Biological Control of Insect Pests: Southeast Asian Prospects - EcoPort

4.12 Nezara viridula 209
attracted to the cis isomer provided the major selection pressure leading to
the present N. viridula populations having predominantly the trans isomer in
their pheromone mix. Perhaps in parallel, in the 200 years or so of interaction
between N. viridula and T. pennipes in tropical America, N. viridula has
evolved a shorter pre-oviposition period and a longer developmental period
than an Italian population (Hokkanen and Pimentel 1984; Aldrich et al.
1989). At all events, at least two distinct pheromone strains of N. viridula
can now be distinguished, based on the presence or absence in the volatile
secretions of the cuticle of cis-(z)-a-bisobolene epoxide. Mature N. viridula
males of one population from Brazil produce the trans, but not the cis isomer
(Baker et al. 1987), whereas males from 2 other populations do in ratios of
2.28:1 and 4.67:1 respectively (Aldrich et al. 1993), similar to males from
southern USA which produce the trans and cis isomers in a 3:1 ratio (Aldrich
et al. 1987) and those from Southern France in a 2:1 ratio (Baker et al. 1987).
A quite different, but somewhat analogous situation, occurs with the
hymenopteran Trissolcus basalis. A short chain unsaturated aldehyde, (E)-
2-decenal present in the defensive scent produced in the adult N. viridula
metathoracic gland (Gilby and Waterhouse 1965) is attractive to female
T. basalis. A different compound, secreted on the eggs by the ovipositing
female N. viridula, attracts female T. basalis to the egg raft (Mattiacci et al.
1991, 1993). This compound is produced in the bug ovary and serves as an
adhesive for attaching the eggs to the oviposition substrate. The adhesive
and the material(s) responsible for the kairomone activity were partly
soluble in water and completely in acetone and elicited recognition
behaviour from T. basalis females when applied to glass beads. The
adhesive appears to be a mucopolysaccharide-protein complex (Bin et al.
1993).
Attempts at biological control
Early attempts at biological control were made chiefly in Australia and the
Pacific, countries where the introduction of the bug was comparatively
recent, but many other countries have been involved in more recent times.
AUSTRALIA
N. viridula was first reported in Australia in 1916 and soon became a
widespread and serious pest. In 1933 the scelionid wasp Trissolcus basalis
was introduced from Egypt into Western Australia (Table 4.12.2) where it
readily became established and produced a great reduction in the pest status
of the green vegetable bug. From Western Australia the parasitoid was
distributed widely throughout south and southeastern Australia, making a
considerable impact on the bug, except in cultivated areas in inland eastern
Australia, where the cold winters affected its abundance (Wilson 1960).