Contents - LAC Biosafety

10.9 Gmelina arborea (Lamiaceae) 255
Life history The biology of C. leayana has been studied in detail by
Garthwaite (1939) and Ahmad and Sen-Sarma (1990). Under favourable
temperatures, the life cycle is completed in 35–50 days, but third generation
adults enter hibernation in winter. Eggs are laid in clusters of about 10–100
(average 68), on the under-surface of leaf or on tender stem and are covered by a
sticky, frothy secretion which solidifies to form a domed, brownish ootheca.
The oviposition period may range up to 45 days, with an average fecundity of 874
(Ahmad and Sen-Sarma, 1990). There are five larval instars. The larvae are
gregarious. The early instars feed by scraping the surface of the leaf but later
instars and the adult feed by making large, irregular holes on the leaf.
Even young shoots are eaten up when the larval density is high. The larval period
can be completed in about 18 days under optimal conditions. Pupation occurs on
the leaf itself; before pupation the full-grown larva fastens itself to the leaf
by the first three abdominal segments.
Seasonal incidence At Dehra Dun, in northern India, the beetles appear
in May and pass through three generations, third generation beetles undergoing
a quiescent period of about eight months from September–October to May.
During this period, the beetles hide in cracks and holes under the dead bark of
standing trees, in hollow bamboos, in grass clumps and thatches and in curled
dry leaves on the ground (Beeson, 1941). Prior to the resting period, the beetles
may disperse up to 2 km away from the plantations in search of suitable shelters.
The period of inactivity, generally called hibernation and aestivation, depends
on the weather, and its termination coincides with the appearance of new
flushes on the host tree after a period of leaflessness in summer, and may vary
from region to region.
Host range and geographical distribution There are no records of other hosts
for C. leayana. The insect has been recorded in India, Bangladesh, Myanmar and
Thailand. In India, it is prevalent in the northern region but also occurs in
central and southern regions (Meshram et al., 2001; Nair and Mathew, 1988). In a
review paper, Suratmo (1996) lists C. leayana as a pest of G. arborea in Indonesia,
where the tree is exotic, but gives no details of the place of occurrence. Since
other authors have not listed the insect as occurring in Indonesia, this report
needs confirmation (Nair, 2000). There are no reports of its occurrence in Africa
or Brazil, where there are extensive exotic plantations of Gmelina.
Impact Both the adult and immature stages of C. leayana feed on leaves
and, when the population density is high, also on shoots. Heavy attack causes
total defoliation and drying up of the leader shoots in young trees, leading to
severe growth retardation. With two or more consecutive complete defoliations