Long-term quantification of leaf-cutting ant damage in willow forestations in the lower delta of the Parana River, Argentina

Leaf-cutting ants are major pests of Neotropics forest plantations. The lower delta of the Parana River contains the main Argentine Salicaceae production, strongly attacked by Acromyrmex lundii and Acromyrmex ambiguus. Nevertheless, there is no damage quantification in willow plantations attributed to leaf-cutting ant species. In an area without leaf-cutting ant control, we installed 15 blocks with eight willow stakes each: four clones x two treatments; with and without leaf-cutting ant exclusion. We used two traditional (Americano, Nigra 4) and two new (Geminis, Yaguarete) commercial clones. During 2014-2018, we measured the damaged foliage, height and diameter of each tree. Foliage was damaged intensely during the first 2 years. After 1537 days, the loss in height and diameter was greater in Americano (70%), followed by Geminis (50%-60%), Yaguarete (40%-50%) and Nigra 4 (45%-40%). Stake survival with exclusion was greater (>80%) than stakes without exclusion (<50%). Total loss of wood volume was 93% for Americano, followed by Geminis (77%), Yaguarete (66%) and Nigra 4 (51%). Although the new clones were heavily attacked, they produced two to three times more wood volume than Americano; replacing Americano with the new clones would help to reduce leaf-cutting ants impact on plantations and pesticides released into the environment.