Pest Management in Miombo Fruit Trees - Indigenous Fruit Trees in the Tropics: Domestication, Utilization and Commercialization - page 384

common defoliator of Sclerocarya birrea , are attacked by eupelmid wasps
Anastatus spp., Mesocomys pulchriceps and Mesocomys vuilleti in South Africa
(Van Den Berg, 1990). Similarly, Imbrasia belina , another defoliator of
Sclerocarya birrea , suffers up to 40% mortality from the egg parasitoid
Mesocomys pulchriceps in Botswana (Ditlhogo, 1996). Several of the sap-
sucking insects, especially scales, mealy bugs and aphids, are attacked by a
large number of native parasitoids, some of which have been successfully used
in the biological control of fruit trees pests in Africa (Wakgari, 2001; Lux et al .,
2003).
Predatory insects also play a significant role in the natural control of pest
species in southern Africa (Dirorimwe, 1996; Sileshi et al ., 2001). Among the
ladybird beetles, Alesia , Cheilomenes , Chilocorus , Exochomus , Hippodamia ,
Hyperaspis and Platynaspis spp. are the common predators of aphids and scale
insects (Lee, 1971). Syrphid flies, especially Paragus sp., Xanthogramma
aegyptium and X. pfeifferi , prey on aphids attacking fruit trees and crop plants
in Malawi and Zimbabwe (Lee, 1971; Dirorimwe, 1996). Various bugs and
carabid beetles can prey on a wide range of insects. The reduviid bugs
Rhinocoris spp. and pentatomid bugs Afrius , Glypsus , Macrorhaphis and
Mecosoma spp. feed on a number of beetles and caterpillars (Sileshi et al .,
2001), defoliating various fruit tree species in the miombo (G. Sileshi,
unpublished results). The reduviid bugs Cosmolestes pictus and Callilestes
gracilis prey heavily on Gonometa species, defoliators of Parinari curatelifolia in
Botswana (Hartland-Rowe, 1993). Although biological control strategies are
more often linked to the use of specific natural enemies, generalist predators
undoubtedly play a significant role in limiting pest populations, particularly at
low prey density (Van Driesche and Bellows, 1996). The populations of such
organisms can sometimes be concentrated in the orchard and their egg
deposition increased by spraying solutions of attractants such as meat meal or
fish meal, sucrose, molasses and brewers yeast in the field (Sileshi et al ., 2001).
Birds of prey (e.g. owls and buzzards) and snakes are known to keep the
population of rodents to a tolerable level in plantations and orchards. Where
the habitat preferences of the predators are known, cultural practices may also
be manipulated to favour their activity. This includes less disruptive weed
control, orchard floor and habitat management practices and judicious use of
pesticides.
Plant resistance
One of the most significant improvements in the management of forest trees
involves seed-source selection. In the early days, seeds were collected with little
regard for tree form, growth rate or disease resistance, resulting in inferior
seedlings. Today, orchards comprise clones selected for desirable tree growth
and pest resistance traits. This practice has not yet gained wide application in
indigenous fruits of the miombo. In future, seed orchard clones should be
meticulously selected from field sources, and their subsequent progeny carefully
evaluated on a variety of field planting sites. Choice of scion and rootstock also
greatly influences pest management as both vary in their resistance to many