Exploiting Natural Products from African Biodiversity in Pest Management: from Extraction of Plant chemicals to Expression in GMOs

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Exploiting Natural Products from African
Biodiversity in PestManagement from Extraction
of Plant chemicals to Expression in GMOs

• BY
• Joseph M Nguta, PhD

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Introduction

• Natural products have for long provided leads for
  pesticides (especially insecticides)
• Classic examples includeneonicotinoids Spinosad
• Also natural products from the pyrethrum daisy,
  Chrysanthemum ( tanacetum) cinerariifolium
  (Asteraceae) permethrin, cypermethrin and
  deltamethrin

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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.

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Repellents against insect vectors of pathogens

• Natural products in this category include
• Neonicotinoids
• Pyrethroids
• Metofluthrin
• eucamalol from Eucalyptus camaldulensis
  (Myrtaceae)
• Ocimum spp (Lamiaceae)

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Repellents against insect vectors of pathogens

• Gum haggar from Commiphora holtziana
• (Burseraceae)-highly active against ticks and
  mites attacking cattle and camels

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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).

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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)

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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

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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

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Release from GM plants

• By heterologously expressing the
  C-glycosyltransferase 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).

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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)