Essential oils obtained from different plants showed several types of pesticide properties; some of
them may be considered alternatives to insecticides for pest control. The main purpose of this research was
to detect the chemical composition of the essential oil derived from the fruits of Litsea cubeba (Lauraceae).
In addition, to evaluate the contact and fumigant toxicity and repellent activities of the essential oil and two
main active ingredients against the adults of two stored grain insect pests; riceweevil, Sitophilus oryzae (L.)
(Coleoptera: Curculionidae) and the red flour beetle, Tribolium castaneum (Herbst.) (Coleoptera: Tenebrionidae)
in the laboratory. Twenty-one components were identified in the essential oil with gas chromatography-mass
spectrometry (GC-MS). The main constituents included E-citral (geranial) (28.49%), Z-citral (neral) (21.57%) and
D-limonene (18.82%) followed by Citronella (3.20%), -pinene (2.85%), Terpinol-4-ol (2.46%), -Thujene (2.34%)
and Geraniol (2.25%). Citral (Z/E-citral) and D-limonene separated as main components from the essential oil.
Results from the three compounds; the essential oil, citral and D-limonene showed strong contact toxicity
against S. oryzae with LD50 7.51, 7.75 and 29.57 μg/l, while fumigation had higher toxicity on the same insects
4.44, 4.89 and 16.68 μg/l, respectively. In the case of the adults of T. castaneum, those were more resistant to
the essential oils and its main active compounds. The contact toxicity of essential oils, citral and D-limonene
against T. castaneum presented LD50 values 253.66, 349.47 and 3803.20 μg/l, while the fumigation toxicity
recorded 204.34, 296.64 and 592.08 μg/l, respectively. Otherwise, the essential oils, citral and D-limonene were
strong repellents against S. oryzae at 60 nL cm2, being 81.83 and 53.30%, respectively after two and four hours
post-treatment. Whereas, the repellency percentages for T. castaneum were 85.76 and 82.33%, respectively, at
the same conditions mentioned before. At the same concentrations, the essential oil had more repellent effect
on T. castaneum than S. oryzae. Thus, the essential oils of L. cubeba might be potential to be developed as a
natural contact and fumigant insecticides or repellents for control of the two insect species under study. |
