Apertura mandibular y acarreo de cebos en hormigas cortadoras del género Acromyrmex sp.

Leaf-cutter ants are the main forest pest in the region, causing economic losses in both Eucalyptus and Pinus plantations.

The most efficient way to control them so far is the application of chemical baits, which are transported to the nest. This is why the success of such control depends on the ants lifting the bait.

Under the hypothesis that not all species of Acromyrmex can lift the currently used commercial baits with the same efficiency, we proceeded to evaluate the effect of mandibular opening on the ability of Acromymrex workers to forage on ant baits. For this purpose, two species of Acromyrmex present in the study area with different mandibular openings were compared: Acromyrmex lundii and Acromyrmex heyeri.

Colonies of both species were located at the Facultad de Agronomía in autumn 2022 and were offered Lampo (AI: fipronil) and Dinagro (AI: sulfluramid) baits. Ants collecting the bait were measured for the time taken to recognise the bait, accept it and lift it to the path, head size, mandibular opening and weight of the worker, as well as the length of the lifted pellet.

The results obtained in this study indicate that among the workers that did not carry bait, A. lundii has a greater jaw opening capacity than A. heyeri, however, with regard to head size, A. heyeri is the one with the largest head size, with the majority being between 2.0 mm and 3.0 mm, while for A. lundii it ranges between 1.5 mm and 2 mm. As for the time taken by the ants to lift the bait, only 17% was explained by the variables studied: head width, ant weight and bait length. There are significant differences between the length of the bait and the time it takes to lift the bait for both species. In turn, it is observed that A. lundii workers take longer to travel the 40 cm than A. heyeri workers. Of the two explanatory variables, the one that had the greatest significance and explained the greatest percentage of the variation in the time taken to travel 40 cm was the ant's weight. A. heyeri appears unaffected by bait length or the weight of the ant during transport, allowing it to move faster.

A. lundii achieves larger mandibular openings than A. heyeri and as the commercial baits that exist to date for the control of leaf cutter ants are up to 2 mm, both A. heyeri and A. lundii are capable of lifting the bait because of their mandibular opening capacity, so the failures in the control would not be explained by this physical factor.