Contents - LAC Biosafety

10.17 Tectona grandis (Lamiaceae) 327
a neighbouring tree if it has only mature leaves. Such a tree does not suffer
defoliation, unless older larvae migrate to it from adjacent trees after consuming
the available foliage. Extensive field search did not give any indication of the
existence of H. puera-resistant teak trees. Through field observations on marked,
escaped trees, it was shown (Nair et al., 1997) that a tree which is not attacked
in one year might be attacked in another year. Due to asynchrony between
the flushing time of trees and the time of arrival of the immigrant moth
populations, different trees may escape defoliation at different times. Based
on laboratory screening of excised leaves or observations on susceptibility to leaf
damage in clonal orchards (gene banks), some workers have classified various
clones as highly resistant, resistant, susceptible etc. (Ahmad, 1987; Jain et al.,
1998, 2002), but in the light of the above observations these results should be
interpreted with caution. However, there is at least one variety of teak, known as
‘teli’, in Karnataka, India, which flushes about a month earlier than others and
usually escapes defoliation (Kaushik, 1956). Since H. puera is unlikely to adapt to
an early flushing variety of teak as the moth arrival time is dependent on the
arrival of the monsoon, the scope for using this variety in an IPM programme
needs further study (Nair, 1998).
Pheromonal control The female moth displays the characteristic calling
behaviour prior to mating (Sajeev, 1999) and the male moth possesses the
characteristic hair brushes on the hind legs (Sudheendrakumar, 2003), suggesting
the presence of a mating pheromone, although this has not been isolated.
There is little scope for use of the pheromone for controlling the outbreak
populations of H. puera, because of the mass influx of the moths. However
pheromone may be of use as a population monitoring tool.
Biological control using microbes Commercial formulations of B. thuringiensis
(Bt) have been found effective in laboratory as well as field trials (Singh and
Misra, 1978; Kalia and Lall, 2000; Loganathan and David, 2000; Senguttuvan et al.,
2000). Senguttuvan et al. (2000) recorded 100% knock-down toxicity of Bt to third
and fourth instar larvae within eight hours of their feeding on leaf disc treated
with water containing 159 IU/ml of a commercial preparation of Bt. In field
trials, 90–99% mortality of larvae were obtained with commercial preparations
of Bt at 0.2% of the formulation containing 15 000–55 000 Su/mg spore count
and 63–77% mortality at 0.1% of the formulation (Loganathan and David, 2000).
At the operational level, commercial preparations of Bt have been used in India
in experimental plots as well as some private plantations. In Thailand, Bt has
been applied using fogging machines or aircraft, particularly for high value
plantations and seed orchards (Chaiglom, 1990; Hutacharern et al., 1993).