Insecticidal effects of Thuja occidentalis (Cupressaceae) essential oil on Callosobruchus maculatus [Coleoptera: Bruchidae]

Abstract

Analysis of Thuja occidentalis L. essential oil used for insect fumigation by phase gas chromatography revealed the presence of 22 compounds including α-thujone (49.64%), fenchone (14.06%), and β-thujone (8.98%). Fumigation of adult bruchids with the oil alone resulted in lethal doses (LD50) of 1.1, 0.7, 0.5 and 0.2 μL/insect after 3, 6, 9 and 12 h, respectively. When insects were treated with aromatized powder, significant differences were also found between treatments and control. Application of 100 mg of powder aromatized at 3 μL essential oil g–1 on bruchid pairs lead to 95% mortality of females and 100% of males with 0% of mortality in the control after 6 h exposure. Five days after their deposit, egg hatching was 1.2% (treated with kaolin powder aromatized with T. occidentalis essential oil), 41% (with kaolin alone) and 44% of eggs (control without kaolin). In the same experiment, adult emergence of 80% (in treatments with kaolin alone), 100% in control (without kaolin) and 0% (with kaolin aromatized with T. occidentalis essential oil) were recorded 30 d after treatment. Germination of cowpea seeds was not significantly affected by the treatments. Five days after sowing, germination was 88, 97 and 97%, respectively, when cowpea grains were treated and exposed, treated and unexposed, untreated and unexposed, respectively, while those untreated and exposed had 15% germination. Key words: Thuja occidentalis, Callosobruchus maculatus, essential oil, kaolin, fumigation, ethnobotany.