Biological Control of Insect Pests: Southeast Asian Prospects - EcoPort

340 Biological Control of Insect Pests: Southeast Asian Prospects
minutum from eggs collected from lettuce. In addition, the carabid beetle,
Calosoma peregrinator, fed readily on T. ni larvae (McKinney 1944).
A study in southern Texas of the loopers T. ni and Chrysodeixis
includens on a range of host plants revealed high levels (58% to 71%) of
mortality of larvae and pupae by 29 parasitoid species (Table 4.16.1) during
all but 4 months of the year, all of which existed at rather low levels (Harding
1976).
Turning to cotton in southern California, T. ni is a secondary pest and
there is good evidence that natural enemies, in particular several predators,
are mainly responsible for its generally low pest status. The 4 major
predators there are larvae of the green lacewing, Chrysoperla carnea (which
consume eggs and larvae) adults and nymphs of the bugs Geocoris pallens
and Orius tristicolor (which prey upon eggs and small larvae) and adults and
nymphs of the bug Nabis americoferus (which prey upon larvae of all sizes).
Spiders, mantids, carabids, vespids and reduviid bugs are among predators
that are also present in smaller numbers (Ehler and van den Bosch 1974;
Ehler 1977a).
Eleven species of parasitoid have been reported from T. ni on cotton, of
which the following are most important, although their combined effect is
far less than that of the predators: Trichogramma semifumatum (an egg
parasitoid), Cotesia marginiventris, Hyposoter exiguae and Microgaster
brassicae (which attack small larvae and kill hosts when of medium size),
Copidosoma truncatellum (an egg-larval parasitoid, which emerges from
large larvae or prepupae), Chelonus texanus (an egg-larval parasitoid which
kills medium sized hosts), Voria ruralis (which lays eggs on medium sized
larvae and kills large larvae or prepupae), and Patrocloides montanus (a
larval-pupal parasitoid which usually oviposits in large larvae). Copidosoma
truncatellum is polyembryonic and Voria ruralis is often gregarious (Ehler
and van den Bosch 1974).
A nuclear polyhedrosis virus was the only pathogen shown to cause T. ni
mortality, particularly late in the season at peak density of T. ni larvae, when
levels of 50 to 60% mortality have been observed.
All of the predators mentioned above are widely polyphagous. The first 4
parasitoids listed above had a restricted host range and the last 4 were host
specific in the cotton ecosystem.
Disappearance of eggs and small larvae, assumed to be due to predation,
was consistently the major mortality factor. Parasitisation of larvae by any
parasitoid seldom exceeded 30%, the exception being that by Copidosoma
truncatellum which often reached 50 to 75%. Detailed life table studies of
T. ni on cotton were reported by Ehler (1977a).