by far the majority of species are tiny insects that are highly abundant in most terrestrial landscapes and not noticed because of their small size. Like other insects, they are found in almost all terrestrial habitats, but are not uniformly distributed across regions, with factors such as climate, vegetation and soil affecting their evolutionary diversification and current distributions.
Ants, bees and wasps are often considered as a nuisance by many people, with ants foraging around picnic sites and getting into many food items; and wasps and bees showing up uninvited with nasty stings. But – a world without these insects would be catastrophic for ecosystems and humankind.
They contribute immensely to ecosystem health and to the economy, as they play a critical role in the functioning of all ecosystems, including maintenance and evolution of floral species richness through pollination of flowers; recycling of nutrients by breaking down organic matter; and insect population control via predation and parasitism. Without pollination services provided by bees and wasps, many plant species would go extinct. One in every three mouthfuls of food you eat is dependent on the pollination services provided by bees!
This large order of insects (Hymenoptera) is second only to the beetles (Coleoptera) in terms of described species, and is likely to be even more species rich if the undescribed species are taken into account. Hymenopterans are poorly known from a taxonomic and species richness perspective, with an estimated 20% or less of the extant species known to science. Although around 20 000 species are already known from Africa, the total number of species is estimated to be somewhere between a hundred thousand and half a million, so there’s still much work to be done to document and formally describe the unknown species.
As part of an international team devoted to documenting this unexplored species richness, the two entomologists at the Iziko South Africa Museum – Simon van Noort and Nokuthula Mbanyana-Nhleko – focus their research efforts on unravelling the systematics, evolution and biology of Hymenoptera from Africa; and in the process, they discover, document and describe new species.
As part of the Afrotropical Hymenoptera Initiative (www.waspweb.org), Simon van Noort described 84 new species of African wasps during 2019, 35 of which are from South Africa. These revisions were centered on material collected over the last thirty years by entomologists at the Iziko South African Museum.
With increasing rates of anthropogenically induced habitat destruction, and habitat transformation due to climate change, implementation of ongoing invertebrate inventory surveys of South Africa’s diverse ecosystems is a matter of priority. The resulting samples, safe-guarded in South African museum collections, are necessary to provide essential baseline data for assessing rates of spatial and temporal change in our invertebrate species richness and abundance.
Currently we have very limited baseline data on South Africa’s invertebrate species richness available to assess the local extent of the insect Armageddon the globe is experiencing. There is no doubt that in South Africa we are also rapidly losing much of our biodiversity heritage – yet we have no idea of the rate at which this is happening. With leverage of appropriate resources, our natural history collections and the research conducted by world specialists on South Africa’s rich fauna will provide the data required to make these critical assessments.
Almost all the ants that you see on the ground are females. These are workers and they are responsible for nest construction, foraging and tending to the brood and queen. A typical ant colony contains an egg-laying queen (Fig. 2), adult workers (Fig. 3), brood (eggs, larvae and pupae) Fig. 4 and males (Fig. 5).
Ants provide essential services for maintenance of ecosystems. In arid and semi-arid regions, seed harvester ants gather seeds and store them in their nests to be consumed at a later stage. The seed husks and other plant matter collected and stored by these ants get mixed with the organic matter content present in the soil (Fig. 6). In Fynbos regions, it is believed that seed harvesters contribute significantly in maintaining the structure and diversity of the region, as they play an important role in seed distribution and survival. They either harvest the seed and consume the contents, or gather and disperse the seeds. These seeds become abandoned in their galleries, which benefits the seeds, as they are protected from fire and predation. Most plants, particularly those that have nutritive bodies (elaiosomes) attached to their seeds use ants as their seed dispersal agents (Fig. 7). Ants drag the seeds to their nests to feed on these fat-rich bodies, and then discard the unharmed seeds underground where it is protected until germination.
Most ant species nest in the ground. Nest excavation by ants positively affects soil properties as the process of excavation results in the mixing of subsoils, top soils and organic matter from above the surface – which increases the levels of soil nutrients (Fig. 8). Their nests have tunnels and chambers underground; and these chambers increase soil porosity, which in turn enhances infiltration rates in soil.
Ants are also regarded as good bio-indicators, because they respond very quickly to drastic changes in soil and vegetation structure due to anthropogenic habitat disturbance or pollution. They are effective colonisers of disturbed and open spaces, and therefore surveying ant diversity is a useful tool for assessment of ecosystem recovery after land transformation.
Ants also provide protection to certain plant species. These plants provide nectar to ants through flowers or extra-floral nectaries (Fig. 9), and accommodation in the form of hollow thorns or stems; the ants, in return, protect the plants against herbivores (Fig. 10). Ants may also be used as biological control as most species are predators (Fig. 11).
These insects are considered as major pollinators for both wild and garden plants. Those that belong to the family Apidae have pollen baskets on the outside of the first segment of the rear tarsi (Fig. 12; 13 & 14). Without bees, many flowering plants would be extinct. They also have economic value, as they produce honey, beeswax, royal jelly and propolis – products that are exploited commercially.
Carpenter bees and mites have evolved a special relationship. Three brown phoretic mites are visible protruding from a special cavity, called an acarinarium, on the abdomen of a female Xylocopa caffra, foraging for nectar and pollen (Fig. 15). The cavity has evolved specifically to transport mites. The relationship is an example of a mutualism that is of benefit to both the bee and the mite. The mites hitch a ride from the nest the bee developed in to any new nests that she constructs for her off-spring. The mites feed on fungi in the nest keeping it away from the pollen provisions and her larva. Click HERE
Most species of wasps belong to a group called Apocrita, meaning that they have modified ovipositors for different functions such as laying their eggs on, or into their prey, or into plants to form galls using elongated tubular organs called ovipositors (parasitoid wasps Fig.17); or as a stingthat can be used to inject venom to subdue invertebrate prey, or used as a defense mechanism against vertebrates (predatory and social wasps).
Parasitoid wasps are used as biological control agents as they control population abundance of insects, many of which are pests, by attacking the host insect, often a moth caterpillar or a beetle grub. They are beneficial to society as they play a vital ecological role as natural controllers of insect populations (Fig. 17), including those that are detrimental to agriculture, forestry, human and animal health, and hence have vast potential for use in managed bio-control programs, reducing the need for insecticides.
Many species of braconid and ichneumonid wasps play important roles in controlling caterpillar and beetle grub pests on crops. Many of the much smaller chalcidoid wasps are extensively used for biological control of invasive plant and insect species. They play an integral part in cultivated gardens, and commercial agricultural and forestry enterprises as they protect crops and plantations by controlling and reducing pest insects.
Predatory wasps prey on insects to feed their larvae, and therefore minimize the need to use toxic pesticides in gardens (Fig. 18). Like bees, some species of wasps are considered to be essential pollinators. Many specialized plant-wasp interactions have evolved over millions of years, most notably the obligate mutualism (neither partner can survive and reproduce without the other) that exists between pollinating fig wasps and their host fig trees (Fig. 19). The fig wasps can breed nowhere else except for within figs, and fig trees cannot reproduce without the pollination services of the fig wasps.
Usually pollinators are rewarded by the plant with a source of pollen and /or nectar, which they use themselves or for development of their offspring. Other fascinating interactions include trickery of wasps. Certain species of orchids rely on wasps for pollination; the orchids have flowers that trick male wasps into attempting to mate with them by mimicking female wasps through scent and colour. When the male wasps attempt to copulate with the flower the wasp is covered with pollen, which is then transferred to the next male-seducing orchid. Without these wasps, these orchids would not be able to propagate themselves, and the same holds for a diverse array of our other plant species making up South Africa’s rich floral heritage.
This highly diverse order of insects forms a major part of the Entomology collection housed at the Iziko South Africa Museum (Fig. 20). This is one of the largest and oldest insect collections in Africa, housing over a million dry insect specimens. Specimens date back as far as the 1860’s (Fig 21 & 22) and the collection has been slowly built up ever since then, through active field work conducted by Iziko scientists – mostly of which has been conducted within South Africa, however the results of expeditions to other areas of Africa have also been mounted.
In the field, researchers collect specimens using a diverse array of sampling methods including Malaise traps (Fig.23), yellow pan traps (Fig.24), pitfall traps (Fig.25), sweeping (Fig. 26), active collecting (Fig. 27), rearing, UV light trapping (Fig. 28), canopy mist fogging (Fig. 29), and extraction of leaf litter (Fig. 30 & 31). Rigorous documentation of the associated data is required. Detailed data of each collecting event is recorded, including all information related to the sample/specimen, such as locality (with co-ordinates), date of collection, collector, and method of collection, host plant/animal association, habitat and any other biological associations that are observed.
The sample is subsequently curated and sorted into the different groups of insects, and if possible to morpho-species by research technicians (Fig. 32) using morphological characters. Specimens sorted into families or genera make them available to international research scientists who – through a process of laborious detective work – assess whether the newly collected specimens represent new species or not.
This process entails a thorough assessment of the published scientific literature, examination of the type specimens (Fig. 21) of previously described related species, and assessment of the morphological characters that define species within the genus under study. New species are formally described and photographed using high tech imaging systems (Fig. 33), and diagnoses are provided, explaining how the new species can be distinguished from all related known species. An identification key is also produced to facilitate the identification of any new specimens subsequently collected by various biological agencies. The taxonomic revision is required to be published in a recognized scientific journal according to the rules encapsulated in the International Code of Zoological Nomenclature. The published taxonomic revision provide a resource that can be used to reliably identify the species within the group that was treated. These resources are widely used by various sectors of society, such as conservation agencies to enable informed conservation assessments, the agriculture and forestry industries, and scientists such as ecologists who will use this resource to identify the species involved in ecological interactions they are investigating. An accurate method of species identification is crucial for estimating diversity and for understanding their distribution patterns, critical elements for effective conservation management of our diverse ecosystems.
For further details of research output conducted on the Entomology collections at the Iziko South African Museum, please visit the following web sites: