CONTACT TOXICITY OF ESSENTIAL OIL OF Croton pulegiodorus BAILL ON Sitophilus zeamais MOTSCHULSKY

Abstract

The objective of this work was to evaluate the contact toxicity of essential oil of Croton pulegiodorus Baill on six populations of Sitophilus zeamais Motschulsky. The S. zeamais populations used were from Crixás-GO, Espírito Santo do Pinhal-SP, Juiz de Fora-MG, Picos-PI, Serra Talhada-PE, and Vicentina-MS, Brazil, and present different susceptibility to synthetic insecticides. The essential oil of C. pulegiodorus used was obtained from plants collected in Triunfo-PE, Brazil. The lethal concentrations (LC₅₀ and LC₉₀), toxicity ratio of the essential oil, and the resistance ratio of the populations were estimated. The S. zeamais population from Serra Talhada-PE presented the lowest LC₅₀ (4.21 μL 20 g^-1) and LC₉₀                   (6.67 μL 20 g^-1), and was the reference for susceptibility to the essential oil of C. pulegiodorus. The S. zeamais population from Espírito Santo do Pinhal-SP presented the highest LC₅₀ (6.02 μL 20 g^-1) and LC₉₀                       (10.55 μL 20 g^-1), and was the reference for tolerance to the essential oil of C. pulegiodorus. The toxicity ratio ranged from 1.01 (Picos-PI) to 1.43 (Serra Talhada-PE); and the resistance ratio ranged from 1.13 (Crixás-GO) to 1.43 (Espírito Santo do Pinhal-SP). The essential oil of C. pulegiodorus reduced the emergence of adult S. zemais and showed residual effect, with contact toxicity, after 30 and 60 days of application.