Insecticidal Activity of Lichens against the Maize Weevil, Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae)

Extracts of Letharia vulpina (L.) Hue and Peltigera rufescens (Weiss) Humb. lichen species and two major lichen compounds (diffractaic and usnic acids), isolated from Usnea longissima Ach., were tested against adults of the maize weevil, Sitophilus zeamais Motschulsky under laboratory conditions at various concentrations (2.5, 5, 10, 20 mg.ml-1 for extracts and 1.25, 2.5, 5, 10 mg.ml-1 for major compounds) and at 24, 48, 72, and 96 h period. Results showed that both the extracts and the secondary metabolites of U. longissima had significant insecticidal effects on adults of S. zeamais. Mortality rate was the highest at 96 h period at the treatment of maximum concentration of extracts (20 mg.ml -1) and compounds (10 mg.ml-1). The mortality rates attained 96.97, 95.96, 96.97 and 76.77% for L. vulpine, P. rufescens, diffractaic and usnic acids, respectively. No mortality was found in the control. The present results suggest that the lichen extracts and the secondary metabolites can provide a good potential for the control of S. zeamais adults.