Biological Control of Insect Pests: Southeast Asian Prospects - EcoPort

210 Biological Control of Insect Pests: Southeast Asian Prospects
Additional strains were later liberated of what, at the time, was believed to be
T. basalis. These originated from the West Indies (1953), Italy (1956) and
Pakistan (1961). However, doubt has been cast on the specific identity of the
Italian material, although T. basalis is known to occur there. The Pakistan
material, originally identified as T. basalis (but probably containing two
species) has recently been shown (Clarke 1993a) to have consisted mainly of
a new species Trissolcus crypticus. This bred readily in N. viridula eggs in
the laboratory and, later, was widely distributed in Australia and Hawaii.
However, T. crypticus has not been reported since in field collections.
For many years up to the mid 1960s N. viridula was a very common and
serious pest in the Canberra district, damaging tomatoes and beans in
particular. This situation changed dramatically following the liberation of
the material from Pakistan (presumably both T. basalis and T. crypticus)
and, since then, N. viridula has become a very uncommon insect, appearing
only in extremely limited numbers late in the season and only every few
years. A great improvement also resulted about the same time in other
subcoastal eastern cultivated areas, credited by Ratcliffe (1965) also to the
liberation of material from Pakistan.
However, since T. crypticus apparently did not become established its
role, if any, in the changed situation is unclear. It is not known whether any
cross mating with T. basalis might have occurred, which might have
resulted in greater adaptability of T. basalis to the Canberra environment.
The continuing very low abundance of N. viridula is possibly attributable to
a heavy attack on its eggs by a resident population of T. basalis which is
maintained on native pentatomid hosts, of which there are several (see later).