Termites: the good, the bad and the ugly

Termites of many different kinds are found throughout the tropics. Little is known about their impact on agriculture, even though there have been many studies of the social organization of termites within their colonies. What influence do termites have on soil fertility, for example, and what is the extent of the damage they cause to crops? The answers to these questions are to be found by observing farmers' practices in the field. Harmful or beneficial, the results are many and varied. Dr Yao Tano, a scientist at the Laboratory of Animal Biology at the University of Abidjan, concedes that 'people who study termites are more likely to be interested in their advantages than their disadvantages.' However, despite this natural tendency, he has established subtle differences between the three principal categories of termites, distinguished by their feeding regime and the easily-recognizable shape of their mounds. The fungus termites, of which Macrotermes are the most widespread, are the most damaging. Their 'cathedral' mounds are the highest, reaching 6m or more in height, whereas the mushroom-shaped mounds built by decomposers (Cubitermes) or the dome-shaped mounds of the forager termites (Trinervitermes), are usually less than a metre in height. The fungus termites derive their name from the symbiotic fungal growth which they maintain as a food source on macerated wood within the mound. But these termites also eat maize, groundnuts, yam and other crops. Decomposers eat decaying vegetable matter and therefore have a direct influence on the formation of humus as do the foragers, although to a lesser extent. The latter are more interested in wild grasses and, incidentally, in the leafy matter of cultivated crops. A greater proportion of total crop losses attributable to all types of termites is thought to be the result of attack in the field rather than from damage in grain stores. Actual percentages vary greatly from one region to another and, for the most part, have yet to be established. However, 'it is reasonable to estimate that losses in the field, particularly of maize crops, may exceed 15% in some savanna zones.' For some monocropping systems, such as rice cultivation, the losses are such that small-scale farmers are discouraged from attempting them. And when fungus termites invade a field of groundnuts (one of the crops most vulnerable to termites) the potential yield may be lowered by 20% or more. Even though their damage is significant, it is much less than that caused by some other insects, for example, stem borers.' Farmers, who are not always aware of the difference, often attribute damage to termites which is actually caused by stemborers. Although for the most part losses in production are due to termite attack on the crop itself, the fungus termite creates an added problem with its huge mounds. The base of these may reduce available soil surface by as much as 10% or more and thus restrict land available for cultivation. Recycled termite mounds As for the beneficial effect of termites on soil fertility, in particular the fertility value of some termite mounds, 'little is known other than that which farmers have known for a long time.' says Yao Tano. He is currently conducting trials in the Touba region in the north of Cote d'lvoire to quantify the effect on soil fertility. Solve authors mention that farmers in East Africa, notably Tanzania, use the mushroom mounds of decomposer termites as fertilizer. These small termite mounds can, up to a point, improve soil fertility in, for example, a home garden or, on a small scale, along ridges or mounds. In practice, the presence of such termites indicates to farmers that the soil is good and worth cultivating. The base material from which the huge, cathedral-like termite mounds are constructed is poor in both mineral and organic content They are made from fine particles of clay which the termites bring to the surface from Macrotermes cathedral mounds can reach a height of 6m or more. The termites construct these mounds by baring deep into the earth sometimes to a depth of 20m The light clay that constitutes the visible part of the mounds is very poor in both mineral and organic content and d is therefore of little agricultural value as much as 20 metres below ground. If the mounds are broken up, or eroded, they deposit a large quantity of fine, clay particles on the surrounding soil surface thereby reducing aeration and water infiltration. It is not surprising, therefore, that farmers look upon Macrotermes as a curse and try to get rid of the pest by destroying the queen. In general, if the queen is killed, so too is the rest of the colony. Farmers may also use chemical insecticides, 'but the insecticides are not selective and they kill not only termites but also beneficial worms. An effective means of getting rid of Macrotermes would be very greatly appreciated by farmers' says Yao Tano. Ants could one day provide a solution to the problem of damage caused by Macrotermes. Ants are termites' natural and most formidable enemies and a team of French scientists has identified 'a species of ant which emits a toxic substance capable of killing an entire termite colony.' Even if the colony is destroyed, the problem of the 'cathedral' mound remains. The solution could be to use the clay of which the mounds are constructed to make bricks. This is being practiced on a large scale in the north of Zambia and the south-east of Zaire. It may be recalled that in 1985 a team of scientists from the Department of Geography at the University of Lubumbashi in Zaire and at the Laboratory of Ecology at the Faculty of Agronomic Sciencies at Gemboux, Belgium, initiated the construction of several large cities (Lubumbashi, Likasi, Kolwezi and Ndola, which now have between 125,000 and 700,000 inhabitants) from material taken from the termite mounds in the area. University of Abidjan Laboratory of Animal Biology BP 582 Abidjan 22 COTS D IVOIRETermites of many different kinds are found throughout the tropics. Little is known about their impact on agriculture, even though there have been many studies of the social organization of termites within their colonies. What influence do termites..