Abstract:
【Aim】 Plants secondary metabolites are potentially considered as suitable alternatives for chemical pesticides if their extents of impacts were well studied earlier on different groups of pests. This study aims to evaluate the possible impacts of solvent polarity on the insecticidal activity of different plant extracts. 【Methods】 The extraction solvents were selected from a wide range of polarities, n-hexane, ethyl acetate and methanol. The lethal effects of Petroselinum sativum seed extracts as well as Thymus vulgaris and Stachys lavandulifolia shoot extracts on Callosobruchus maculatus adults at 28±2℃, 50%±5% RH and a photoperiod of 16L∶8D were evaluated, and their ovicidal and oviposition deterrence effects were also evaluated. 【Results】 The lowest LC₅₀ value for contact toxicity to C. maculatus adults was associated with the n-hexane extract of T. vulgaris (0.05 g/mL) following with the ethyl acetate and methanol extracts, respectively. The ethyl acetate extract of T. vulgaris had the lowest LT₅₀ value (10.04 h), with the highest relative speed of kill index (42.23%) among all the extracts. All of the extracts at LC₂₀ and LC₅₀ concentrations resulted in 100% ovicidal activity in contact toxicity to C. maculatus adults. In terms of oviposition deterrence, the methanol extract of S. lavandulifolia had the highest deterrence activity (97.54%). 【Conclusion】 Based on the results, it is concluded that T. vulgaris, P. sativum and S. lavandulifolia extracts show significant performances in terms of insecticidal and ovicidal toxicities as well as oviposition deterrence against C. maculatus adults. However, non-polar (n-hexane) extracts of the studied plants show better performances in comparison with other extracts.

Key words: Callosobruchus maculatus, plant-derived insecticides, solvents, crude extract, biological activity