Contents - LAC Biosafety

10.17 Tectona grandis (Lamiaceae) 323
Thus it is now well established that H. puera causes significant economic loss
in teak plantations.
In addition to loss in volume increment, defoliation may cause dieback of the
leading shoot of saplings and consequent forking. Champion (1934) reported
that repeated heavy defoliation of saplings led to forking. Khan and Chatterjee
(1944) observed damage to 52% of the saplings in a three-year-old plantation at
Tithimatty in Karnataka, India and attributed it to heavy defoliation by Eutectona
machaeralis. Incidence of dieback in 43% of saplings, with incidence as high as
91–99% in some plots (267–333 trees per plot), was reported in a three-year-old
plantation in Kerala, India (Nair et al., 1985). However, heavy incidence of
terminal bud damage is a rare event. In young plantations at Nilambur in Kerala,
India, although defoliation occurred every year, dieback of leading shoot
occurred only in two out of seven years of observation. Detailed observations and
artificial defoliation experiments led Nair et al. (1985) to conclude that leading
shoot damage occurs only under a unique combination of conditions, leading to
repeated destruction of buds. Feeding on the terminal bud by the pyralid,
Eutectona machaeralis is perhaps more important in causing dieback of the leading
shoot. They also found that permanent forking occurred in only about 10% of
the saplings that suffered leading shoot damage because in many cases one
of the shoots took over as the leader.
Natural enemies H. puera has a large number of natural enemies – about
45 species of parasitoids (3 of eggs, 15 of larvae and 26 of pupae), 108 predators
(mostly of larvae: 27 insects, 31 spiders and 50 birds), 1 nematode and
7 pathogens. Most records are from India and the neighbouring countries
(Pakistan, Bangladesh, Myanmar and Sri Lanka). Further details are given under
the section on control.
Control Control options for H. puera in teak plantations have been
reviewed by Nair (1986a, 2001b).
Biological control with parasitoids and predators Early control attempts relied
on the many natural enemies of the insect, particularly the insect parasitoids.
Based on detailed studies in India and Myanmar on the parasitoids of the two
major defoliators, H. puera and Eutectona machaeralis (see below), their alternative
insect hosts and the plant hosts of these caterpillars, as early as 1934 Beeson
(1934) developed a package of practices for biological control of the two pests,
by adopting silvicultural measures to conserve their natural enemies. The theoretical
foundation was that the pests could be kept in check by encouraging the
endemic insect parasitoids and predators, through ensuring the presence, in the
surroundings, of plants that supported their alternative caterpillar hosts or prey.