Contents - LAC Biosafety

10.17 Tectona grandis (Lamiaceae) 333
solution or diluted honey. Eggs are laid singly on teak leaves, usually on the
underside. Average fecundity ranges between 203 and 374, and maximum
between 500 and 550 (Beeson, 1941; Wu et al., 1979; Patil and Thontadarya,
1987a). The oviposition period is 1–2 weeks.
There are five larval instars. The first and second instars feed superficially
on the leaf, under protection of strands of silk. Third to fifth instars eat out
the entire leaf tissue between the fine network of veins, and thus skeletonize the
leaf. Under natural conditions, the larvae feed mainly on older leaves, but given
the choice they prefer younger leaves, on which the larval growth is faster, the
pupae produced are heavier and the rate of survival is higher (Beeson, 1941;
Roychoudhury et al., 1995b, 1997a). The larval shelter on the leaf is characteristic.
The larva makes a shelter web and an escape hole on the leaf that permits it to
retreat quickly when disturbed to the opposite side of the leaf and drop down on
a thread of silk. Pupation occurs on green leaf or on fallen leaf, under cover of a
stronger shelter web with small, oval holes round the edges and an emergence
hole at one edge. The males live for 9–15 days and females 12–20 days when
provided with diluted honey as food.
The duration of the developmental period varies according to the climate.
At Nilambur, in Kerala, India, where there is no distinct winter season,
the normal developmental period was 2–3 days for eggs, 12–20 days for larva and
5–8 days for pupa (Beeson, 1941). Including a pre-oviposition period of 3 days,
the total life cycle lasts from 23–31 days. Thus in field cages, 14 complete
generations and a partial 15th were possible per year. At Dehra Dun in north
India, where there is a winter season, the larval period is 12–14 days from
March to October, but between November and March the larva is reported to
enter hibernation which may last for 140–150 days and the pupal period may
be prolonged to 27 days (Beeson, 1941). Consequently only 10 generations are
completed per year. At Dharwad in Karnataka, India, where there is a mild
winter, a variable proportion of larvae enter hibernation in the pre-pupal stage
during the winter months. This was shown by Patil and Thontadarya (1986)
who collected 30 mature larvae from the field at weekly intervals and
maintained them on teak leaves in a field laboratory. Between mid-October
and mid-February, 3–67% of the insects entered diapause, with a mean of 38%;
the highest was in November–December. Although Patil and Thontadarya (1986)
called this phenomenon diapause, since it is promptly terminated at higher
temperature it is more similar to hibernation. In laboratory experiments, Patil
and Thontadarya (1987b) showed that the majority of mature larvae exposed to
15 °C or20°Centered hibernation in the pre-pupal stage. Exposure of eggs or
early larval instars to lower temperatures did not induce pre-pupal hibernation.
Termination of hibernation depended on the temperature; it occurred in about