Maize occupies an important place in the resolution of food insecurity problems in the
sub-Saharan region of Africa. However due to poor post-harvest technologies, more
than 35% of annual crop yield is often lost during storage as a consequence of insect
attack. While chemical pesticides constitute an efficient tool for reducing these losses,
current excessive usage runs the risk of modifying the quality and safety of foods
produced from these grains. The use of essential oils of plant origin for grain storage
has been advocated as a non invasive method with limited or no effect on the quality
and safety of the grains or their products. This study was carried out as an evidence of
bioactivity of two essential oils of
Clausena anisata
(Willd.) Hook and
Plectranthus
glandulosus
Hook F. against adults of
Tribolium castaneum
Herbst and
Sitophilus
zeamais
Motschulsky, which are two important stored product insect pests in
Northern Cameroon. Because of the low persistence of the insecticidal activities of
these plants, their essential oils to achieve a complete protection of the stored products
must be applied at frequent delays. The present investigation focuses on the
occurrence of residues of these oils on treated maize grain and flour. The doses of
crude essential oils used to treat adults of
S. zeamais and
T. castaneum in a contact
and inhalation process were their LD
99s. After the evaluation of their insecticidal
activity the persistence of each essential oil was observed every 2 days till 14 days.
After the disappearance of their insecticidal activities, essential oil was re-extracted
and their residual compounds were identified from treated grain and flour. The major
compounds of
C. anisata are, estragole, α-humulene, germacrene D and (E)-nerolidol.
In
P. glandulosus they are: fenchone, α-terpinolene and piperitenone oxide. After 14
days, only 64.24% of compounds of
C. anisata were recovered on treated flour and
55.16% on grains. Concerning
P. glandulosus, 48.94% was recovered on grains and
61.23% on flour.