Biological Control of Insect Pests: Southeast Asian Prospects - EcoPort

Damage
4.11
Leucinodes orbonalis
189
All stages of eggplant are attacked by L. orbonalis,
which is regarded as one
of its major insect pests. Larvae bore into the tender shoots of both seedlings
and after transplantation older plants, causing wilting and death of the
growing tips. Later, they bore into flower buds and fruits. The damaged buds
are shed and the fruits carry circular holes, sometimes plugged with frass.
Such fruits are unmarketable. The yield loss varies with location and season
and is greatest when temperature and humidity is high. Losses range from 20
to 60% (Krishnaiah 1980; Dhankar 1988, Roy and Pande 1994) or even
higher (Akhtar and Khawaja 1973; Lal 1991). It is reported that Vitamin C in
bored fruit can be reduced by 60% (Hami 1955).
There is an extensive literature dealing with the screening, mainly in
India, for resistance of eggplant cultivars to L. orbonalis.
Some cultivars are
far less damaged than others, although no information is available on the
genes involved. The less susceptible cultivars generally have one or more
morphological characteristics, including compact vascular bundles in a thick
layer, lignified cells and less area of pith in the shoots, tougher fruit skin and
a tight calyx to hinder larval entry. Biochemical factors involved include a
low protein and sugar content in resistant genotypes and a higher silica and
crude fibre content in the shoots, which adversely affects growth rate, pupal
period, survival, sex ratio and fecundity. The wild relatives of Solanum
melongena that are not attacked by L. orbonalis often have a high alkaloid
content, which may be responsible, but this attribute would not be desirable
in an edible product (Dhankar 1988).
Natural enemies
Table 4.11.2 lists the natural enemies of L. orbonalis.
It is striking that most
are from India and Sri Lanka, that the records from Malaysia and the
Philippines are the only ones from Southeast Asia and that the species there
have not been reported elsewhere. Although it is possible that some of the
Indian and Sri Lankan species have a restricted distribution, the lack of
records from elsewhere probably means that the necessary investigations
have not been carried out.