Repellent potential of agroecological extracts: Exploring their efficacy against the leaf-cutting ant Acromyrmex subterraneus in the laboratory

Abstract

The increasing restrictions on commercial toxic baits for controlling leaf-cutting ants have started a “gold rush” for alternative compounds, with agroecological extracts emerging as a promising option. Here, we tested for the first time the repellent effects of concentrated and diluted ant extracts and cow urine solution on laboratory colonies of Acromyrmex subterraneus (Forel) (Hymenoptera: Formicidae). The agroecological extracts preparation and application followed the information provided by peasants from the Movimento dos Trabalhadores Rurais Sem Terra in Brazil who carry out agroecology. First, we applied the agroecological extracts in the middle segment of the upper path of a foraging trail to determine whether they act as a chemical barrier. All agroecological extracts induced the deviation of the foraging flow from the upper path to the lateral path. However, only the concentrated ant extract reduced the leaf delivery rate. Also, we applied the agroecological extracts directly on the leaf disks and conducted a paired selection test. The proportion of transported leaf disks with concentrated ant extract and cow urine solution was lower than that of control disks. We suggest that the observed repellent efficacy of the concentrated ant extract may stem from its content of chemical compounds belonging to the same chemical group as the alarm pheromones found by other Acromyrmex species. As for the cow urine solution, we attribute its repellent effect to the presence of urea. Our findings highlight a significant repellent potential of the concentrated ant extract and cow urine solution for leaf-cutting ants, which may be applied both on foraging trails and on leaves of cultivated plants.