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Essential oil of Ocimum
grattissimum (Labiatae) as Sitophilus zeamais (Coleoptera:
Curculionidae) protectant
E. F. Asawalam1,2*, S. O. Emosairue2
and A. Hassanali1
1Behavioural
and Chemical Ecology Department, International Centre of
Insect Physiology and Ecology P. O. Box 30772-00100 Nairobi,
Kenya.
2Department
of Plant Health Management, Michael Okpara University of
Agriculture, Umudike P. M. B. 7267 Umuahia, Abia state
Nigeria.
*Corresponding author. E-mail: elechiasw@yahoo.com,
easawalam@icipe.org.
Tel: +2348039695157.
Accepted
27 August, 2008 |
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Ocimum
grattissimum
L. (Labiatae) leaves are widely eaten as a vegetable in
Nigeria, and in the eastern parts, are traditionally used in
post-harvest protection and relieving stomach aches. The
effect of the essential oil of O. grattissimum leaves
on Sitophilus zeamais (Motschulsky) (Coleoptera:
Curculionidae) was assessed for repellency, mortality,
progeny emergence and maize damage in the laboratory.
The oil was found to be moderately
repellent to the maize weevil and induced high mortality in
the weevils. In addition, grains treated with the
essential oil showed significant reduction in the number of
progeny derived from surviving S. zeamais. There was
no observable feeding damage on grains treated with the
highest dosage of the essential oil extract. Gas
chromatography-linked mass spectrometry (GC-MS) and GC
co-injections with authentic samples showed the presence of
the following major constituents: thymol (32.7%), paracymene
(25.4%), γ-terpinene (10.8%), β-selinene (4.5%),
phellandrene (3.9%) and β-myrcene (3.1%). The results
provide a scientific rationale for the use of the plant in
post-harvest protection.
Key
words:
Ocimum grattissimum, essential oil, Sitophilus
zeamais, maize, repellency. |
