Contents - LAC Biosafety

228 Insect pests in plantations: case studies
Fig. 10.10 Characteristic dumb-bell shaped region in the below-ground portion of
a Eucalyptus tereticornis sapling, formed by termite feeding, prior to severance of the
root system. Reprinted from Journal of Forest Ecology and Management (Nair and
Varma, 1985), with permission from Elsevier.
In the out-planted clonal plants which have no taproot, the termites attack
the stem portion of the plant in the soil, causing ring-barking. Termites also
feed on the small adventitious roots (Varma, 2001).
There has been some debate in the literature as to whether termite attack on
eucalypt saplings is primary or secondary. Some authors have claimed that
termites will attack only those plants that are weakened by other causes such as
drought or fungal infection, and others have suggested that increased plant
vigour will lessen the liability of termite attack. The idea that termite attack is
secondary has stemmed from the fact that termites do attack saplings that have
been killed or greatly weakened by other causes and it is often difficult to
distinguish between the primary and secondary causes. Based on detailed field
observations, Nair and Varma (1981, 1985) recognized three kinds of situation.
Primary termite attack This is common in eucalypt plantations up to one
year old in India and many other countries, and also in somewhat older
plantations in Africa. In smaller saplings, the taproot is attacked a few
centimetres below ground surface and tapered off, whereas in older saplings,