Nanoformulation prototype of the essential oil of Lippia sidoides and thymol to population management of Sitophilus zeamais (Coleoptera: Curculionidae)

Abstract

Sitophilus zeamais is a pest of global significance and it is difficult to control due to the high indices of resistance to insecticides showed by the populations. As an alternative to the management of S. zeamais populations, in the present study, we evaluated the toxicity of essential oil (EO) of Lippia sidoides, its major compound (thymol − 68.5%) and prototypes of nanoformulations (NF) (18%) based on these compounds on S. zeamais populations (N=5) from different regions of Brazil. Toxicity bioassays were performed to determine lethal and chronic toxicity doses and times to test the efficiency of prototypes in the treatment of stored grains. Additionally, we study the efficiency and stability of stored NFs. The lethal doses of EO of L. sidoides and thymol required to kill 50% of S. zeamais populations ranged from 7.1 to 19.9μg/mg−1 and 17.1 to 25.7μg/mg−1, respectively. The populations of Jacarezinho-PR and Maracaju-MS were, respectively, the most tolerant and susceptible to the EO of L. sidoides. EO of L. sidoides, thymol and its NFs acted fast on the populations of S. zeamais. Increasing of NF concentrations led to reduced grain consumption and total population mortality. NFs stored for up to seven months maintained high mortalities on S. zeamais. This work indicates that the prototypes of NFs based on the EO of L. sidoides and its major compound are promising for the management of S. zeamais populations.