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Full Length
Research Paper
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Insecticidal potency of Hyptis spicigera preparations
against Sitophilus zeamais (l.) and Tribolium castaneum
(herbst) on stored maize grains
Othira J.
O.1*, Onek L.
A.1,
Deng L.
A.2, Omolo E.
O.3
1Deptartment
of Biochemistry and Molecular Biology,
Egerton
University, P. O. Box 536 - 20115, Egerton, Kenya.
2Department
of Biological Sciences,
Egerton
University, P. O. Box 536 - 20115, Egerton, Kenya.
3Department
of Crops, Horticulture and Soils,
Egerton
University, P. O. Box 536 - 20115, Egerton, Kenya.
*Corresponding author. E-mail:
othirajack@hotmail.com
.
Fax:
+25405162442.
Accepted 3 February, 2009
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Abstract |
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Food situation has remained insecure and unpredictable in
sub-Saharan Africa, leading to high levels of cyclic famine
and poverty. This has been exacerbated by perennial pest
problems, which cause substantial post-harvest food grain
losses. It is against this background that this study was
designed to investigate the use of Hyptis spicigera
preparations for pest control and hence generate effective
biological control options compatible with the prevailing
farmers’ circumstances. Laboratory and on-farm studies
were conducted in order to assess
the insecticidal potency of H.
spicigera
extracts
on maize weevils, Sitophilus zeamais
Motschulsky
(Coleoptera: Curculionidae)
and red flour beetle (Tribolium castaneum Herbst
(Coleoptera: Tenebrionidae).
Fumigant toxicity was assessed at four rates (0, 2, 4, 6, 8,
10 μl/l air) in space
fumigation whereas repellence was evaluated in choice
bioassay system at five rates (0, 0.2, 0.4, 0.6, 0.8 and
1.0% w/w). Contact toxicity was evaluated by the perforated
jar method using dry powder, fresh leaves and oils while
antifeedant activity was studied by the flour disk method.
The results established that both whole plant parts and
steam-distilled essential oil extracts possess strong insect
repellent activity at reasonably low doses.
Following exposure of newly emerged adult insects to 12 h of
fumigation using essential oils at a dose of 25 μl/vial, 70%
mortality was recorded for H. spicigera and 0% in the
control. Whole plant powder had high potency compared
to polar extracts which were not significantly efficacious
to the insects. Hexane extract
also showed the highest feeding deterrence activity compared
to either ethyl acetate or water extracts. Hyptis oil
extract on maize was also the most effective treatment at
reducing insect infestation and seed damage compared to
other treatments in the field.
Whole plant extracts and essential oils described could be
useful for managing field populations of S. zeamais
and T. castaneum.
Therefore, this study introduces an innovative
approach to the use of traditional plant-based pesticides
for grain protection in Kenya.
Key words:
Hyptis spicigera, bioactivity, antifeedant, toxicity,
repellancy, stored-product insects. |
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