Termites

Damage

Termites primarily feed on wood, but some species collect green grasses and seeds and store these in their granaries inside their nest as food reserves. They are sporadic pests, and locally are important on a wide range of crops.

Some termites eat into the taproots of young plants (e.g. cotton and groundnut) immediately below the soil surface, destroying the central root portions, and fill the resulting cavities with soil. Damaged plants wilt and may die within a few days particularly under drought conditions. Some termites also attack the roots of maize and sorghum, and the damaged plants topple. Termites may also travel up through the roots into the trunk and branches. They eventually disrupt the movement of nutrients and water through the vascular system resulting in death of the plant. 

Soil-covered tunnels built by termites on a mango tree.

© A. M. Varela, icipe

Bark-eating termites attack a wide range of crops and occasionally are locally important pests. They cover the tree trunks or plant stems with tunnels built of soil, plant fragments and saliva and gnaw away the bark underneath these tunnels. Some damage is done underground to the roots and underground stem of the plant. The collected plant material is taken back to the nests for construction of fungal gardens. 

Tunnelling damage may kill seedlings or ring-bark trees when large cavities are eaten out of the trees. However, they do not cause damage when feeding on the dead bark of established trees. Sometimes root damage may be serious. Some termites gain access through the dead ends of pruned branch stumps, from which they may invade the living tissues. 

The sugarcane termite (Pseudacanthotermes militaris) causes poor germination of sugarcane setts, and when it attacks mature cane, the can is encrusted with earthen tunnels and stalks are often felled when nearing maturity. This termite is a major pest of sugarcane in East Africa. Other species of termites can also cause considerable damage to sugarcane; under severe attack no shoots can be formed and large gaps are left in the field. 
 

Harvester termite carrying a piece of plant material to the nest.

© B. Loehr. icipe

Harvester termites cut and gather pieces of grass and wood, leaf and herbaceous twigs and carry them to the mounds. They have small earth mounds (about 10 cm) scattered through areas with short grasses. They are major pests of grasslands, and occasional pests of cotton, wheat and groundnuts.

Several species of dry wood and subterranean termites are storage pests and can become a problem in farmers' granaries or in village stores. Most of the damage occurs in wooden storage structures, but some subterranean termites also feed directly on the stored grain. Direct grain losses due to termite feeding are generally low, but contamination with moulds, as a consequence of their attack, is frequent.
 

Host range

Hosts include: Cotton, maize, wheat, sugarcane, upland rice, potatoes, sweet potatoes, groundnuts, soybean, coffee, cassava, tea, cocoa, rubber, oil palm, coconut, some vegetables, some fruit trees like; mango, papaya, citrus, etc.
 

Symptoms

The first signs of termite attacking roots on seedlings or older plants is wilting. Eventually some plants die or fall over. Pulling out the affected plants and examining the roots and lower stem for live termites and tunnelling will confirm the presence of termites. Plant roots and stems may be completely hollowed out and soil-filled. 

Often plants in the field are covered with soil runways or soil sheeting, under which termites may be found. It is important to examine plants in the early morning or late evening, as termites may have moved deeper into the soil during the day when temperatures are high. 

Termite attack on trees and bushes often begins in an area of dead wood produced by pruning or other damage. Small cracks or tunnels made by other insects such as wood-boring beetles may allow winged termites (reproductive stage) to enter. Termites may also travel up through the roots into the trunk and branches. They eventually disrupt the movement of nutrients and water through the vascular system, resulting in death of the plant. 

Galleries in the wooden parts of the construction reveal the presence of drywood termites in granaries. As termites avoid the surfaces of attacked wood, their presence may only be detected after substantial damage has occurred. Subterranean termites construct visible galleries that are used as runways. 
 

Termite damage on mango tree bark.

© A. M. Varela, icipe

Affected plant stages

Flowering stage, fruiting stage, post-harvest, seedling stage and vegetative growing stage. 

Affected plant parts

Leaves, roots, stems and whole plant. 
 

Biology and Ecology of Termites

Entrance to termites nest.

© A. M. Varela, icipe

Termites are social insects, living in large colonies consisting of many workers, soldiers and reproductive forms. They live sometimes in elaborate nests, some build nests on moist dead tree stumps, while others build subterranean nests, which in many cases have mounds that may reach 2 m in height. They forage away from the nest protected through underground tunnels or under soil-covered tunnels. 

Termites feed on dead plant material, such as wood, leaf litter, roots, dead herbs and grasses, dung, and humus. Some termites are able to digest cellulose (wood) with the assistance of symbiotic (mutually beneficial) bacteria present in the gut of the termites. Other termites use the cellulose to cultivate fungi that are then eaten.
 

A termite mound in a mixed cropped farm in Kenya.

© A. M. Varela icipe

Eggs hatch into tiny larvae, which are incapable of feeding on their own and are raised by specialised workers of the colony. Larvae are capable to develop into any caste (workers, soldiers or reproductive forms), depending on time of year, diet etc.

Workers are whitish, wingless and usually blind. They have pale yellow round heads. They comprise the bulk of the population. Workers feed all the dependent castes. They also dig tunnels, locate food and water and build and repair the nest. 

The soldiers are whitish, wingless and blind; they are larger than the workers and have large, brownish heads and strong jaws. With their specialised defensive weaponry, the role of the soldiers is to protect the colony against numerous predators such as ants and centipedes. 

The reproductive termites are winged and are known as alates. Numerous winged males and females, generally dark in colour and with well-developed eyes, are produced for swarming. Swarming is often at dusk after the onset of heavy rains. After flying, they shed off their wings, mate, and burrow into holes in the soil and cracks in wood to found a new colony. The queen termite typically develops an enormously distended abdomen. At her peak, a queen will be laying an egg every 3 seconds or 30 000 a day in some species; and she will lay tens of millions of eggs during her life.
 

Cultural practices

• Promote conditions for healthy plant growth to prevent termite damage. Termites more often attack sickly or water stressed plants than healthy plants.
• Avoid unnecessary injury to the plants as this may facilitate entry of termites.
• Plough field to destroy termites' nest, runways, and tunnels and to expose them to predators, such as ants, birds, chicken, etc.
• Practise crop rotation to reduce the build-up of termites. Planting the same crop every cropping season makes it susceptible to termite attack.
• Grow crops in mixed cropping systems to lessen termite damage. Know and make a list of the annual crops that are attacked by termites.
• Remove plant residues and other debris especially moist and decaying woods. However, take into account that termites may attack plants if there is no other food available, for instance if there are no other sources of organic matter such as soil humus and mulch; therefore ensure there is plenty of soil humus; avoid bare, dry disturbed, organic-deficient, residue-free soil.
• Inspect plants, especially the pruned fruit trees, for termite attack. Do this either early in the morning or late in the afternoon.
• Remove affected plants or part plants, and kill the termites; they are normally found inside the hollowed parts.
• Harvest at the right time, as termites often attack maize, sorghum and millet left in the field after maturity. The attacked stalks may fall down and the termites may attack the cobs and panicles.
• Where there is risk of termite infestation, avoid leaving the crop in the field after harvest on, stacks or windrows.

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