The Relative Importance of Three Cabbage Aphid Species (Brevicoryne Brassicae, Lipaphis Erysimi; Myzus Persicae) and Their Parasitoid Complex in Kenya.
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Date
2000
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Addis Ababa
Abstract
Studies on the relative importance of the three known species of cabbage
aphids (Brevicoryne brassicae (Linneaus), Myzus persicae (Sulz) and Upaphis
erysimi (Kaltenbach)) and their parasitoid complex in Kenya were carried out.
The studies involved farmers' fields' surveys and interviews and also field
experiments conducted at the Jomo Kenyatta University of Agriculture and
technology (JKUAT) Research and Production Department land and in a
farmer's field at Limuru. Gloria F1 hybrid was sown at JKUAT while
Copenhagen Market variety was sown at Limuru.
The field experiments were conducted in a Completely Randomized Block
Design (CRBD) involving three treatments and a control, with three repl icates
each. The treatments comprised of applications of: - Lambda-Cyhalothrin
(Karate; Bacillus thuringiensis Berliner (Bt.) var. Kurstaki toxin (Dipel 2x) that
selectively kills Diamondback moth (DBM); A combination of the two pesticides
(Karate and Bt.) and Untreated controls. Parameters included; relat ive
abundance of the three species of aphids; their corresponding damage to
cabbage; the number of mummies per sample; percent parasitism and the
proportions of the primary- and hyper-parasitoids hatched. The parasitoid
complex was constructed from the identified parasitoids.
The results showed aphid counts to be higher in non karate-treated plots than
in the karate-treated ones. More hyperparasitoids notably Alloxysta sp and
Pachyneuron sp. than the only primary parasitoid (Diaeratiella rapae) emerged
from non karate-treated plots. This might suggest that karate might have the
advantage of repelling hyperparasitoids or inhibiting their emergence. Yield
showed some negative correlation with aphid infestations. A combined
treatment gave the best overall yield at both sites.