Agriculture Reference
In-Depth Information
maximum number of aphids per 10 plants was 755, which was counted on
untreated plots. Soap spray was less effective, while kerosene caused
irreversible phytotoxicity. Infestation levels increased with advancing maturity
of the crop, rising dramatically near crop maturity. Plant damage due to aphids
was also visually assessed and the second lowest damage was recorded on hot
pepper treated plots. Furthermore, pirimicarb gave 93% and hot pepper 54%
more grain yield than no treatment. Percentage parasitism (~40%) of aphids
was greater on pirimicarb treated plots than on other treatments (<20%). The
low percentage on pirimicarb treated plots must be because the aphids are less
in number (density-dependent scenario) and parasitism is calculated on the
basis of the total number of aphids counted. Parasitism was essentially a late
season occurrence. Despite the high prevalence of parasitism, parasitoids
could not spare the crop from destruction because they just acted late.
However, their presence is still valued because otherwise these crops would
have been abandoned altogether. More interestingly, predatory coccinellids
were more on hot pepper and garlic treated plots than on pirimicarb treated
plots (Wale, 2004). Grain yield was positively correlated with the level of
aphid parasitism, coccinelid number and number of pods per plant and
strongly negatively with aphid density. Because the objective of the
experiment was finding good botanical against pea aphids, hot pepper was
found better candidate.
S
UMMARY AND
C
ONCLUSION
Biology and ecology studies show that lentil is the most suitable of the
legumes for the development of the pea aphid. Thus lentils may not be good
choice of crop in places where pea aphids is a problem. It is, however, suitable
for use in mass rearing of aphids for resistant variety selection or for natural
enemy mass production. A prolonged developmental period and short
reproductive period of the aphid may be used as criteria for resistant crop
variety selection.
Pea aphids infested the cultivated forage crop, vetch, the wild legume,
clover, and the perennial tree, pigeon pea, but not the cultivated lupine and
alfalfa. Causes may include differences in aphid biotype that have developed
specifically to each host plant, differences in secondary metabolites or
alkaloids that deter pests or the level of nitrogen content of the plants. Given
the limited research attention given to this group of pests in Ethiopia, the
studies so far conducted prompt us to ask more questions than give definitive
