Exploiting Natural Products from
African Biodiversity in Pest
Management: from Extraction of
Plant chemicals to Expression in
GMOs
BY
Joseph M Nguta, PhD
Introduction
• Natural products have for long provided leads
for pesticides (especially insecticides)
• Classic examples include:neonicotinoids;
Spinosad
• Also natural products from the pyrethrum
daisy,
Chrysanthemum
(=
tanacetum)
cinerariifolium (Asteraceae): permethrin,
cypermethrin and deltamethrin
Introduction
• By exploiting African biodiversity, compounds
can be identified for exploitation locally and
internationally in pest management
• Natural products with biopesticidal potential
will be discussed.
Repellents against insect vectors of
pathogens
•
•
•
•
•
Natural products in this category include:
Neonicotinoids
Pyrethroids
Metofluthrin
eucamalol from Eucalyptus camaldulensis
(Myrtaceae)
• Ocimum spp (Lamiaceae)
Repellents against insect vectors of
pathogens
• Gum haggar from Commiphora holtziana
• (Burseraceae)-highly active against ticks and
mites attacking cattle and camels
Antifeedants against crop pests
• Natural products with potential to yield
antifeedants against crops include:
• Ajuga spp. (Lamiaceae), particularly A. remota,
yielding ajugarin 1
• The tree Warburgia ugandensis (Canellaceae),
yielding ugandensidial
• However, although these could be used locally
and also form the basis of exports to the north,
such products have not yet been exploited.
(Pickett et al. 1987).
Direct production of crop protection
agents by companion crops
• Natural products in this category include:
• Forage legumes in the genus Desmodium
(Fabaceae), which also dramatically controls
the African parasitic witch weeds in the genus
Striga (Orobanchaceae), particularly S.
hermonthica
• Each companion crop is also used as forage for
cattle or dairy goats
(Khan et al. 1997; Hassanali et al. 2008)
Release from GM plants
• By identifying the chemistry of the companion
crops that is responsible for repelling pests
and attracting beneficial insects, new targets
for genetic modification, for example,
increasing production of 4,8,12-trimethyl(E,E)-trideca-1,3,7,11-tetraene which both
repels pests and attracts parasitic wasps have
been identified
Release from GM plants
• Currently, research is ongoing on elicitors from
the eggs of maize stem borers to identify elicitors
that can have dramatic effects on the defense
chemistry of African grasses (Bruce et al. 2010).
• The compounds from Desmodium uncinatum that
interfere with the development of the parasitic
weeds Striga spp. comprise C-glycosylated
flavonones and recently, the mechanism by which
these compounds are biosynthesised (Hamilton
et al. 2009) has been elucidated
Release from GM plants
• By heterologously expressing the Cglycosyltransferase enzymes involved into
edible beans, it is possible to create
companion intercrop plants useful as human
food but embodying the novel trait for
controlling Striga spp.
(Pickett et al. 2010; Khan et al. 2010).
Acknowledgements
• CPD secretariat, PHPT (For facilitating my
participation)
• Dr. Mbaria (For his useful criticism)
• University of Nairobi (for giving me an
opportunity to serve in this World Class
University)
• Dr. S.G.Kiama (for provision of visionary
leadership in natural product research)