Termites

Pests of Field Crops in Southern Africa

TERMITES

(Isoptera: Termitidae)

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Text Box: In the drier regions of southern Africa, termites, often popularly called "white ants", can cause a good deal of damage to a variety of crops. A number of species have been implicated: Macrotermes spp., which may be recognised by their large size, white bodies and golden-red heads, and the large mounds ("ant hills") they build. Odontotermes spp., which are smaller (about 4 mm long), white-bodied, with golden heads, and which build smaller mounds with large open ventilation shafts, particularly in black “vlei” areas. Ancistrotermes latinotus, a small species that looks very similar to the above but which does not form mounds at all, merely living in series of underground hives or occupying portions of hives belonging to other termites. Microtermes spp., which is a minute termite (about 2 mm long), similar in appearance to the above two, and which also does not build mounds. The harvester termite, Hodotermes mossambicus, belongs to a different family and is not included here, as it is a more specific pest of grasses and pastures. Macrotermes sp. are often erroneously called harvester termites, but they differ in appearance (being much paler in body colour than the pigmented harvesters, although of similar size) and in their food-collecting habits (they do not wander freely, but build mud tunnels over their food source). TOP

Text Box: Among the crops which have been subject to termite damage are cotton, deciduous fruit trees, groundnuts, maize, pasture grasses, plantation trees, sorghum, soyabeans, sugar cane, tea, tobacco and wheat. Also attacked are lawns and various ornamentals. Plants are readily attacked when they have been damaged or have been under some form of stress, such as drought or sometimes even water logging. Not surprisingly, timber is sometimes damaged by the species mentioned, as dry wood is their natural food, but other species are usually implicated. TOP

Text Box: Damage takes on various forms, depending on the crop. In cotton, most of the damage takes place in the first nine weeks after planting, and the termites (Ancistrotermes, Odontotermes and Microtermes spp. particularly) tend to penetrate and hollow out the taproot and stem from beneath the soil. Affected plants then simply wilt and become desiccated. In maize, the smaller termite species may hollow out the roots and lower stem, but this seems to occur after physiological maturity of the crop. The result is lodging and then rapid covering of the fallen plants with earth workings so that they can be consumed, cobs and all. Sometimes Macrotermes spp. from a nearby mound may attack the crop, and they approach from above the ground, simply covering the lower stem with earth and climbing up the plant. In groundnuts, damage appears from about twelve weeks after planting, and taproots and subterranean pods may be hollowed out. This allows the penetration of fungi into the pods, one of which in particular, Aspergillus flavus, produces a substance (aflatoxin) which is highly toxic to cattle and poultry. In other plants, damage may be more obvious, with earth-workings around the stem bases. Often, weakened or stressed plants (from drought or a spell of water logging) are attacked. TOP

Text Box: A number of different forms of individuals exist in termite communities. Every colony has a king and queen, whose sole concern is reproduction, and these are often enclosed in an earthen cell where the hugely distended and helpless queen produces thousands of eggs. If destroyed, the royal couple can be replaced by complementary royalties which are reared by the workers. The soldier caste is easily recognised by the enlarged, pigmented head and usually well-developed jaws. “Soldiers” surround the openings of mounds or earth workings and protect the workers while they are on food forays. The greater part of the colony consists of the workers, which are concerned with food gathering, nest building and care of the eggs and young. They also feed all the other members of the colony, which are unable to feed themselves. Many termites of the family Termitidae cultivate a fungus within the nest, and this is a source of food for the royal pair and the young. When the rains arrive, activity in the colony increases, the hives are enlarged, and a winged form appears. These termites are fully developed sexually, and have the task of mating and founding new colonies. Vast flights of them appear when weather conditions are ideal, and after mating, the wings are dropped and each pair finds a new home. They form an important source of food for many other animals, and relatively few succeed to start new colonies. TOP

Macrotermes mound.

Soldier and worker termites.

Termite damage to groundnuts.

Macrotermes soldier.

Harvester termites (below) are pigmented, unlike crop damaging termites above.