Insights on biorational potential of Ocimum gratissimum essential oil and its binary combination with monoterpene phenol for control of rice weevil (Sitophilus oryzae) and aflatoxigenic fungi.

Food grain storage is a difficult task due to insect infestation and subsequent mycotoxin contaminations which adversely affects the nutritional quality of grains and leading to economic loss. Current research focuses on contact and fumigant toxicity effects of essential oils (EO) and aroma compounds against Sitophilus oryzae and growth inhibition of aflatoxigenic fungi. The EO of Ocimum gratissimum comprised of thymol (46.8%), γ-terpinene (14.04%) along with o-cymene (11.76%). Also, Cymbopogon flexuosus rich in citral (76.3%) and geraniol (84.6%) and Cymbopogon nardus having geraniol (49.24%) and geranyl acetate (20.9%) were all evaluated using a dose of 25 μL (Conc∼833.3 μL/L air) against S. oryzae . All the compounds showed significant mortality (>95%) at 24 hours of exposure. The insecticidal property of O. gratissimum oil chemotype showed a strong contact and fumigant toxicity against S. oryzae at a highest dose of 25 μL (Conc∼833.3 μL/L air) within 24 hours. It has been further evaluated on three aflatoxigenic fungal strains which showed reduction in growth and aflatoxin content (Aflatoxin B and G), which was markedly reduced upon the treatment. The binary mixture interaction of O. gratissimum oil with monoterpene phenol (carvacrol) was assessed and the specific binary mixture of 80:20 ratio (having additive property) acts as a contact insecticide with 100% mortality. Hence, essential oil of less explored Ocimum species ( O. gratissimum ) and its binary mixture could be deployed as potential biorational for control of rice weevil ( Sitophilus oryzae ) and aflatoxigenic Aspergillus spp. • Essential oil of Ocimum gratissimum chemotype rich in thymol exhibits strong contact and fumigant toxicity against Sitophilus oryzae. • The binary mixture O. gratissimum oil with carvacrol at 80:20 ratio revealed additive property with improved insecticidal property. • O. gratissimum oil entails a significant deformity on setae, scales and pits of rice weevil elytra. • Differential inhibition of aflatoxin types noticed with aflatoxigenic fungi with O. gratissimum treatment.