Nest refuse extract deters ant herbivory

Abstract

Leaf-cutting ants (LCA) try to reduce the risk of contamination in their colonies by avoiding contact with their nest refuse (NR), as it can harbor substances harmful to them and their symbiotic fungi. Here, we tested whether an aqueous extract with 10% (vol/vol) of NR of the leaf-cutting ant Atta opaciceps Borgmeier (Hymenoptera: Formicidae, Attini) causes a deterrent effect. We placed leaves of Hibiscus rosa-sinensis L. (Malvaceae) sprayed with NR extract or distilled water (control) in the foraging areas of 12 colonies -eight colonies of A. opaciceps and four of Atta sexdens (L.) -for 60 min, on three consecutive days. The fresh weight of remaining leaf fragments between treatments was compared using linear-mixed effect models. Leaf consumption was significantly lower in the presence of NR extract for 48 h, indicating that the NR odor impregnated in the leaves may have been the responsible factor for the deterrence. Further studies are needed to establish a deterrent extract with a broad spectrum and lasting effect on plants, and to better understand the mechanisms involved in deterrence.

Repellent Effect of Leaf-Cutting Ant Waste Against the Aphid Lipaphis erysimi (Kaltenbach)

“…Similarly, A. opaciceps was chosen because it is easily found in open areas of the hinterland, roadsides, and urbanized areas throughout the Brazilian Northeast, common in Sergipe, forming nest mounds up to 5 m in diameter, with numerous entrances distributed radially as the colony matures [22]. It has underground disposal chambers, but in some cases, colonies dispose of garbage outside the colony [10].…”

“…The hydroalcoholic extracts were prepared at a concentration of 20% vol/vol, adding 80mL of 100% ethyl alcohol, 80mL of distilled water and 40mL of substrate separately for each species, mixed at the time of preparation and twice a day, left to rest at room temperature for 48h, after which they were filtered and stored at room temperature, following the methodology described by Sousa-Souto et al (2022) [10]. The commercial substrate Vitaplan®, composed of Pinus sp.…”

“…Previous studies have reported an increase in the mortality of workers in contact with disposal chambers [14,15]; thus, contact would be avoided by forager workers [7,9]. More recently, Sousa-Souto et al (2022) [10] observed a drastic reduction in the herbivory of Atta sexdens and A. opaciceps in plants treated with liquid extract from NR and pointed to the odor of the material as one of the mechanisms responsible for repellency. At the same time, several substances produced by specific glands in ants have antifungal or bactericidal functions, such as the mandibular and metapleural glands, which are directly related to the hygiene of workers and the colony [16,17].…”

“…Recent studies indicate that the waste substrate produced by leaf-cutting ants (Hymenoptera: Formicidae) (genera Atta and Acromyrmex) has a repellent effect on their own foraging [7][8][9][10]. The waste (here referred to as 'nest refuse' or NR) is composed of the remaining particles of plant material transported by the ants into the nest, the remains of dead ants, and the unconsumed and degraded symbiotic fungus [11].…”

“…Thus, NR can become toxic and is therefore constantly removed from places where the healthy fungus, queen, eggs, and larvae are present. Depending on the ant species, NR is deposited either in the internal chambers of the colony excavated for this purpose or externally in an area close to the colonies [10,13].…”