Agriculture Reference
In-Depth Information
However, these grain crops are not without constraints in the country. The
pea aphid,
Acyrthosiphon pisum
(Harris) (Aphididae: Homoptera), among
others, is a major pest that is pushing pulses out of production. It feeds on a
wide range of plants that belong to 14 genera, the major ones being
Coronilla,
Lens, Lotus, Medicago, Melilotus, Pisum, and Vigna
(Ellsbury and Nielson,
1981). Pea aphids attack all kinds of peas (garden and field peas) (
Pisum
sativum
), alfalfa (
Medicago sativa
), clover (
Trifolium
sp.), and other
leguminous crops except those in the genus Phaseolus (Ellsbury and Nielson,
1981; Davidson and Lyon, 1987). Lucerne (
Medicago sativa),
pea
(Pisumsativum),
clover
(Trifoliumruepellanium),
egg-plant
(Solannum
melongena),
vetch
(Vicia
spp
) and
broad bean
(Vicia fabae)
are heavily
attacked (Archibald, 1979). It infests Lucerne to such an extent that the ground
turns white due to exuviae (Archibald, 1979).
In addition to the irreversible damage due to direct plant sap sucking, pea
aphids transmit viral diseases that cause total crop loss. Losses in the
production of peas probably exceed that caused by any other pest of peas
(Davidson and Lyon, 1987).
Pea aphid is distributed throughout North America (Davidson and Lyon,
1987), Europe, Asia and the cooler areas of East Africa (Autrique et al., 1989).
Host variety and aphid biotype are important for the host and aphid association
(Bournoville et al., 2000; Caillaud and Via, 2000; Morgan et al., 2001).
Prior to 1983 when Crowe and Ali (1983) published a checklist of 64
species of aphids recorded in Ethiopia,
A. pisum
was reported but was not
considered important. Abate et al. (1982) and Ali and Gebremedhin (1990)
have reported its minor pest status in earlier surveys in Ethiopia. Nevertheless,
the pest has quickly become a key pest of legumes since 1983/84 season (Ali
and Gebremedhin, 1990). Ever since it has been widening its geographical
coverage and the range of plant species attacked.
In Ethiopia, the pea aphid has a holocyclic life cycle, i.e., it reproduces
parthenogentically without producing sexual forms, which is typical of tropical
and subtropical species (Cardona et al., 1984; Ali and Gebremedhin, 1990).
Viviparity permits rapid exploitation of the host plant as its parthenogenetic
multiplication rate, without fertilization, is potentially enormous. In temperate
areas, pea aphids reproduce both sexually (via eggs) during the winter and
parthenogenetically during the summer (Davidson and Lyon, 1987).
Yield loss caused by pea aphids on field pea can be as high as 37% at
some regions (Gebremedhin, 1990). To date, total (100%) crop failures have
become common in many parts of Ethiopia (Andarge and Berhan, 1998).
Growers in Zema valley of West Gojam zone, Ethiopia, for example, have quit
