Biological Control of Insect Pests: Southeast Asian Prospects - EcoPort

338 Biological Control of Insect Pests: Southeast Asian Prospects
larvae and pupae, 7 of which were Hymenoptera and 5 Diptera (Table
4.16.1). These produced an average of 38.9% mortality, with a maximum of
66.7% in late autumn. The tachinid, Voria ruralis, was the dominant
parasitoid, especially during autumn and winter months. The ichneumon,
Hyposoter exiguae, and the encyrtid, Copidosoma truncatellum, occurred
most commonly during the summer and autumn months, when the latter was
associated with a nuclear polyhedrosis virus. Together (and particularly the
virus) they were responsible for most of the 60% larval mortality. Pupal
mortality was low (2.0%) and was due to the pteromalid Pediobius
sexdentatus (Oatman and Platner 1969). Also in southern California, Clancy
(1969) reared 5 wasps and 5 tachinid flies (Table 4.16.1) from T. ni larvae
collected from annual weeds (Malva sp., Chenopodium sp.), mustard, tree
tobacco (Nicotiana glauca) and lucerne. The fly, Voria ruralis, was the most
abundant parasitoid in autumn and winter and Copidosoma truncatellum the
most important wasp, the total parasitisation from all species ranging from
29.5% to 41.1%. A nuclear polyhedrosis virus killed 70.9% of larvae
collected in summer from weeds and 63.8% from lucerne (Table 4.16.6).
The mortality caused by the various natural enemies varied according to the
season and host plant.
Henneberry et al. (1991) recorded 12 species of parasitoid from larvae of
the loopers T. ni and Autographa californica on lettuce, lucerne, sugarbeet
and cotton in southern California. Of these, the braconid Microgaster
brassicae (30%) Voria ruralis (23%) and Copidosoma truncatellum (23%)
were the most abundant, with parasitisation rates ranging from 0% to 91.8%
according to season and crop. Average mortality from viral infection ranged
between 0.6% and 7.2%, also depending upon the crop.
Thirteen parasitoid species reared from T. ni on tomatoes in southern
California (Table 4.16.1) caused mean parasitisation rates of larvae of 51.4%
and 70.5% and of eggs of 24.6% and 53.4% respectively in two successive
years. Hyposoter exiguae and Copidosoma truncatellum were the most
abundant larval parasitoids and Trichogramma pretiosum the most
important species attacking eggs. The data on population trends and
percentage parasitisation suggested that there was a density-dependent
relationship between T. ni and its parasite complex on tomato (Oatman et al.
1983a).
In Arizona, the most abundant parasitoid of T. ni larvae collected from
weeds and cultivated crops was Voria ruralis, which was present throughout
the year, with peak abundance (up to 100%) in late autumn and winter
(McKinney 1944; Butler 1958b; Brubaker 1968). Five wasps and 1 tachinid
fly were reared from larvae, 1 tachinid from pupae and Trichogramma