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Secondary metabolites which make the major contribution to specific odors and flavors of
plants play a critical role when dealing as repellents against insects in storage pest management.
Thus, identification of those secondary metabolites that have repulsive effect on insect pest
behaviors could greatly facilitate the development of green pesticides while ensuring ecological
sustainability. Hence, the present phytocentric research study provides the first investigation
on volatile profile, chemical composition and repellent potential of the leaves of R. graveolens
(Aruda) against the maize weevil, Sitophilus zeamais (Motschulsky) infestations. The volatile
organic compound (VOC) profile of fresh leaves of R. graveolens was analyzed with headspace
solid-phase microextraction coupled with gas chromatography and mass spectrometry (HSSPME/GC-MS). Qualitative phytochemical screening of 11 phytoconstituents (alkaloids,
saponins, flavonoids, tannins, steroids, terpenoids, anthraquinones, glycosides, phlobatannins,
coumarins and phenols) for four leaf extracts (aqueous, n-hexane, ethyl acetate and methanol)
was also performed following the standard procedures. In addition, contact and fumigant
repellent properties of R. graveolens were also evaluated. A total of 14 compounds representing
99.95% of the total quantum of volatiles were detected in R. graveolens leaves consisting
mainly of 2-ketones (93.32%), sesquiterpenoids (1.48%), aliphatic acids and esters (1.29%): 2-
Nonanone (25.71%) and 2-Undecanone (55.51%) were the major volatile compounds followed
by 2-Decanone (5.60%), 5, 6-diethenyl-1-methyl-cyclohexene (3.76%), 2-Dodecanone
(2.74%) and 2-Tridecanone (2.98%). Phytochemical results revealed the absence of
phlobatannins and the presence of alkaloids, glycosides and coumarins in each leaf extract.
Aqueous leaf extract exhibited the presence for majority of phytoconstituents while hexane
demonstrating the least presence. The data on contact and fumigation repellency against S.
zeamais indicated strong maize grain protection activities at the highest dosage accounting for
97% and 96% respectively. The present study provides the evidence that R. graveolens leaves
contain agriculturally important bioactive secondary plant metabolites, thus justifying the use
of plant species with respect to its significant repellent role against S. zeamais populations in
post-harvest storage pest management programs.
