Insecticidal Effect of Usnea longissima (Parmeliaceae) Extract against Sitophilus granarius (Coleoptera: Curculionidae)

Two secondary metabolites (diffractaic acid & usnic acid) and extract of a lichen species, Usnea longissima Ach. were tested against adults of Sitophilus granarius (L.) on Petri dishes. After exposure, mortality of the adults was determined at 24th, 48th and 96th h. The results showed that secondary metabolites and extract of U. longissima have an insecticidal effect on adults of Sitophilus granarius (L.) in comparison with controls. The insecticidal effect was influenced by the concentrations of the extracts and the exposure time. Higher concentrations and longer exposure time resulted in maximum toxicity on S. granarius. Treatment with extract and lichen compounds of U. longissima pointed out equal mortality against adults of S. granarius. The mortality rates after 96 h of treatment with the maximum concentration (10 mg mL-1) of U. longissima extract, diffractaic acid and usnic acid were determined as 98.98, 91.91 and 94.94% for S. granarius, respectively. However, there was no mortality in the controls. The mortality rates after 96 h of treatment with the 10 mg mL-1 in concentrations of the extract of U. longissima were established and the highest mortality rate was found against S. granarius with 98.98%.