Biological Control of Insect Pests: Southeast Asian Prospects - EcoPort

70 Biological Control of Insect Pests: Southeast Asian Prospects
VIETNAM
A. gossypii was one of four aphids surveyed for parasitoids by Starù and
Zelenù (1983), but the number of aphidiid species found (2) was surprisingly
low. Lipolexis scutellaris was commoner than Lysiphlebia mirzai. The
former parasitises a number of other Aphis species, including Aphis
spiraecola (= A. citricola), A. craccivora and A. nerii. Some unidentified
aphelinid parasitoids were also present.
Starù and Zelenù (1983) suggest that Lipolexis scutellaris may be a
valuable species for transfer elsewhere and also that Vietnam would benefit
from the introduction of additional parasitoid species.
The major parasitoid species
General features of the Aphidiidae
Different populations of many Aphidiidae have differing biological
properties and are often known as biotypes, i.e. contrasting groups, each
consisting of individuals of the same species. Biotypes are recognised by
biological function rather than morphology and consist of those individuals
that behave similarly as far as our immediate interests are concerned
(Mackauer and Way 1976).
The members of this family attack aphids exclusively and are probably
the most commonly observed cause of aphid mortality in the field. In
Europe, many, if not all, aphid colonies come to include some mummified
individuals (i.e. dead aphids containing a fully-grown parasitoid larva or
pupa) (Starù 1970). Aphidiidae may hibernate as prepupae within host
mummies. All are solitary endoparasitoids. All aphid stages are attacked
except the eggs, but alatae are least often attacked. The parasitoid egg is
usually inserted anywhere in the aphid abdomen. The preferred aphid larval
instar varies with the parasitoid species, but younger instars are usually
chosen. If adult aphids are parasitised the parasitoid larva may not complete
its development before the insect dies, so that the parasitoid perishes also.
Oviposition into an aphid does not ensure the successful development of a
parasitoid, since the host may be unsuitable or it may already be parasitised:
defence and immune responses are common. However parasitised hosts are
usually distinguished by the parasitoid and receive no further eggs.
If an aphid is parasitised during the last larval instar, a mummy is formed
after it moults to the adult. The first and second instars of aphidiid
parasitoids generally feed on haemolymph, but the last instar attacks the
alimentary canal and other organs, ultimately killing its host. The parasitoid
larva then spins a cocoon and pupates inside the empty aphid skin. The adult
emerges through a small circular hole usually cut dorsally or apically near