Effect of the presence of brood and fungus on the nest architecture and digging activity of Acromyrmex subterraneus Forel (Hymenoptera, Formicidae)

ABSTRACT This study investigated the stimuli that trigger digging behavior in Acromyrmex subterraneus during nest building. The hypothesis was that the presence of the fungus garden and/or brood triggers the excavation of tunnels and chambers. For the experiment, the excavation rate of individually marked workers kept in plastic cylinders filled with soil was recorded. Four treatments were applied: (1) 30 medium-sized workers, 5 g fungus garden and 30 brood items (larvae and pupae); (2) 30 medium-sized workers and 5 g fungus garden; (3) 30 medium-sized workers and 30 brood items; (4) 30 medium-sized workers without fungus and brood. After 24 h, morphological parameters of nest structure (length and width of the chambers and tunnels in cm) and the volume of excavated soil were recorded. In contrast to the expected findings, no change in morphological structure, rate of excavation by workers, or volume of excavated soil was observed between treatments, except for tunnel width, which was greater, when no brood or fungus garden was present. Thus, the results do not support the hypothesis that the fungus garden and/or brood are local stimuli for nest excavation or that they mold the internal architecture of the nest. Although this hypothesis was confirmed for Acromyrmex lundii and Atta sexdens rubropilosa, the same does not apply to A. subterraneus. The digging behavior of workers is probably the result of adaptation during nest building in different habitats.

The trade-off between the transmission of chemical cues and parasites: behavioral interactions between leaf-cutting ant workers of different age classes

ABSTRACT Social animals are faced with an intriguing dilemma. On the one hand, interactions between individuals are essential to exchange information and to promote cohesion, while on the other hand such interactions carry with them the risk of catching and transmitting parasites. This trade-off is particularly significant for social insects because low within-colony genetic diversity makes their colonies potentially vulnerable to parasites while frequent interactions are essential to the development of the colonial odor profile necessary for nestmate recognition. Here we investigate whether social interactions between young and old leaf-cutting ant workers show evidence of this trade-off. We find that old workers engage in more selfgrooming and mandibular scraping than young workers, both in keeping with old workers having been more exposed to parasites. In contrast, we find that young workers engaged in more allogrooming than old workers, which seems likely to have a different motivation possibly the transfer of recognition cues. Furthermore, young workers tended to engage in allogrooming with other young workers, although it was the old workers that were most active and with whom allogrooming would seem likely to optimize information or chemicals transfer. This suggests that young workers may be attempting to minimize the risk of parasite transmission during their social interactions. Although limited to behavioral data, these results hint that ant workers may be sensitive to the trade-off between the transmission of recognition cues and disease, and adjust their social interactions accordingly.

LEAF-CUTTING ANTS Acromyrmex niger SMITH, 1858(HYMENOPTERA; FORMICIDAE) USED AS BIOINDICATORS OF AGROTOXICS RESIDUES / Utilización de hormigas cortadoras Acromyrmex niger Smith, 1858 (Hymenoptera; Formicidae) como bioindicadores de residuos de agrotóxicos

Despite the condition of leaf-cutting ant pests in agroecosystems, it is undeniable the benefits they can bring in certain situations or environments. The leaf-cutting ants of the genus Acromyrmex attack mainly leaves of vegetables and fruit trees exposing not only to the agrochemicals used for their control as well as to those used for the control of other pests. Due to the bioindicator potential of environmental quality of the ants and their frequent exposure to agrochemicals such as organophosphates, neonicotinoids and growth regulators insecticide used for pest control, it is necessary to study the sublethal effects that these pesticides may cause. The electrophoresis technique was used to study the activity of esterase isozymes involved in the metabolism of xenobiotics of A. niger , combined with changes in the expression of isozymes after contamination by pesticides. A. niger showed eight regions of esterase activity, which were called EST-1, EST-2, EST-3, EST-4, EST-5, EST-6, EST-7 and EST-8 according to the electrophoretic mobility. As the specificity to ± and b-naphthyl acetate substrates, the Est- 7 and Est-8 may be ified as ±-esterase and the others as ±b esterases. EST-5 is considered an enzyme of the type cholinesterase II and the others are of the type carboxilesterase. The electrophoretic analysis showed partial inhibition to all esterases subjected to the contact with Malathion organophosforate at the concentrations 1 x 10-3 % and 5 x 10-3 %, which may be considered as a biomarker for the presence of residues of this insecticide in the environment. The regression analysis for sublethal effects of the tested pesticides demonstrated correlation between dose and mortality only for Thiametoxam neonicotinoid pesticide.

A pesar de la condición de plaga de las hormigas cortadoras en agroecosistemas, no se pueden negar los beneficios que ellas pueden traer en determinadas situaciones o en determinados ambientes. Las hormigas cortadoras del género Acromyrmex atacan principalmente las hojas de hortalizas y hojas de plantas fructíferas, exponiéndose no solo a los agroquímicos utilizados para su control sino también a aquellos utilizados en el control de otras plagas. Debido al potencial bioindica-dor de la calidad ambiental de las hormigas y su frecuente exposición a los agrotóxicos como organofosforados, neonicotinoides y reguladores de crecimiento, utilizados en el control de plagas, es necesario el estudio de los efectos subletales que estos agrotóxicos pueden causar. La técnica de electroforesis fue utilizada para evaluar la actividad de las isoenzimas esterasas involucradas en el metabolismo de xenobióticos de A. niger , asociada a las alteraciones en la expresión de las isoenzimas después de la contaminación con pesticidas. Acromyrmex Niger demostró ocho regiones de actividad esterasa, las cuales fueron denominadas EST-1, EST-2, EST-3, EST-4, EST-5, EST-6, EST-7 e EST-8 de acuerdo con la movilidad electroforética. En cuanto a la especificación de los substratos ± y b-nafitl acetato, las EST-7 e EST-8 son clasificadas como ±- esterasa y las demás ±b esterasas. EST-5 es considerada una enzima del tipo colinesterasa II y las demás son carboxilesterasas. El análisis electroforético presentó inhibición parcial para todas las esterasas sometidas al contacto con malathion en las concentraciones 1 x 10-3 % e 5 x 10-3 %, que puede ser considerado un biomarcador para la presencia de residuos de este insecticida en el ambiente. El análisis de regresión para el efecto subletal de los pesticidas evaluados demostró correlación entre la dosis y la causa de muerte solo para el pesticida neonicotinoide thiametoxam.

Mandibular and postpharyngeal gland secretions of Acromyrmex landolti (Hymenoptera: Formicidae) as chemical cues for nestmate recognition

Nestmate recognition is fundamental for the cohesiveness of the colony in social insects. Acromyrmex landolti is a higher Attini, a leaf-cutter ant with largest nest and morphological castes. We studied the location of the recognition signal of A. landolti on the whole ant body, the isolation effect on the capacity of nestmaterecognition, and the role of the mandibular (MG) and post-pharyngeal glands (PPG) as putative sources for chemical recognition signals in this species. We performed behavioral bioassays and chemical analyses of MG and PPG glands; MG volatiles in different castes were also characterized. In order to determine the occurrence of nestmate recognition signals, behavioral tests were performed for which the whole body, body parts or gland extracts from a nestmate and an alien worker ant, were placed on the central axis of an active field trail. Besides, the isolation effect of the nestmate chemical signal persistence was evaluated by repeating the experiments with whole ant bodies after 12h, 24h and 48h of isolation. The agonistic behavior of the ants on the trail was classified as inspection, threatening and biting. Gland volatiles were obtained by headspace solid phase microextraction, and PPG by solid sample analyses; and chemical analyses were performed using gas chromatography-mass spectrometry. Workers performed agonistic behaviors more frequently towards non-nestmate whole bodies, body parts and gland extracts, primarily those from the post-pharyngeal glands. Nestmate thoraces odorized with alien extracts were also recognized from aliens. Nestmate recognition ability persists for 12h and 24h after isolation, but decreases after 48h, suggesting that the chemical signal changes over time. Inter-colonial chemical analyses showed no differences in the PPG hydrocarbon profiles, while the relative proportions of MG compounds showed significant differences between colonies. These results showed that nestmate recognition was achieved by MG volatiles. Possibly, the PPG secretion works as a matrix that absorbs MG volatiles. We report, for the first time, some mandibular gland compounds for the genus Acromyrmex and for the tribe Attini group.

El reconocimiento de compañeras de nido es fundamental para la cohesión de la colonia en los insectos sociales. Las señales de reconocimiento de compañeras en Acromyrmex landolti fueron estudiadas mediante bioensayos de comportamiento y análisis químicos de los componentes de la glándula mandibular (GM) y postfaríngea (GPF). Los bioensayos de comportamiento fueron realizados usando cuerpos completos de hormigas, partes del cuerpo y extractos glandulares de GM y GPF de una compañera de nido y una intrusa en el centro de una trilla activa. Los comportamientos agonísticos de las obreras se clasificaron en exploración, ataque y mordida. Las obreras se mostraron más agresivas hacia los cuerpos completos, partes del cuerpo y extractos glandulares de las intrusas que hacia los de las compañeras de nido. Los volátiles glandulares se obtuvieron mediante la técnica de espacio en cabeza con microextracción en fase sólida, y los hidrocarburos de la PPG por análisis de muestra sólida. Se encontró que los volátiles de la GM conforman la señal de reconocimiento. No se encontraron diferencias intercoloniales para los volátiles de la GM. Posiblemente los hidrocarburos cuticulares actúan como una matriz que absorbe volátiles de la GM.

Controle De Acromyrmex laticeps nigrosetosus (Hymenoptera: Formicidae), em eucaliptal no Pará, com Iscas Granuladas com Sulfluramida ou Clorpirifós

This research was developed in an Eucalyptus plantation of Jari Celulose S.A., in Almerin, Pará State, Brazil from September 1996 to January 1997. The objectives were to test the efficiency of two ant baits with sulfluramid and another one with chlorpirifos (at 4, 6, 8 and 10 grams per square meter of ant nest) against Acromyrmex laticeps nigrosetosus Forel (Hymenoptera: Formicidae). Both baits with sulfluramid, in all dosages tested, showed more than 99.0% of transport with no devolution. All ant colonies treated with these baits were dead during the final evaluation while mortality of nests of this ant treated with chlorpirifos ranged from 55.56 to 66.67% for the different dosages tested. The sulfluramid baits can be recomended to control A. laticeps nigroselosus in the humid tropic of Brazil.

Este trabalho foi realizado em reflorestamento de eucalipto da Jari Celulose S.A., no município de Almerim, Pará, de setembro de 1996 a janeiro de 1997. Objetivou-se testar a eficiência de duas iscas granuladas à base de sulfluramida e outra à base de clorpirifós, nas dosagens de 4, 6, 8 e 10 gramas por metro quadrado de formigueiro, para o controle de Acromyrmex laticeps nigroselosus Forel (Hymenoptera: Formicidae). As duas iscas com sulfluramida, nas dosagens testadas, apresentaram acima de 99,0% de transporte e nenhuma devolução. Todos os formigueiros tratados, com essas iscas, estavam mortos na avaliação final, enquanto a eficiência da isca com clorpirifós variou de 55,56 a 66,67%, para as diferentes dosagens testadas. As iscas à base de sulfluramida podem ser recomendadas para o controle de A. laticeps nigrosetosus na região do trópico úmido do Brasil.