Biological Control of Insect Pests: Southeast Asian Prospects - EcoPort

60 Biological Control of Insect Pests: Southeast Asian Prospects
Attempts at biological control
There have been many intentional and unintentional transfers of aphid
parasitoids, which have influenced the populations of A. craccivora and
A. gossypii in different regions of the world. However, the majority of
intentional transfers have been aimed at other target aphid pests. Some
deliberate attempts against these two species have been unsuccessful (Table
4.4.3). Overall, however, there is little doubt that, where parasitoids have
become established, the situation is better, sometimes significantly better,
than if they were not present, even if the level of control may not be as
effective as is desirable. There is little doubt that, in many regions, an
improved situation is likely to occur if additional parasitoid species are
established.
AUSTRALIA
Aphidius colemani is capable of producing rapid decreases in populations of
A. gossypii on cotton and, of carrying this to extinction in association with
high densities of Harmonia octomaculata (= Coccinella arcuata) and
Coccinella transversalis (= C. repanda) (Room and Wardhaugh 1977).
Three species of parasitoid were imported in the hope that, as polyphagous
species, they would contribute to the biological control of several species of
pest aphid. The principal target for two of the species was A. craccivora,
which is very sporadic in occurrence in Australia. It was hoped that, in the
unpredictable absence of A. craccivora, the parasitoids would continue to
breed and survive in other hosts.
Lysiphlebus testaceipes (from Aphis nerii in California) and L. fabarum
(from Greece and Turkey) were imported as biological control agents of
A. craccivora on legumes, mass reared, and released in 1982 and 1983 in
New South Wales and Victoria. Both parasitoids readily parasitised
A. craccivora, A. gossypii and some other aphid species in the laboratory.
The releases coincided with a prolonged drought during which there were no
A. craccivora available on legume crops. Releases were, therefore, made on
A. gossypii infesting Hibiscus bushes. No parasites were recovered the
following year from either A. craccivora or A. gossypii, although
L. testaceipes became established in Aphis nerii on oleander (Nerium)
(Hughes 1989). L. fabarum was not recovered. It was concluded that the
parasitoids must have been unsuitable biotypes (Carver 1984, 1989).