Chemical composition, toxicity and growth inhibitory activities of essential oils of three Achillea species and their nano-emulsions against Tribolium castaneum (Herbst)

Essential oils of Achillea biebersteinii , A. santolina and A. mellifolium were obtained by hydrodistillation, then analyzed using gas chromatography (GC) and GC/mass spectrometry (MS). The obtained oils showed considerable toxic and growth inhibitory activities against the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae). The time of exposure, the technique used and the stage treated, all were activity-determinant factors, where A. biebersteinii oil showed the strongest insecticidal activity and the adult stage was more susceptible than larvae. Using topical application, LC 50 values of A. biebersteinii , A. santolina and A. mellifolium oils after 96 h of exposure of larvae were 30.3, 47.8 and 62.3 μg/mg insect, respectively. In this case, LC 50s against adults were ranged between 21.8 and 50.7 μg/mg insects. Using treated filter papers, the LC 50 values after 96 h of exposure against larvae were ranged between 124.9 and 212.0 μL/cm 2 , while against adults were ranged between 113.0 and 196.8 μL/cm 2 . In the fumigant bioassay, LC 50s after 96 h of exposure against larvae were between 41.7 and 93.2 μL/L air, while against adults were between 36.1 and 80.6 μL/L air. When prepared as nano-emulsions and tested as fumigants, toxicity of oils was increased dramatically, where LC 50 values after 96 h of exposure against larvae and adults were ranged between 11.0 and 27.5 μL/L air and 8.8 and 21.3 μL/L air, respectively. When exposed as 2nd instar larvae to sub-lethal doses-treated grains, the developmental course, life span and F 1 progeny of T. castaneum were significantly affected, where the oil of A. santolina showed the strongest activity. All of these developmental disruptions led to a great reduction in the number of adults that undergo successful emergence.