Contents - LAC Biosafety

352 Insect pests in plantations: case studies
The geographical distribution of S. malabaricus is limited to peninsular India,
with other species occurring elsewhere.
Impact In teak saplings, the damage caused by S. malabaricus is limited
to tunnelling of the pith and feeding on the bark over a small patch or in
an incomplete ring around the tunnel mouth. In most cases, this damage is
negligible. Rarely, some saplings break off at the point of injury and some
become ring-barked, resulting in death of the top portion. Among plantation
tree species, Acacia auriculiformis, Neolamarckia cadamba, Calliandra callothyrsus,
Casuarina equisetifolia, Eucalyptus spp., Gmelina arborea, Falcataria moluccana and
Sterculia companulata are attacked (Nair, 1987b). A survey in Kerala, India, showed
that the incidence of infestation ranged from zero to 61% in teak plantations
and zero to 11% in eucalypt plantations. In most plantations, infestations
became visible when weed growth was cleared and general observations suggest
that plantations with dense weed cover are more prone to attack. S. malabaricus
attack is not a serious problem except in highly valuable plantations, although
the large larva and the conspicuous frass mat covering the tunnel mouth create
a scare among growers who may fear further spread of attack, without knowing
that the life cycle is annual. S. malabaricus accounted for about 22% of all
requests for advice on control received by the Kerala Forest Research Institute in
India from the State Forest Department, indicating that the perceived impact
was much greater than the real impact (Nair et al., 1996c).
Natural enemies Rare instances of predation by woodpeckers, which
extract the larvae by making a peck hole at the base of the stem, where the larva
rests during the day, were noticed but the larvae are not reachable when in the
root portion. Although many species of ants attack the larvae when in the open,
the frass mat cover affords protection against them. Rare instances of infestation
by the fungus Metarhizium anisopliae, which causes mummification of the larvae,
have been recorded (Nair, 1987b).
Control In view of the low economic importance of S. malabaricus
infestation, no control operation is necessary in most large-scale plantations.
Control is necessary only in high value plantations.
Generally, it is difficult to control borers because insecticides cannot
reach their concealed habitat easily. Methods recommended in the past against
this borer included; (1) allowing naturally growing saplings of more attractive
host plants to remain in the plantation to act as trap plants, and destroying
them later, (2) physical killing by inserting a wire probe through the tunnel
mouth, (3) plugging the borer hole with coal tar or (4) injecting an insecticide
into the tunnel. The first depends on the occurrence of more favoured hosts