Essential oil of Lippia sidoides and its major compound thymol: Toxicity and walking response of populations of Sitophilus zeamais (Coleoptera: Curculionidae)

The maize weevil, Sitophilus zeamais (Motschulsky) (Coleoptera: Curculionidae), is the main pest of stored grains across tropical regions. An alternative strategy to the use of synthetic insecticides for the management of S. zeamais is the development of botanical insecticides based in the essential oils (EOs) from aromatic plants. In the present study, we evaluated the lethal and sublethal effects of the EO of Lippia sidoides (Cham.) and its major compounds (thymol and rho-cymene) on different populations of S. zeamais. For this, we determined toxicity by fumigation of treatments of five populations from different Brazilian regions and assessed the lethal time and walking behavior for the most tolerant and susceptible populations. The lethal concentration required to kill 50% of S. zeamais populations ranged from 35.48 to 118.29 mu L L-1 air for EO of L. sidoides, 65.00-91.23 mu L L-1 air for thymol and 801.24 to 2188,83 mu L L-1 air for rho-cymene. Population from Jacarezinho was the most tolerant to treatments, while population of Rio Branco was the most susceptible one. The survival of S. zeamais populations was significantly affected by treatments and rho-cymene showed the faster action on both Jacarezinho and Rio Branco populations (LT50 = 0.3 h). The walking behavior of maize weevil showed that the EO of L. sidoides and thymol present repellent effect, however, rho-cymene present attractive effect. Therefore, the EO of L. sidoides and its major compound thymol are promising source to develop bioinsecticides for the management of S. zeamais populations with different levels of resistance.