Pest Management in Miombo Fruit Trees - Indigenous Fruit Trees in the Tropics: Domestication, Utilization and Commercialization - page 383

Damage by rodents can be reduced by managing understorey plant growth.
Orchard sanitation is one of the major cultural control methods for fruit flies.
This may include collecting and destroying all fallen fruits by burying (about
1-2 feet deep) or burning them immediately. Such a method, however, is very
labour-demanding, since it is effective only when the fruit is collected regularly
twice a week throughout the period of fruit maturity and ripening. If fallen fruits
are left in the orchard, insects such as fruit fly larvae will crawl out of the fruits,
pupate in the soil, emerge, and infest the fruits remaining in the orchard.
Biological agents
Biological agents that control pests of fruits in the field include antagonists such
as mycorrhizas, and pathogenic, parasitic and predatory organisms. Mycorrhizas
have been proved to increase the resistance of trees to infection by pathogenic
fungi (Marx, 1972; Wheeler, 1992), including various Pythium and Fusarium
species (Gunjal and Patil, 1992) and endoparasitic nematodes (Duponnois et
al ., 2000; Borowicz, 2001). For example, ectomycorrhizal fungi inhibit Douglas
fir root rot, a condition cited as killing more trees than clear-cutting does
(Wheeler, 1992). Possible modes of action include the production of antibiotics
by the mycorrhizal fungi, and stimulation of host defence mechanisms and the
physical barrier by ectomycorrhizae (Marx, 1972; Duponnois et al ., 2000).
Mycorrhizae are known to affect the growth of Uapaca kirkiana (Mwamba,
1995), and if the seedlings are inoculated with mycorrhizas in the nursery 100%
survival following field planting is possible (Maghembe et al ., 1994).
Naturally occurring pathogenic organisms that kill insects include viruses,
bacteria, fungi and nematodes. Recently, biopesticides have been shown to
offer alternatives to chemical methods of pest management in forestry and
horticulture. In relation to the many orders of insects and other invertebrate
pests of forestry, it is only the defoliators, particularly caterpillars and beetles,
that have been targeted by mainstream microbial insecticides (Evans, 1999).
Commercial preparations of granulosis viruses and bacteria such as Bacillus
thuringiensis are available for the control of caterpillars. Commercial
preparations of naturally occurring fungi such as Metarhizium and Beauveria
have also been shown to be effective against termites (Maniania et al ., 2002)
and fruit fly larvae (Lux et al ., 2003). Biopesticides are host-specific,
environmentally friendly and compatible with other control options. However,
they are not easily accessible to small-scale farmers.
In their native habitat, defoliator insects are controlled by parasitic insects
that attack the egg, larval or adult stage. For example, an unidentified braconid
wasp parasitizes Euproctis rufopunctata on Uapaca kirkiana , Adansonia digitata
and Ziziphus mauritiana in the field (G. Sileshi, unpublished results). The
ichneumonid wasp Charops sp. attacks Phalanta phalantha on Flacourtia indica
in eastern Zambia. Coccygodes sp. and Goryphus sp. attack Niphadolepis
alianta on Annona (Lee, 1971). The tachinid flies Carcelia illota , Drino
imberbis , D. inconspicua and Tachina fallax parasitize Xanthodes graellsii on
Azanza (Lee, 1971). Encyrtid wasps attack mealybugs and scale insects, while
some braconid wasps attack various aphids. Eggs of Argema mimosae , a