Do Workers from Subspecies Acromyrmex subterraneus Prepare Leaves and Toxic Baits in Similar Ways for Their Fungus Garden?

Toxic baits are the most efficient method to control leaf-cutter ants in eucalyptus forests for paper and cellulose production. For the proper use of these baits, insecticide compounds must reach workers and contaminate them. Thus, understanding how these baits are processed inside the nests is vital for a successful control, especially when it comes to genus Acromyrmex. Lack of information on toxic baits and on contamination of Acromyrmex workers raises the question: do workers from subspecies Acromyrmex subterraneus (Forel) prepare leaves and toxic baits in similar ways for their fungus garden? To answer it, this study described and analyzed the behavioral repertoire executed by A. subterraneus workers during the preparation of leaf disks and baits and their incorporation into the fungus garden. Results show that the act of licking the substrate was the most frequently executed behavior, regardless of subspecies or size categories. Moreover, additional behaviors have been observed when workers processed the baits, such as licking and scraping their jaws on the surface of the bait pellet, as well as licking and biting fragments of bait pellets, moistening them. Thus, it is concluded that the preparation of baits is different from that of leaves; baits are more processed and can therefore contribute to contaminating workers via insecticides.

Contamination Route of Leaf-Cutting Worker Ants Analyzed Through a Fat-Soluble Tracer Dye in Toxic Bait.

Our study seeks to discover contamination routes of leaf-cutting worker ants during chemical control by formicide baits. To do so, toxic baits containing fat-soluble tracer dye were provided to colonies of three subspecies of Acromyrmex under laboratory conditions, in order to assess the proportion of dyed workers by size category, as well as dyed internal morphological structures. Results showed that nearly 50% of the workers come into contact with the active ingredient, since the internal structures of their bodies are dyed by the fat-soluble tracer dye within the first 24 h from contact with the toxic bait. In addition, the three subspecies of leaf-cutting ants present a similarity as to the contamination of their workers, probably due to their specialized behavior performed during the growth of the fungus garden with the baits. We conclude that the workers' pattern of behavior during fungus garden growth was the main means for dispersion of a fat-soluble substance among approximately half of the nest mates in our experiments, serving as a model for further studies on contamination of worker ants with insecticides.