Toxicity and repellency of<i>Hoslundia</i><i>opposita</i>Vahl (Lamiaceae) leaves' essential oil against rust-red flour beetle,<i>Tribolium</i><i>castaneum</i>Herbst (Coleoptera: Tenebrionidae)

Abstract

The insecticidal properties of Hoslundia opposita Vahl (Lamiaceae) leaves' essential oil (EO) against Tribolium castaneum were investigated using contact toxicity and repellency bioassays. Mortality progressed with exposure period and ranged from 61.13% observed at 24 h after treatment (HAT) to 88.86% at 168 HAT. The LT50 (lethal time for 50% of treated adults) of H. opposita EO against T. castaneum was 10.42 h. Application of EO at 20-30 μL/30 cm(2) caused significantly (P < 0.05) higher percentage repellency than what was observed in control, 10 and 15 μL/30 cm(2) at 1 and 3 HAT, with significant repellency at 24 HAT regardless of dosage. Repellency class increased with EO dosage, with class V observed at 30 μL/30 cm(2), regardless of exposure duration. The RD50 (repellency dose for 50% of treated adults) of 15.88 and 13.37 μL/30 cm(2) for 1 and 2 HAT, respectively, was significantly higher than 0.09 μL/30 cm(2) at 24 HAT.