Biological Control of Insect Pests: Southeast Asian Prospects - EcoPort

4.12
Nezara viridula
201
which constitute the presumed area of origin of the green vegetable bug. Egg
parasitoids are the most numerous and all are Hymenoptera, whereas
nymphal and adult parasitoids are, with one exception, all Diptera. Two
hyperparasitoids of the major egg parasitoid Trissolcus basalis are known
from Australia, (both are species of Acroclissoides:
Clarke and Seymour
1992) and one hyperparasitoid of the fly Trichopoda pennipes from Hawaii
( Exoristobia philippinensis:
Davis and Krauss 1965). Predators are not dealt
with as all are known to be, or suspected as being, widely polyphagous and
hence unlikely to be approved for introduction to new areas. Nevertheless,
they play a significant role in maintaining N. viridula populations at low
levels. For example, in one study in soybeans in Louisiana, Stam et al.
(1987) found 18 insect and 6 spider species to be predators and that they
were responsible for 33.6% of the total mortality of N. viridula that occurred
from egg to adult.
The Scelionidae is the most important of the six families of
hymenopterous egg parasitoids. In it Trissolcus basalis is not only the most
important species, but also the most widespread. It attacks the eggs of a
number of other pentatomids, but appears to have a preference for
N. viridula:
it is the dominant parasitoid of N. viridula eggs wherever it
occurs. Many other species are listed, in particular in the genera Trissolcus,
Telenomus, Ooencyrtus and Gryon,
but a number appear to have no close
relationship with N. viridula and are unlikely to be of value as potential
biological control agents. Some drought-resistant species from the
Mediterranean may prove useful. The better known of the more promising
species are discussed later.
The tachinid parasitoids of adult N. viridula also oviposit on the cuticle
of 4th and 5th instar nymphs. Often these eggs are shed before hatching
along with the cuticle at moulting but, if hatching and penetration of the bug
occurs, the parasitoid larva matures in the adult. More of the species of
tachinids are native to South America than elsewhere. They were clearly
dependent upon other pentatomids before the arrival of N. viridula,
but
several now appear to have a preference for it. The most promising of the
three tachinid parasitoids occuring in the Ethiopian region is the widespread
Bogosia antinorii,
which is known only from N. viridula (van Emden 1945;
Barraclough 1985).
A picorna-like and a toti-like virus are known from N. viridula
(Williamson and Wechmar 1992, 1995).