Monarda didyma Hydrolate Affects the Survival and the Behaviour of Drosophila suzukii

Abstract

<i>Drosophila suzukii</i> (Matsumara) is an herbivorous pest whose control in the field with conventional chemical is particularly difficult and has important drawbacks. Here, we investigated the insecticidal properties of hydrolate from <i>Monarda didyma</i>, scarlet beebalm, an aromatic herb in the Lamiaceae family. The identification of volatile organic compounds (VOCs) by CG-MS systems revealed that thymol (38%) and carvacrol (59%) were the most abundant VOCs in the hydrolate. <i>M. didyma</i> hydrolate did not show fumigant toxicity. Conversely, in contact assays, <i>M. didyma</i> hydrolate showed a LC₅₀ of 5.03 µL mL^-1, 48 h after the application on <i>D. suzukii</i> adults. Expression of detoxification genes increased in flies that survived the LC₅₀ application. Furthermore, toxicity persisted for 7 days after the treatment in the survival evaluation. Artificial diet assays with 100 and 1000 µL mL^-1 of <i>M. didyma</i> hydrolate resulted in a significant decrease in total food intake in both male and female <i>D. suzukii</i> adults. In addition, electropenetrography (EPG) showed that the <i>D. suzukii</i> females' feeding behaviour was altered in hydrolate-treated diets. The hydrolate also caused a significant reduction in the number of eggs laid in two different oviposition assays. Overall, our findings provide a new perspective for the improvement of <i>D. suzukii</i> control strategies through <i>M. didyma</i> hydrolate.