Contamination and mortality of leaf-cutting ant workers by the quinone inside inhibitor fungicide after social interactions.

Leaf-cutting ants of the genera Atta and Acromyrmex (Hymenoptera: Formicidae) are the most important pests in forest and agricultural plantations and livestock. Toxic baits are the main method to manage these insects. The objective was to determine whether the behavior of allogrooming, touch, and self-grooming among Atta sexdens rubropilosa Forel, 1908 (Hymenoptera: Formicidae) workers disperse the fungicide quinone inside inhibitor and whether this product is toxic to them. This fungicide was applied, topically, in groups of workers and the social interactions between them and their mortality with and without the fungicide were evaluated. The interactions and the quinone inside inhibitor fungicide contamination increased with the number of leaf-cutting ant workers per group. Excessive touches, with subsequent allogrooming, and self-grooming among the ant workers dispersed the quinone inside the inhibitor fungicide causing 100% mortality and indicating its toxicity to this insect. The hypothesis that social interactions contaminated ant colony mates and the toxicity of the fungicide quinone inside inhibitor to workers of the leaf-cutting ant A. sexdens rubropilosa was proven.

Herbivory by Atta vollenweideri: Reviewing the significance of grass-cutting ants as a pest of livestock.

The grass-cutting ant Atta vollenweideri is well suited for studies examining the negative effect leaf-cutting ants have on livestock production in South American grasslands because they forage on the same plants as cattle. This study investigated the impact of A. vollenweideri on livestock production in Argentinean rangelands. First, we assessed A. vollenweideri herbivory rates and its economic injury level (EIL). Second, using satellite imagery in a region covering 15,000 ha, we estimated the percentage of this area that surpassed the calculated EIL. Results showed that A. vollenweideri consumed approximately 276 kg of dry plant weight/ha/year, foraging mostly on grasses (70%). Additionally, ants cut 25% of herbs and 5% of trees. In summer and autumn, ants consumed more grasses, while in winter and spring, herbs and trees were also significantly cut. Ants consumed 7% of the forage demand needed to raise a calf according to the management regime applied by farmers. Our calculated EIL (5.85 nests/ha) falls in the range of previous studies. Colonies were absent in 93.6% of the surveyed area, while their density was below the EIL in 6.2% of the area. A. vollenweideri populations surpassed the EIL in only 0.2% of the area, which corresponds to 2.6% of the locations holding colonies. These results question the perception that Atta leaf-cutting ants are a pest of livestock production. Although ants consume a small percentage of cattle's forage demand, evidence that ants and cattle are competing in the few cases in which density surpasses the EIL is arguable. First, grass-cutting ants are capable of consuming herbs and trees in addition to the grasses on which cattle mostly feed. Second, there is no evidence indicating that both are cutting the same plant portions when preferences overlap. Third, evidence suggests that ants are not displaced under high-pressure grazing regimes by cattle. In the countries where A. vollenweideri is present, decision makers have promulgated several acts making its control mandatory. It is time to revisit the pest status of A. vollenweideri and include the use of EIL as a control criterion.

Chemical control of Acromyrmex lundi (Hymenoptera: Formicidae) in anthropic ecosystems.

BACKGROUND: Leaf-cutting ants are pests in agriculture, forests and pasture and, usually, controlled with toxic baits. The management and control of leaf-cutting ants is complex as a consequence of its sociability and behavior. We tested three toxic baits with abamectin, fipronil and sulfluramid to control colonies of Acromyrmex lundi Mayr, 1865 (Hymenoptera: Formicidae), in two seasons: 'Spring 2020' and 'Summer 2020/21', in Argentina. RESULTS: The percentage of effective bait carried in the spring was similar between treatments with 80%, 80% and 90% for those with abamectin, fipronil and sulfluramid. The ant flow of A. lundi decreased after toxic bait applications compared to the control through time in all treatments. This activity was higher in the spring than in the summer. The baits reduced the foraging activity of A. lundi from 5 to 96 days after application (DAA). Abamectin and fipronil baits controlled 50% and 67% of the nests in the spring, and 20% and 43% at 96 DAA in the summer. Sulfluramid was the best treatment, killing 90% of A. lundi nests. CONCLUSION: The baits decrease the foraging activity of A. lundi until 96 DAA, with total or partial death of its colonies varying between treatments. The ant symptoms with the sulfluramid bait appeared faster than with fipronil and may be a result of the low level of carry-over or differences in the chemical quality of the active ingredients. © 2022 Society of Chemical Industry.