Contents - LAC Biosafety

346 Insect pests in plantations: case studies
silk and pupated within. This appears to be the typical pupation behaviour.
Most other cossids are known to pupate within a chamber made in the larval
gallery itself but in Cossus cossus, infesting hardwood trees in Europe and
North America, pupation may occur either within the tunnel, near the entrance,
in a silken cocoon or at the base of the host tree in an earthen cocoon (Browne,
1968). Bhandari and Upadhyay (1986) who studied the biology of A. cadambae
infesting the root collar region of young trees of Diospyros melanoxylon,
mentioned that wood particles are embedded in the pupal cocoon along with
faecal pellets, indicating that pupation occurred in the tunnel itself, although
this was not explicitly stated. More detailed observations are necessary on the
pupation behaviour of this insect infesting different hosts. The average pupal
period is about 11 days, and before moth emergence the pupa wriggles to the
soil surface and projects out.
A. cadambae has overlapping generations. In light trap collections from a
heavily infested teak plantation in Kerala, India, the moths were most abundant
during May–June and August–October, but small numbers were present
throughout the year. This somewhat reflects the rainfall-linked pupation
pattern. Kerala receives two monsoons per year, the first starting in early June
and the second in mid-October, with pre-monsoon showers occurring earlier.
It is not clear whether the moths collected during the drier period of December–
March are indicative of pupation occurring also during the dry period or of
dormancy of the pupae that were formed earlier (Mathew, 1990).
Timber quality is degraded by A. cadambae infestation. The larval tunnel
follows a radial, zigzag course and extends into the heartwood. Because of
repeated attack of infested trees, borer holes often occur in a cluster (Fig. 10.43)
and these clusters extend throughout the bole. Consequently, planks cut from
heavily infested logs will have numerous holes. In addition to such damage,
heavily infested trees die in the course of time, possibly aided by associated fungi
(Mathew and Rugmini, 1996). The fungus Phialophora richardsii has been isolated
from borer-infested wood. Studies in Kerala (Mathew et al., 1989) showed that
in the initial phase of attack of a plantation, the infestation is clumped.
In subsequent years, further deterioration of the already infested trees occurs
as a result of reinfestation and there is slow spread of infestation to other trees.
A representative survey of the teak plantations of Kerala showed that 4% of
the plantations had A. cadambae infestation, with 2–40% of the trees within the
plantation affected. Trees below 15 years of age were not infested. In affected
pockets, the proportion of infested trees increased with age of the trees,
obviously due to repeated infestation of the same trees.
Other tree species on which A. cadambae has been recorded are Diospyros
melanoxylon (Bhandari and Upadhyay, 1986), Grewia tiliaefolia, Terminalia bellerica