Synthetic Carvacrol Derivatives for the Management of Solenopsis Ants: Toxicity, Sublethal Effects, and Horizontal Transfer

Ants belonging to the genus Solenopsis are highly significant invasive pests worldwide. The control of these insects has historically relied on the use of synthetic insecticides, which, unfortunately, has led to a range of ecological repercussions. In light of these challenges and the limited availability of registered products for managing these pests, our study set out to synthesize and assess the insecticidal properties of carvacrol derivatives. The lethal and sublethal effects caused by these derivatives were compared to the essential oil of Lippia gracilis (50.7% carvacrol) and to the base molecule—carvacrol. Carvacryl benzoate was the most toxic derivative to Solenopsis sp., with an LD 50 of 3.20 μg/ mg. This compound was about 2 and 7.6 times more toxic than carvacrol at the doses needed to kill 50 and 90% of populations, respectively. The workers of Solenopsis sp. showed a rapid reduction in survival when exposed to carvacrol (LT 50 = 8.43 h) and carvacryl benzoate (LT 50 = 8.87 h). Insects treated with sublethal doses of the compounds did not show significant effects on self-cleaning, allogrooming and aggregation, with the exception of those treated with L. gracilis essential oil. The oil increased self-cleaning and reduced allogrooming and aggregation. Ants treated with carvacrol and carvacryl benzoate travelled greater distances and had higher movement speeds when compared to the control. These compounds exhibited decreased meanders and angular velocities. When live workers were exposed to dead individuals at the LD 90 of the compounds, carvacryl benzoate was the derivative that most reduced survival due to horizontal transfer. These findings underscore the considerable potential of carvacrol derivatives, specifically carvacryl benzoate, as an alternative approach to managing ants of the Solenopsis genus.