Biological Control of Insect Pests: Southeast Asian Prospects - EcoPort

346 Biological Control of Insect Pests: Southeast Asian Prospects
Comment
It has not been feasible, except for a rather more comprehensive cover of
parasitoids, to include any but the most relevant of the 2000 or so references
to T. ni in the literature. Further details can be accessed via the bibliographies
of Sutherland and Sutherland (1972, 1984) for earlier publications and via
Commonwealth Agricultural Bureau Abstracts and Lingren and Green
(1984) for much of the more recent literature.
Although T. ni is often regarded as a secondary pest of crops in its native
North America, damaging numbers, nevertheless, occur from time to time,
particularly when its natural enemies are killed or suppressed by broad
spectrum insecticides applied for associated primary pests. Predators are
often claimed to be more important than parasitoids in maintaining T. ni at
sub-economic levels.
Regrettably most, if not all, of the major predators involved lack the
degree of specificity nowadays considered necessary for introduction as
classical biological control agents. For this reason, further consideration is
restricted to the potential of parasitoids and viruses. Far more is known from
southern California than elsewhere of the parasitoid species present and their
interactions. The following discussion is thus somewhat geographically
biased and it should be borne in mind that additional species in other regions
may well have desirable characteristics, especially for their respective
climatic conditions (see later).
In addition to the egg parasitoids (e.g. Trichogramma pretiosum and
T. platneri), there are at least 4 other parasitoids worthy of serious
consideration (Copidosoma truncatellum, Hyposoter exiguae, Microgaster
brassicae (Hymenoptera) and Voria ruralis (Tachinidae)).
If host specificity considerations permit clearance of these species for
introduction to a new area, a decision must still be taken on which, if not all,
to establish. It may be useful, therefore, to review (and extend) the
information presented earlier on their attributes and interactions.
Copidosoma truncatellum oviposits into the host egg, but hatches in the
larva and takes about 36 days to develop to adult, so it is present throughout
the entire larval period of its host. Microgaster brassicae oviposits in 1st and
2nd instar T. ni larvae and requires about 14 days to develop to adult. The
mature 3rd instar parasitoid larva emerges from late 3rd or early 4th instar
hosts after feeding for about 9 days. Hyposoter exiguae commonly oviposits
into late 1st instar T. ni and emerges from late 3rd or early 4th instar hosts. It
requires about 16 days from egg to adult at 25¡C, the egg-larval period
averaging about 10 days. Voria ruralis requires about 13 days from egg to
adult. It will oviposit on all host instars, but development in most successful