Leaf-cutting ants’ critical and voluntary thermal limits show complex responses to size, heating rates, hydration level, and humidity

Thermal variation has complex effects on organisms and they respond to these effects through combined behavioral and physiological mechanisms. However, it is less clear how these traits combine in response to changes in body condition (e.g., size, hydration) and environmental factors that surround the heating process (e.g., relative humidity, start temperatures, heating rates). We tested whether these body conditions and environmental factors influence sequentially measured Voluntary Thermal Maxima (VTmax) and Critical Thermal Maxima, (CTmax) in leaf-cutting ants (Atta sexdens rubropilosa, Forel, 1908). VTmax and CTmax reacted differently to changes in body size and relative humidity, but exhibited similar responses to hydration level, start temperature, and heating rate. Strikingly, the VTmax of average-sized workers was closer to their CTmax than the VTmax of their smaller and bigger sisters, suggesting foragers maintain normal behavior at higher temperatures than sister ants that usually perform tasks within the colony. Previous experiments based on hot plate designs might overestimate ants’ CTmax. VTmax and CTmax may respond concomitantly or not to temperature rises, depending on body condition and environmental factors.

Carbon dioxide levels in initial nests of the leaf-cutting ant Atta sexdens (Hymenoptera: Formicidae)

Claustral foundation of nests by Atta sexdens Forel (Hymenoptera: Formicidae) involves great effort by its queens, solely responsible for the cultivation of the fungus and care for her offspring at this stage. The minimum workers, after 4 months, open access to the external environment to foraging plants to cultivate the symbiotic fungus, which decomposes the plant fragments and produces gongilidea nodules as food for the individuals in the colony. Colony gas exchange and decomposition of organic matter in underground ant nests generate carbon dioxide (CO2) emitted into the atmosphere. We described the carbon dioxide concentration in colonies in the field. The objective was to evaluate the carbon dioxide concentration in initial A. sexdens colonies, in the field, and their development. The CO2 level was also measured in 4-month-old colonies in the field, using an open respirometric system fitted with an atmospheric air inlet. The CO2 level of the respirometric container was read by introducing a tube into the nest inlet hole and the air sucked by a peristaltic pump into the CO2 meter box. The CO2 concentration in the initial colony was also measured after 4 months of age, when the offspring production (number of eggs, larvae, pupae and adult workers) stabilized. Ten perforations (15 cm deep) was carried out in the adjacent soil, without a nest of ants nearby, to determine the concentration of CO2. The composition of the nests in the field was evaluated after excavating them using a gardening shovel and they were stored in 250 ml pots with 1 cm of moistened plaster at the bottom. The CO2 concentration was higher in field nest than in adjacent soil. The concentration of carbon dioxide in A. sexdens nests in the field is higher than in those in the soil, due to the production of CO2 by the fungus garden and colony.

First record of Cyphoderus innominatus Mills, 1938 (Collembola: Paronellidae) in Early Colonies of the Leaf-cutting Ant Atta sexdens

Cyphoderus innominatus Mills, 1938 (Collembola: Paronellidae) was first observed in early colonies of Atta sexdens leaf-cutting ants (Hymenoptera: Formicidae). The colonies were collected on February 6, 2019, from a transition area between the Atlantic Forest and the Cerrado, located in the municipality of Botucatu, São Paulo, Brazil. A total of four colonies collected had an average population density of 227 ± 212 C. innominatus individuals, and most of the latter were found in peripheral areas inside the fungus-garden-growing chamber of the colony. In addition, we observed a possible defensive behavior on the part of workers when C. innominatus individuals were present in the fungus garden chamber. Thus, this is the first record of C. innominatus living in association with early colonies of A. sexdens. Cyphoderus innominatus Mills, 1938 (Collembola: Paronellidae) foi observado pela primeira vez nas primeiras colônias de formigas cortadeiras Atta sexdens rubropilosa , Forel, 1908 (Hymenoptera: Formicidae). Essas colônias foram coletadas em 6 de fevereiro de 2019, em uma área de transição entre a Mata Atlântica e o Cerrado, localizada no município de Botucatu, São Paulo, Brasil. Um total de quatro colônias coletadas teve uma densidade populacional média de 227, de C. innominatus , ea maioria dos últimos foram encontrados em áreas periféricas dentro da câmara de cultivo do jardim de fungo da colônia. Além disso, observamos um possível comportamento defensivo por parte dos trabalhadores quandoC. innominatus estava presente presentes na câmara do jardim de fungos. Assim, este é o primeiro registro de C. innominatus vivendo em associação com colônias iniciais de A. sexdens rubropilosa .

Mortality of leaf-cutting ants with salicylic acid

Strategies for the control of leaf-cutting ants have mainly involved granular baits based on fipronil and sulfluramid as active ingredients, which are commonly coated with attractive citrus-based substances. Their constant use and the lack of alternatives in the market may favor the perception of these substances by ants, causing rejection for foraging and consequent difficulty in their control. In this respect, this study examined the mortality of leaf-cutting ants of the genera Atta and Acromyrmex subjected to direct application with dry powders, in laboratory conditions. As a preliminary treatment, a commercial antiseptic talc powder (C. A. P. T.) was used, followed by isolated treatments that corresponded to its components with potential insecticidal action, namely, salicylic acid, sulfur, boric acid, zinc oxide, in addition to an inert talc powder (Quimidrol®) as the control. For each treatment, 40 (worker) ants, whose activity was reduced due to remaining in a refrigerator prior to the treatment, were placed in transparent crystal polystyrene (‘Gerbox’ type) and were sprinkled with a salt shaker. The ants were kept at 25 ± 2 °C, under a 12-h photophase, and cumulative mortality was recorded every 24 h, considering dead ants as those that were unable to maintain the natural position of their body, i.e., even dying ants were considered dead when they exhibited no reaction when touched by a paintbrush. When sprinkled on ants, C. A. P. T. causes 40% mortality in both species 24 h after application. Subsequent studies of the components of this commercial product have found that when sprinkled on both Atta sexdens rubropilosa and Acromyrmex crassispinus, salicylic acid causes 100% mortality of workers in the first 24 h. This result provides a new prospect of control through a low environmental-impact product, representing an alternative for control in nests in the field that can contribute to the integrated control of ants.

Comportamento forrageiro de formigas cortadeiras Atta sexdens piriventris Santschi, 1919, em ambiente de Campos de Altitude no Sul do Brasil

Na Microrregião dos Campos de Lages, Santa Catarina, as condições edafoclímaticas, associadas à vegetação típica desta região podem particularizar o comportamento forrageiro de formigas cortadeiras Atta sexdens piriventris, diferentemente das já relatadas para outros locais. Este trabalho teve por objetivo a estudar a bioecologia de forrageamento A. sexdens piriventris que ocorrem naturalmente na Microrregião dos Campos de Lages. Desta forma, formigueiros da espécie A. sexdens piriventris foram localizados de forma aleatória, através de características morfológicas dos indivíduos, e da aparência com aspecto de terra lavrada superficial dos formigueiros. Em cada formigueiro selecionado, foi realizado o levantamento das espécies vegetais preferidas para o forrageamento. Amostras das espécies vegetais, ou partes vegetativas forrageadas foram herborizadas e posteriormente classificadas e identificadas. As características edafoclimáticas da Microrregião dos Campos de Lages, particularizam o comportamento forrageiro e de nidificação apresentado por formigas cortadeiras A. sexdens piriventris. Foram identificadas 68 espécies de plantas distribuídas em 27 famílias botânicas, dentre as utilizadas para o forrageio. Plantas das famílias Poaceae e Asteraceae foram as mais utilizadas no forrageamento por formigas A. sexdens piriventris, sendo a espécie Baccharis trimera (Asteraceae) a mais forrageada. Formigueiros A. sexdens piriventris estavam presentes preferencialmente em área de borda de ambientes.