Comparative study of individual and Co-application of pyrolysis products of Leucaena Leucocephala tree wastes as natural resources to control the rice weevil Sitophilus oryzae (L.) (Coleoptera: Curculionidae)

Abstract

In this study, the insecticidal activity of individual and co-applications of bio-oil and biochar produced from the residues of the Leucaena Leucocephala(Lamark) deWit (Fabales: Fabaceae) tree by pyrolysis was evaluated against the rice weevil, Sitophilus oryzae. Bio-oil exhibited high insecticidal activity, of 93% mortality at 30% after 7 days, while biochar did not exhibit insecticidal activity, mortality was 32.5% at 3 g kg-1 after 7 days of exposure. An enhancement was recorded for the co-application of 5% of bio-oil at different concentrations of the biochar, and the highest synergistic effect was obtained for 5% of bio-oil + 0.5 g kg-1 of biochar (co-toxicity factor = 30.11-fold). The co-application was re-investigated regarding the mortality and wheat germination percentage after different storage periods, and the results showed no significant changes in the mortality up to 30 days but significantly decreased after 45 days, while the germination percentage was not significantly affected up to 45 days of storage. The gas chromatography-mass spectrometry revealed the prevalence of phenolic compounds and organic acids in approximately 68.19% of the total components in the bio-oil, and the pH was recorded to be highly acidic (pH = 1.5). Additionally, many functional groups were observed on the biochar surface by FTIR, which may have interacted with the chemical components of bio-oil to induce the enhancement action. This study provides information regarding the utilization of the pyrolysis products of lignocellulosic wastes as natural resources to control S. oryzae and protect stored wheat from infestation for up to 30 days.