Chemical composition and insecticidal effect of essential oils from Illicium verum and Eugenia caryophyllus on Callosobruchus maculatus in cowpea

Abstract

The cowpea weevil Callossobruchus maculatus Fabr. (Coleoptera: Chrysomelidae: Bruchinae) is the major pest in stored cowpea, especially in subtropical countries. Thus, the present study aimed to evaluate the insecticidal potential of the essential oils of Illicium verum Hook. F. and Eugenia caryophyllus Spreng on adults of C. maculatus. The components of the essential oils were obtained and identified, the contact toxicity and the repellent and fumigant effect were determined. In the contact and fumigation test the lethal concentrations LC50 and LC95 were determined, the lethal concentrations determined in the contact test were used in the repellency test. For contact and repellency tests, the number of eggs and adults emerged were counted. According to the chemical analysis of the oils, E-anethole (88.85 %) and eugenol (74.31 %) for I. verum and E. caryophyllus, respectively, were the compounds in greater quantity. The values of lethal concentrations LC50 and LC95 in the contact test were estimated at 9.62 and 32.78, 1.27 and 11.95 μL/20 g, respectively, for the oils of I. verum and E. caryophyllus. The essential oil of E. caryophyllus presented higher toxicity for both lethal concentrations, being 5.44 and 2.74 times more toxic than I. verum for LC50 and LC95, respectively. In contact and repellency tests both oils reduced the number of eggs and insects emerged. The LC95 concentration for both oils was repellent to C. maculatus. The essential oils of E. caryophyllus and I. verum presented a potential fumigant effect on C. maculatus with relatively low lethal concentration (LC50) (22.36 and 20.27 μL/L of air for I. verum and E. caryophyllus, respectively), thus being an alternative to synthetic chemical insecticides for the control of stored grain pests.