Factors encouraging Termite Attack and

General Information about Termites (5)
Factors encouraging Termite Attack and Control of Termites

Factors encouraging Termite Attack

Conditions that put trees under stress are mostly man-made and are the result of poor silvicultural operations. Stress can also be caused by fire, cattle and other pests. In general all actions that decrease the natural resistance of the trees encourage termite attack:

if the soil of the planting site as well as the climate are not suitable, the trees will be weakened and become more susceptible to termite attack in the long run
accumulated waste wood like stumps, tree tops or branches on and in the soil offers additional food for termites
unsuitable nursery techniques result in low quality and thus unhealthy seedlings that are more likely to be attacked by termites
improper planting favours termite attack. For instance a coiled root will strangle itself as it grows thicker and as a result it will start to rot and provide a potential point of entry for termites. Upwards-bending of roots during planting decreases the stability and health of a tree in the long term
damaged bark of the residual trees, caused during tending, thinning and pruning invites termites. The damage can be the result of falling trees, hauled logs or skidders accidentally hitting a tree
compacted soil and mechanically damaged rootlets caused by skidders along log ramps and logging roads affect the health of a tree. If the roots are damaged or not well developed, the tree becomes sick and is then likely to be attacked by termites

thinning operations on steep slopes cause surface erosion that eventually exposes the rootlets of a tree and thus affects its health
cattle grazing and walking in the plantation might cause root damage and stress the tree
the infestation of a tree by other pests can attract termites to the already diseased tree
any stress caused by draught, forest fire, poorly drained soil, etc. encourages termite attack

Control of Termites

There are several approaches to control termites, however none of the efforts is efficient and suitable enough to eradicate established termite colonies in a plantation. Certain problems related to the development of chemical and biological control strategies exist and have yet to be solved. Termites live well hidden in the wood of a tree or in the soil and their galleries are perfectly sealed off. Therefore it is difficult for an insecticide or a biocontrol agent to reach the termites in their colony. Attempts to introduce pathogens or to apply insecticides usually fail, because the termites block off the contaminated area of their nest. The only effective remedy to the termite problem is to prevent termite attack. Since weakened trees more likely to become the target of a termite attack than healthy ones, the main goal of silviculture should be to maintain the trees in a healthy condition. Any operations in the plantation have to be carried out thoroughly and in such a way that stress and the damage to residual trees are minimised as much as possible. Preventive measures are a long-term exercise to avoid termite attack but are not a suitable cure for any existing termite problems. Control strategies are:

Biological control methods seem to be promising, but hardly any organisms are available as suitable and effective control agents. Natural enemies of termites play only a minor role in termite control due to the high number of individuals in a termite colony. Predators of termites are mammals like echidnas or spiny ant eaters, birds such as king fishers and rainbow lorikeets, reptiles like geckos, and lizards, mites, spiders and insects like assassin bugs, ants and some others. However, termites possess a variety of very efficient defence mechanisms that are difficult for a predator to overcome. Ants are potential predacious biocontrol agents but parasites or pathogens are definitely in the better position to tackle the gigantic number of individuals in a termite colony. There are a number of parasites and pathogens of termites, but even these do not really contribute much towards the natural control of termites. Scientists from the Entomology Division of CSIRO are testing the entomopathogenic fungus Metarhizium for the control of termites.
Chemical control is also not suitable in most cases since the target is hidden in the tree and difficult for the insecticide to reach. Previously, insecticides like Dieldrin and benzene hexachloride (BHC) were used for the control of termites but with little success. Now, most of these chlorinated hydrocarbons are banned by the international community and are not supposed to be applied any longer. One exception is the treatment of soil with this persistent class of insecticides in order to control soil-borne termite pests, eg. to protect airstrips. Other control programmes used poisonous dusts of arsenic trioxide and arsenic pentoxide for the treatment of termite nests, but also with little success. Apart from the fact that the termites blocked off the poisoned parts of their nest, these chemicals also had a severely detrimental and often fatal impact on the tree housing the treated colony.
Manual measures comprise digging out subterranean nests or removing arboreal nests and destroying the termite queen. This is however only effective if the whole nest plus all the individuals are destroyed. In some species particular surviving neotenics or pseudergate soldiers can develop into queens and re-establish the colony.

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