Biological Control of Insect Pests: Southeast Asian Prospects - EcoPort

4.16
Trichoplusia ni
321
describing laboratory experiments in which parasitoids, predators and/or
pathogens have been tested on T. ni eggs or larvae. It is often not possible to
determine from these accounts whether or not the natural enemy involved
has been found attacking eggs or larvae of T. ni in the field and hence
possibly a useful control agent. If T. ni is susceptible to the agent in the
laboratory, such records have often been included, although behavioural or
other factors might well influence its effectiveness under field conditions.
No attempt has been made to include reports of all of the minor natural
enemies, especially in the earlier literature.
As will become clearer when the situation is discussed later, many
parasitoids (Table 4.16.1), predators (Table 4.16.2) and pathogens (Table
4.16.3) have been recorded attacking the cabbage looper in the field and/or
in the laboratory and there is little doubt that looper populations are
frequently kept at sub-economic levels by their action. A number of the
natural enemies recorded are not widespread in distribution and appear to be
incidental records.
Many of the predators are widely polyphagous and attack insect pests in
several orders, although a few are considerably more selective than that.
Parasitoids, on the other hand, tend to be significantly less polyphagous than
predators and some appear to be confined to T. ni,
at least in certain crops.
Where parasitoids have a relatively broad host range, available records
indicate that this extends mainly to larvae of other Lepidoptera (generally
pest species) in the same crop situation. The extent to which it extends also to
non-pest, non-target species is not documented. Nevertheless, there are
several species that merit serious consideration as candidates for classical
biological control.
All of the Trichogramma species oviposit and develop in the host egg. A
few others (eg. Copidosoma truncatellum,
Chelonus blackburni, Chelonus
insularis)
oviposit in the egg and develop in the host larva; and the remainder
are larval and/or pupal parasitoids.
Naturally occurring epizootics of nuclear polyhedrosis virus in medium
to large T. ni larvae are considered to be the major mortality factor affecting
them on cabbage in summer and autumn in southern California (Oatman and
Platner 1969), on broccoli in Virginia (Hofmaster 1961) and on cabbage in
North Carolina (Elsey and Rabb 1970b). Polyhedrosis was seldom a major
factor on cotton in southern California (Ehler 1977b), although outbreaks
did occur late in the season or at times of high T. ni abundance (Ehler and van
den Bosch 1974).
Although the mortality produced is probably not significant, birds and
bats are known to feed on moths in flight; and earwigs on adults resting
beneath host plants (McKinney 1944; Sutherland 1966).