Dispersant Agents of Essential Oil for Stored Grain Pest Control

The control of insect pests in stored grains carried out through insecticides that may select resistant populations and generate environmental risks. Secondary plant compounds are alternatives to control insect pests. However, the high volatility has been an obstacle in their practical use. This study develops natural dispersants for the application of Mentha piperit a essential oil for the control of Sitophilus zeamais (Motschulsky) (Coleoptera: Curculionidae). Two types of dispersants were tested: a gypsum-based dispersant prepared with a mixture of gypsum and water molded in aluminum, and a sachet dispersant composed of polyester sachets. The efficiency of the dispersants was assessed by contact, fumigation and repellency tests. For that, unsexed S. zeamais up to 15 days old were used and evaluated after 48 hours of experiment assembly. The persistence effects of the essential oil in dispersants were also evaluated. The fumigation test with essential oil in the sachet and gypsum dispersants generated, respectively, LC ₅₀ values of 23.78 and 34.32 and LC ₉₉ values of 54.27 and 79.28 µL. For the contact test, the sachet dispersant presented sublethal and lethal concentrations of LC ₅₀ 25.84 and LC ₉₉ 48.40 µL, respectively. However, only the 26 µL concentration was repellent for both dispersants. The repellent and fumigant effects of the sachet lasted for 15 and 24 days, while these effects in gypsum dispersants lasted 21 and 30 days, respectively. Both dispersants were considered promising as they persistently retained and released the compounds present in the essential oil, enhancing the fumigant and repellent effect against S. zeamais .