Biological Control of Insect Pests: Southeast Asian Prospects - EcoPort

80 Biological Control of Insect Pests: Southeast Asian Prospects
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Larvae of Aphidoletes reportedly feed exclusively as predators on aphids
and are hence more host-specific than many of the other predators:
A. aphidimyza is the best known of the cecidomyiid predators. Adults
emerge during the day from pupae in the soil. They generally fly between
sunset and sunrise. Orange-coloured eggs are laid singly or in clusters of up
to 40, usually on plants near aphid colonies. Females live up to 14 days in the
laboratory and lay about 100 eggs. These hatch after 3Ð4 days and first instar
larvae immediately seek out and attack aphids. They usually attack by
piercing a leg joint or some other joint. A toxin is perhaps injected, since the
aphid is rapidly immobilised before its body fluids are extracted. The
shrivelled bodies of some aphids remain attached to the plant by the stylet.
Larval development involves 3 instars and takes 7 to 14 days (Harris 1973).
On the other hand, Herpai (1991) reports 21 days from egg to adult (egg 3
days, larva 8 days, pupa 10 days).
Roberti (1946) gave a figure of 60 to 80 Aphis gossypii attacked per day.
Predator larvae usually drop to the soil to pupate. They construct small silk
cocoons in the top few millimetres of soil, but occasionally cocoons may be
spun on plants. Larvae pupate within a few days of cocoon construction and
adults emerge after 1Ð3 weeks depending upon temperatures. The life cycle
can be completed in about 3 weeks at temperatures above 21¡C (Harris 1973;
Herpai 1991).
Harris (1973) does not record it from A. craccivora. Two
hyperparasitoids of A. aphidimyza are known in Africa, the platygasterid
Synopeas rhanis and an unidentified braconid (Harris 1973).
There are many reports in the literature that natural enemies play an
important role in reducing (and probably regulating) the abundance of pest
aphids. More than 100 biological control programs have been mounted
against at least 26 aphid species and 48% of them have reported success
(HŒgvar and Hofsvang 1991). Twenty three species of aphidiid parasitoids
have been used in classical biological control of aphids and the parasitoids
became established in 32 out of 55 attempts (Greathead 1989). Most pest
aphids are attacked in their native range by many parasitoids and predators
and by a few pathogenic fungi. However, many of the natural enemies have
not accompanied their aphid hosts when these have spread into new regions.
Indeed, they may not even be present throughout the presumed native range
of their host. Since both the direct and indirect damage caused by aphids
seem to be proportional to their numbers, any reduction is potentially
beneficial. Even in the case of virus transmission, where the feeding (or