Biological activities and chemical composition of Mentha piperita and Syzygium aromaticum essential oil fractions against cowpea weevil, Callosobruchus maculatus (Fabricius) (Coleoptera: Bruchidae)

Callosobruchus maculatus (Fabricius) is one of the major, common, pests of stored grains as it causes quantitative and qualitative losses in legume crops. This research sought to find the most active fraction in Mentha piperita and Syzygium aromaticum essential oils, to evaluate bioactivity of those crude essential oils and active fractions against C. maculatus, and to identify the compounds contained in the active fraction. The essential oils were fractionated using three solvents, namely n-hexane, ethyl acetate, and methanol. The n-hexane fraction was identified as the active fraction, causing mortality, oviposition deterrence, and ovicidal effects. In fumigation chambers, LD95 values of M. piperita (Mnf) and S. aromaticum n-hexane fractions (Snf) were 0.045 ml/l and 0.057 ml/l respectively. ED50 values for oviposition deterrence were 0.016 ml/l for Mnf and 0.022 ml/l for Snf. ED50 value of ovicidal effects for Mnf- and Snf-treated eggs were 0.014 ml/l for both fractions. GC-MS analysis showed 8 dominant compounds in Mnf and 5 dominant compounds in Snf. Overall it is concluded that Mnf and Snf oils have effective biological activities against stored pest C. maculatus and have potential to be considered as alternatives to synthetic insecticides.