Contents - LAC Biosafety

10.7 Eucalyptus species (Myrtaceae) 229
extensive feeding occurs from the root collar downwards. In Africa, even saplings
up to 15 cm diameter at base may be attacked and killed by some species of
Macrotermitinae. Nair and Varma (1985) recorded unequivocal evidence of
vigorously growing saplings suddenly killed by termites. Similar observations
were made by Nkunika (1980) in Zambia. In general, primary attack of healthy
saplings accounts for the greater part of eucalypt sapling mortality caused by
termites.
Secondary termite attack Roots of saplings killed primarily by other causes
and standing in situ are subsequently eaten up by termites. Drought is one of the
primary causes of death, particularly in shallow soil near rocky outcrops; root
infection by pathogenic fungus is another.
Complementary termite attack In this case, termite attack complements the
action of other factors and the combined effect leads to death of the plant. Thus
termite feeding on the roots may complement the action of drought, fungal
infection, root coiling due to faulty bagging, mechanical injury etc. Each factor
by itself may be sublethal or slow acting.
In India, peak incidence of termite attack occurs within about four months
of planting out the container saplings (Fig. 10.11), although staggered deaths
continue to occur almost every month during the first year, sometimes with a
Fig. 10.11 Progress of incidence of termite attack in out-planted eucalypt saplings
in Kerala, India, in various field trials in the years 1976–9. The lines show cumulative
mortality of saplings in the untreated controls and in some ineffective insecticidal
treatments. The bars show mean monthly rainfall for the three years. Date of
planting indicated by arrow on the x-axis. Adapted from Journal of Forest Ecology and
Management (Nair and Varma, 1985), with permission from Elsevier.