Repellent activity and fumigant toxicity of a few plant oils against the adult rice weevil Sitophilus oryzae Linnaeus 1763 (Coleoptera: Curculionidae)
Manickkam Jayakumar, Subramanian Arivoli, Rajasingh Raveen and Samuel Tennyson
Insect pests cause damage to stored grains and processed products by reducing their dry weight and nutritional value. The control of rice weevil infestations has been primarily through the use of fumigants and residual chemical insecticides to augment the more obvious approach of hygiene. Treatment of rice with synthetic insecticides is not recommended because of direct and indirect health hazards to humans. Recognition of such detrimental effects of synthetic insecticides has prompted the development of new alternatives as less obtrusive management strategies that must be ecologically safer with no residual and noxious effects on non-target animals. Plant based formulations are chiefly biodegradable and are recognized as better sustainable and eco-friendly alternatives of synthetic pesticides in food security as their activity may be due to synergistic effects of different active principles leading to different mode of action during their pesticidal action. Therefore, in the present study, the repellent activity and fumigant toxicity of plant oils viz., Aniseed, Camphor, Citronella, Eucalyptus, Geranium, Lavender, Lemon, Rosemary, Vetiver and Wintergreen were tested at concentrations of 10 and 50µL against the adults of Sitophilus oryzae in the laboratory. Results revealed varying degree of repellency by plant oils on the adults of Sitophilus oryzae. Among the plant oils tested, maximum repellency expressed as Excess Proportion Index (EPI) was recorded in camphor. The order of the repellency of plant oils at 10µL on 6 hours of exposure with EPI were Camphor (-0.90) Wintergreen (-0.88) Lavender (-0.70) Citronella (-0.70) Rosemary (-0.67) Vetiver (-0.62) Lemon (-0.57) Eucalyptus (-0.55) Geranium (-0.44) Aniseed (-0.04) and at 50µL it was Camphor (-1.0) > Wintergreen (-0.89) Citronella (-0.89) Lemon (-0.89) Lavender (-0.71) Vetiver (-0.69) Geranium (-0.65) Rosemary (-0.57) Eucalyptus (-0.52) Aniseed (-0.50). For fumigant toxicity (expressed in terms of adult mortality), the selected plant oils were tested at 10 and 50µL concentrations for 24, 48 and 72 hours, and Lemon oil exhibited the highest activity and their respective LD50 values were 58.86, 44.90 and 40.38µL. Results of this study indicate that plant oils might be useful for managing coleopterous insects in storage especially Sitophilus oryzae on rice. Yet, further scrutiny is required to use plant oils as one of the component in IPM programmes which may reduce the application of synthetic chemicals.
Manickkam Jayakumar, Subramanian Arivoli, Rajasingh Raveen, Samuel Tennyson. Repellent activity and fumigant toxicity of a few plant oils against the adult rice weevil Sitophilus oryzae Linnaeus 1763 (Coleoptera: Curculionidae). J Entomol Zool Stud 2017;5(2):324-335.