Atta Sexdens Rubropilosa Forel Research Articles

Contamination and mortality of leaf-cutting ant workers by the quinone inside inhibitor fungicide after social interactions

Leaf-cutting ants of the genera Atta and Acromyrmex (Hymenoptera: Formicidae) are the most important pests in forest and agricultural plantations and livestock. Toxic baits are the main method to manage these insects. The objective was to determine whether the behavior of allogrooming, touch, and self-grooming among Atta sexdens rubropilosa Forel, 1908 (Hymenoptera: Formicidae) workers disperse the fungicide quinone inside inhibitor and whether this product is toxic to them. This fungicide was applied, topically, in groups of workers and the social interactions between them and their mortality with and without the fungicide were evaluated. The interactions and the quinone inside inhibitor fungicide contamination increased with the number of leaf-cutting ant workers per group. Excessive touches, with subsequent allogrooming, and self-grooming among the ant workers dispersed the quinone inside the inhibitor fungicide causing 100% mortality and indicating its toxicity to this insect. The hypothesis that social interactions contaminated ant colony mates and the toxicity of the fungicide quinone inside inhibitor to workers of the leaf-cutting ant A. sexdens rubropilosa was proven.

Leafcutter Ants in Southern Amazon Forests, Brazil

This study aims to identify the species of leafcutter ants, the infestation rate and the spatial distribution of anthills in forest plantations in Alta Floresta-MT. The samples were collected in five plots, with I and II being a Eucalyptus urophylla × Eucalyptus grandis hybrid plantation, III a consortium of Brazil nuts (Bertholletia excelsa) and rubber tree (Hevea brasiliensis), IV and V plots of Tectona grandis. The size of the anthills were measured, obtaining the area in square meters of loose ground, were classified into size classes I: ≤ 1 m2; class II: 1.1 to 2.9 m2; class III: 3 to 8.9 m2; class IV: 9 to 25 m2 e class V: > 25 m2. To calculate dispersion, the Dispersion (DI) and Morisita Index (IϬ) were used. Only one species was observed in all plots (Atta sexdens rubropilosa Forel, 1908). 838 nests were mapped in the five sampled plots, the total average density of anthills found in the plots was 26 anthills/ha. The average total area of loose soil occupied by anthills was 590.05 m2, the distribution of anthills between size classes showed 86.87% disproportion with the anthills in class I. The distribution of the anthills in the five plots that were evaluated were of the aggregate type, following the Morisita Index and the Dispersion index.

Lethal Effect and Behavioral Responses of Leaf-Cutting Ants to Essential Oil of Pogostemon cablin (Lamiaceae) and Its Nanoformulation.

Leaf-cutting ants belonging to the genus Atta (Formicidae: Myrmicinae) are important pests in agricultural and forest environments. In the present study, we evaluated the formicidal activity of the essential oil of Pogostemon cablin and its nanoformulation on the leaf-cutting ants: Atta opaciceps (Borgmeier, 1939), Atta sexdens (Linnaeus, 1758), and Atta sexdens rubropilosa Forel, 1908. The nanoformulation was developed by magnetic stirring using polyoxyethylene (36%), pure ethanol (36%), essential oil of P. cablin (18%), and water (10%). Bioassays of acute toxicity by fumigation and behavioral bioassays in treated arenas, with and without choice, were performed. The essential oil of P. cablin and its nanoformulation demonstrated efficient insecticidal activity and irritability to ant species. The concentration required to kill 50% of workers varied from 1.06 to 2.10μLL-1, with a mean time to death of less than or equal to 42h. The essential oil of P. cablin and its nanoformulation reduced the displacement and velocity speed of the workers of A. opaciceps and A. sexdens rubropilosa in totally treated arenas. In the bioassays with choices, the three species of ants walked less and at a greater speed on the treated side of arena. This work demonstrates the potential of the essential oil of P. cablin and its nanoformulation to the generation of new formicidal products.

Effects of Diafenthiuron in Toxic Baits on Colonies of Leaf-cutting ants (Hymenoptera: Formicidae)

Dianfenthiuron is a pre-insecticide that can be activated by photolysis, and may be a promising formicide. This study evaluated the effect of diafenthiuron after photolysis in colonies of Atta sexdens rubropilosa Forel, 1908. The experiment was conducted in a completely randomized design with five treatments and five replications: control (no active ingredient), sulfluramid (standard formicide), diafenthiuron (no exposure to UV), diafenthiuron (2h exposure to UV) and diafenthiuron (6h exposure to UV). Toxic baits were applied at a rate of 0.5 g per colony, and we observed the transport and incorporation of the baits into the colonies. A grading scale was used (0 to 4) to measure the cutting of Acalypha L. (Euphorbiaceae) leaves by workers at 2, 7, 14 and 21 days after application (DAA) and we also measured the garden mass (fungus + adult + brood) at 21 DAA in order to check for growth of the fungus culture. Total loading and incorporation occurred one hour after application of the baits. Colonies that received sulfluramid did not transport leaves at 2 DAA. Workers that received baits with D2h showed an average of 20% transport and 55% incorporation of leaves at 21 DAA. The grading scale indicated that treatments D2h and D6h had the lowest averages, 0.80 and 2.00, respectively. The treatments D2h and D6h reduced cutting of leaves and fungus garden mass, but did not kill the colonies of A. sexdens rubropilosa.

Essential Oils of Hyptis pectinata Chemotypes: Isolation, Binary Mixtures and Acute Toxicity on Leaf-Cutting Ants.

Leaf-cutting ants are pests of great economic importance due to the damage they cause to agricultural and forest crops. The use of organosynthetic insecticides is the main form of control of these insects. In order to develop safer technology, the objective of this work was to evaluate the formicidal activity of the essential oils of two Hyptis pectinata genotypes (chemotypes) and their major compounds on the leaf-cutting ants Acromyrmex balzani Emery and Atta sexdens rubropilosa Forel. Bioassays of exposure pathways (contact and fumigation) and binary mixtures of the major compounds were performed. The major compounds identified in the essential oils of H. pectinata were β-caryophyllene, caryophyllene oxide and calamusenone. The essential oils of H. pectinata were toxic to the ants in both exposure pathways. Essential oils were more toxic than their major compounds alone. The chemotype calamusenone was more toxic to A. balzani in both exposure pathways. A. sexdens rubropilosa was more susceptible to the essential oil of the chemotype β-caryophyllene in both exposure pathways. In general, the binary mixtures of the major compounds resulted in additive effect of toxicity. The essential oils of H. pectinata is a raw material of great potential for the development of new insecticides.

Post-Fire Effect of Savannah Vegetation on the Establishment of New Colonies ofAtta sexdens rubropilosa(Hymenoptera: Formicidae)

Establishing their initial colony is probably the most critical moment in the life of leaf-cutting ants. The non-establishment is connected to abiotic and biotic factors, and the high mortality rates of initial colonies are possibly associated with entomopathogenic or antagonistic microorganisms to the symbiotic fungus present in the soil, hosted by these ants. Fire in the vegetation, depending on the intensity, is known to cause significant changes to the soil physical, chemical, and microbiological properties. The impact of a fire in savannah vegetation (Cerrado) on the establishment of early colonies of Atta sexdens rubropilosa Forel (Hymenoptera: Formicidae) was evaluated. For this end, two areas were selected, one where there had been an accidental fire, and a contiguous one with the same size and vegetation characteristics without burning. In these areas and in soil collected in the same areas and stored in the laboratory, females recently fertilized in the nuptial flight were placed to excavate the soil and establish their colonies. Post-fire changes in the soil chemical and microbiological properties were quantified and correlated successfully in the establishment of new colonies of this leaf-cutting ant. Under field conditions, the females of A. sexdens rubropilosa did not show preference for which areas to excavate: the ones that had been burned or the ones that were unburned; under this condition, no colony survived according to the evaluation performed 120 d after the nuptial flight. Under laboratory conditions, the majority of the females excavated the soil, whether it had been burned or not. However, the establishment of initial colonies was significantly higher in soils collected far from the surface and in areas that had not directly been affected by the fire, showing a negative effect of fire on colony establishment under laboratory conditions. ResumoEstabelecer sua colonia inicial provavelmente seja o momento mais critico da vida das formigas-cortadeiras. O nao-estabelecimento esta ligado a fatores abioticos e bioticos e, possivelmente, as altas taxas de mortalidade de colonias iniciais estejam associadas aos microrganismos entomopatogenicos ou antagonicos ao fungo simbionte cultivado por essas formigas presentes no solo. Sabe-se que o fogo na vegetacao, dependendo de sua intensidade, provoca alteracoes significativas nas propriedades fisicas, quimicas e microbiologicas do solo. Assim, neste trabalho avaliou-se o impacto de um incendio em vegetacao de savana (cerradao) no estabelecimento de colonias iniciais de Atta sexdens rubropilosa Forel (Hymenoptera: Formicidae). Para isso, foram selecionadas areas onde ocorreu uma queima acidental e outra, de mesmo tamanho, com mesmas caracteristicas vegetacionais e contigua sem queima. Nessas areas e em solo coletados nessas mesmas areas e acondicionados em laboratorio foram colocadas femeas recem copuladas no dia da revoada para perfurarem o solo e fundarem suas colonias. Alteracoes nas propriedades quimicas e microbiologicas do solo pos-fogo foram quantificadas e correlacionadas com sucesso no estabelecimento de novas colonias dessa formiga-cortadeira. Em condicoes de campo, as femeas de A. sexdens rubropilosa nao apresentaram preferencia para perfurar o solo de areas queimadas ou nao e, nessa condicao, nenhuma colonia sobreviveu, em avaliacao realizada 120 dias depois da revoada. Em condicoes de laboratorio, a maioria das femeas perfurou o solo, independentemente de o solo onde elas foram acondicionadas ter sido queimado ou nao. Entretanto, o estabelecimento inicial de colonias foi significativamente maior em solos coletados distantes da superficie e em areas que nao sofreram acao direta do fogo, o que mostrou efeito negativo do fogo no estabelecimento de colonias no laboratorio. View this article in BioOne

Does Diatomaceous Earth Control Leaf-Cutter Ants (Hymenoptera: Formicidae) in the Eucalyptus Plantations?

Genus Atta includes some of the most important Formicidae leaf cutter ants which cause extensive damage to the eucalyptus plantations. Atta sexdens rubropilosa Forel, one of the chief pests in Brazilian reforestation, can restrict and reduce forest productivity by its intense and constant leaf-cutting activities on plants at all stages. Therefore, the demand for new products to control A. sexdens rubropilosa indicates the study of the utilization of the dry powder formulation of diatomaceous earth (DE) against this pest in the eucalyptus cultivars. The study was conducted using 120 colonies of A. sexdens rubropilosa in Eucalyptus grandis Hill ex. Maiden x Eucalyptus urophylla Blake (Myrtaceae) (urograndis) stand. The randomized block experimental design was used with six treatments (1, 10, 25, and 50 g/m2 of DE, 6.0 g/m2 sulfluramid bait per square meter of loose soil, and the control) with five replications, each with four colonies of this ant. Diatomaceous earth was applied to the active A. sexdens rubropilosa ant holes, and the sulfluramid bait was applied in bulk in a localized manner. The control efficacy of A. sexdens rubropilosa with DE was low, showing values similar to that of the control, and, for this reason, it cannot be used to control this ant. The bait with sulfluramid showed higher efficacy than those of the other treatments.

Diet type modifies ingestion rates and trophallactic exchanges in leaf‐cutting ants

AbstractConventional control of leaf‐cutting ants is mainly carried out by application of solid insecticide baits. However, alternative approaches could increase the efficiency of control methods. Here, we investigated the hypothesis that liquid and semi‐solid baits are more readily ingested by leaf‐cutting ants and are therefore more toxic than solid baits. Furthermore, following increased ingestion rates, ants could perform higher frequencies of trophallactic exchanges with their nest mates, thus increasing dispersal rates within the colony. Each of three diets were offered to Acromyrmex subterraneus subterraneus (Forel) and Atta sexdens rubropilosa Forel (both Hymenoptera: Formicidae) for 1 h under laboratory conditions and subsequently crop volumes were quantified. The highest crop volumes for both species were seen when the diet was offered in liquid form, and the lowest crop volumes were observed after offering solid diets. Survival rates of the ants were monitored following addition of the neonicotinoid insecticide imidacloprid (IMI) to the three diets. The ingestion of liquid and semi‐solid diets + IMI by A. subterraneus resulted in 17 and 6% survival, respectively, whereas these diets caused 100% mortality of A. sexdens. Ingestion of solid diets with IMI resulted in 51% survival of A. subterraneus and 23% survival of Atta workers. Twenty‐three percent of A. subterraneus which had fed on liquid diet carried out trophallactic exchanges, whereas only 10 and 3% of ants carried out trophallaxis when fed on semi‐solid or solid diet, respectively. Lower trophallactic frequencies were observed for A. sexdens, with 13 and 3% of ants that had fed on liquid and semi‐solid diets performing trophallaxis, respectively. The low trophallactic exchange rates following ingestion of solid diets would reduce the dispersal of these compounds throughout the colony. Control strategies using solid baits should be re‐examined in the light of these findings, which indicate the importance of optimizing insecticide ingestion.

Proposed lime stone treatment as pest control fails for the leaf-cutting ant Atta sexdens rubropilosa

The effect of lime stone in controlling the leaf-cutting ant, Atta sexdens rubropilosa Forel, was studied on the fungus reared by the ants and on their behaviour. In the field, lime stone was applied with a pump in nine colonies, which were compared with nine untreated nests. Nine laboratory colonies were used to assess the effect of lime stone on the fungus reared by the ants, both with and without ants. There was no significant difference in the survival between treated and untreated nests with lime stone, both in the field and in the laboratory, although the behaviour of leaf-cutting ants apparently changed in laboratory colonies. The application of lime stone on the fungus sponge without the ants rapidly led to changes in pH and mortality. The application of lime stone did not control leaf-cutting ants contrary to the results reported by other authors. The behaviour of ants may have contributed to the inefficiency of this method of control, because the ants actively removed the lime stone deposited on the fungus. We suggest that alternative control methods be rigorously tested before being recommended.

Increasing Attractiveness of Baits with Venom Gland Extract for Atta sexdens rubropilosa (Forel) (Hymenoptera: Formicidae)

The effect of larval cuticle extract (larval pheromone) and venom gland extract (trail pheromone) on transport of formulated baits by Atta sexdens rubropilosa (Forel) was studied in the field and under laboratory conditions. In the laboratory, we observed the transport to the nest of baits impregnated with 10 μL of venom gland extract (0.01 gland/bait) or 10 μL of larval cuticle extract (0.05 larva/bait). The most transported impregnated bait was then tested in the field placing rubber septa impregnated with 100 mL of extract or with 100 mL of solvent with the baits at 0.2, 1.0, 5.0, and 10.0 m away from the trail and from the nest entrance. Baits impregnated with venom gland extract were transported more often than baits formulated with larval cuticle extract. In field tests, the venom gland extract reduced the time required for ants to detect baits and increased the transport of baits displayed at 0.2 m from the foraging trail or nest entrance. The increase in the transport of impregnated baits and the lower time to be transported might help to reduce the loss of bait in the field and decrease the risk of active ingredient contacts with non-target species.

Influence of caffeine on the survival of leaf‐cutting ants Atta sexdens rubropilosa and in vitro growth of their mutualistic fungus

Leaf-cutting ants collect plant fresh material for the cultivation of their mutualistic fungus. Atta sexdens rubropilosa Forel (Hymenoptera: Formicidae) cause great economic losses through their foraging activity, mainly in agriculture. The main control method is the application of granulated toxic baits incorporated with an active ingredient (AI). The present goal is to evaluate the effect of caffeine on in vitro growth of the mutualistic fungus and on the survival of the leaf-cutting ants, aiming to verify the potential toxicity of this secondary metabolite over these organisms. Three distinct patterns of fungal growth correlated with caffeine concentration were observed: (1) no effect (0.01% caffeine); (2) intermediate growth reduction (0.05% caffeine); (3) drastic growth reduction (0.10 and 0.50% caffeine). The highest caffeine concentration causes fungus death in the first week. As for insect survival, caffeine does not seem to exert any effect. The treatments with diet containing caffeine showed similar values of M50, irrespective of caffeine concentration. As caffeine was shown to reduce growth of the mutualistic fungus of Atta sexdens rubropilosa, but with no conclusive effect on insect survival, a hypothetical explanation for the selection of different Coffea species by this leaf-cutting ant species might be associated with caffeine toxicity to the fungus.

Toxicological and Histopathological Effects of Boric Acid on <I>Atta sexdens rubropilosa</I> (Hymenoptera: Formicidae) Workers

The current study compared the toxicity of different concentrations of boric acid in adult workers of Atta sexdens rubropilosa Forel (Hymenoptera: Formicidae), with toxicological bioassays, and examining the dose-dependent and time-dependent histopathological changes, of the midgut, Malpighian tubules, and postpharyngeal glands. Our results revealed the importance of conducting toxicological bioassays combined with morphological analyses of the organs of ants chronically exposed to insecticides used in commercial ant baits. In vitro bioassays showed that boric acid significantly decreases the survivorship of workers regardless of concentration, whereas the morphological data suggested progressive dose-dependent and time-dependent changes in the organs examined, which were evident in the midgut. The midgut is the first organ to be affected, followed by the postpharyngeal gland and Malpighian tubules. This sequence is in agreement with the absorption pathway of this chemical compound in the midgut, its transference to the hemolymph, possibly reaching the postpharyngeal glands, and excretion by the Malpighian tubules. These progressive changes might be due to the cumulative and delayed effect of boric acid. Our findings provide important information for the understanding of the action of boric acid in ant baits in direct and indirect target organs.

Morphometry of the metapleural gland of workers engaged in different behavioral tasks in the ant Atta sexdens rubropilosa

Abstract The exocrine metapleural gland is unique for ants and is characterized by antibiotic production. This work aimed at comparing (1) the volume of the metapleural gland, (2) the nucleus-cytoplasm relation of the secretory cells and (3) the surface area of the bulla which corresponds to the external part of the gland in workers of Atta sexdens rubropilosa Forel, 1908. The measurements were conducted in medium-sized workers of the following groups: waste processors (workers that manipulated waste), waste removers (workers that transported the waste fragment), foragers and workers inside the fungus garden. We show that the volume of the metapleural gland reservoir is larger in groups that are more exposed to infections.

Características biológicas e comportamentais de Neodohrniphora elongata Brown (Diptera, Phoridae), um parasitóide da saúva Atta sexdens rubropilosa Forel (Hymenoptera, Formicidae)

Foram investigadas as características da biologia e comportamento do forídeo Neodohrniphora elongata Brown, 2001 em relação às operárias do hospedeiro Atta sexdens rubropilosa Forel, 1908. Vinte e quatro fêmeas de N. elongata coletadas no campo foram liberadas, uma por vez, em uma cuba de observação interposta entre um ninho de A. sexdens rubropilosa e uma arena de forrageamento. As moscas realizaram de quatro a cinco vezes mais investidas sem sucesso contra as formigas do que ataques efetivos, quando elas ovipositaram na cabeça das operárias. Houve ataques em 426 operárias e desenvolvimento da larva do parasitóide na cápsula cefálica de 63,8% delas, sendo que emergiram 218 moscas. N. elongata ovipositou nas maiores operárias, ou seja, naquelas com largura da cápsula cefálica de 2,9 ± 0,4 mm, o que parece ser importante para o desenvolvimento do parasitóide, pois o fracasso na formação de pupas ou a não emergência do adulto ocorreram principalmente em formigas com largura da cápsula inferior a 2,9 mm. As moscas que emergiram em laboratório tiveram maior longevidade quando alimentadas com solução de mel 10% do que com solução de mel 50% ou somente água destilada. As fêmeas que emergiram no laboratório exibiram os mesmos comportamentos de voo e ataque das fêmeas do campo, mas não foi possível obter parasitóides de segunda geração. Estudos adicionais devem ser realizados para investigar a adequação de fontes naturais de carboidratos e proteínas sobre a longevidade e reprodução de N. elongata, visando à multiplicação deste e de outros forídeos de saúvas em laboratório.

Mechanism of host recognition in Neodohrniphora elongata (Brown) (Diptera: Phoridae)

Insects can use different cues derived from their host or habitat to localize and identify an appropriate host. We conducted this study to investigate the mechanisms used by Neodohrniphora elongata (Brown) to localize and recognize the host Atta sexdens rubropilosa Forel. Females of the parasitoid N. elongata were collected in the field and tested individually in an observation box. The effect of chemical and visual stimuli, associated with A. sexdens rubropilosa, on the location and acceptance behaviour of N. elongata was verified. The chemical stimuli of the ant workers alone triggered no behavioural response in the phorid. Visual stimuli of the ant were sufficient to trigger behavioural acts related to host localization and recognition in the phorids. The trail pheromone of A. sexdens rubropilosa associated with host visualization increased the total time of inspection of a potential host. Visual cues in motion increased the inspection period, compared to static visual cues. Moving basic morphological configurations, regardless of the degree of complexity, triggered similar inspection behaviour as that observed towards live hosts in N. elongata . The phorids, however, did not identify these incomplete morphological models as hosts when static.

Parasitismo por Neodohrniphora spp. Malloch (Diptera, Phoridae) em operárias de Atta sexdens rubropilosa Forel (Hymenoptera, Formicidae)

Parasitoids of the genus Neodohrniphora Malloch, 1914 generally attack workers of Atta sexdens rubropilosa Forel, 1908 in low ratios. However these attacks alter the foraging rhythm and reduces the number and size of workers as well as increases the number of abandoned plant fragments along the trails. A. sexdens rubropilosa can have a diurnal or nocturnal foraging activity, but it is uncertain if Neodohrniphora spp. attacks workers of this host during the night. The objective of this work was to verify the occurrence of Neodohrniphora phorids attacks and the level of parasitism on workers of A. sexdens rubropilosa under three light levels in laboratory, including the darkness. The levels of illumination were: high-light (0.65 µmol/m3/s); low-light (0.05 µmol/m3/s) and darkness (0.0 µmol/m3/s). Field collected parasitoid females (Neodohrniphora tonhascai Brown, 2001 and Neodohrniphora elongate Brown, 2001) released in laboratory have attacked and parasitized A. sexdens rubropilosa workers only under high-light level. This suggests that these two Neodohrniphora species are not active in the field during the night (darkness) and that visual stimulus could be an essential component to the location and recognition of the host.

Isolation of compounds attractive to the leaf-cutting ant Atta sexdens rubropilosa forel (hymenoptera: Formicidae) from Mabea fistulifera elaiosome

Mabea fistulifera (Euphorbiaceae)is a pioneer plant species with seeds dispersed by the ant Atta sexdens rubropilosa. Since the ants are attracted to the seeds to use its elaiosome as a source of energy, we investigated its composition. The elaiosomes from 13,000 seeds were extracted with a methanol:chloroform mixture (2:1 v/v) and yielded 22% of a residue. This residue was fractionated by column chromatography and its composition determined by infrared spectroscopy and chromatography/mass spectrometry (GC-MS). The elaiosome lipids are constituted mainly by free fatty acids, triacylglycerols and minor quantities of monoacylglycerols or diacylglycerols.

Características químicas do lixo de formigueiros de Atta sexdens rubropilosa (Hymenoptera: Formicidae) mantidos com diferentes substratos

As saúvas (Atta spp.) estão amplamente distribuídas pelo continente Sul-Americano e são consideradas importantes componentes do ecossistema neotropical. Diversos estudos têm demonstrado o efeito de formigueiros no enriquecimento do solo e na facilitação ao estabelecimento de espécies vegetais. Possivelmente o enriquecimento do solo seja devido ao acúmulo de matéria orgânica decomposta em câmaras de descarte (lixo) no interior das colônias. Entretanto, pouco se sabe sobre a composição química do lixo de formigas cortadeiras. O objetivo do presente trabalho foi comparar os teores de nutrientes do lixo produzido por colônias de Atta sexdens rubropilosa Forel (Hymenoptera: Formicidae), em laboratório, mantidas com folhas de duas espécies de plantas. Os tratamentos foram dois tipos de substrato (Acalypha sp. ou Bauhinia sp.), repetidos quatro vezes. Oito colônias foram divididas em dois grupos (n = 4), e cada grupo foi mantido com apenas um tratamento. Após 30 dias de experimento, as amostras de folhas e lixo foram secas em estufa (70 ºC) e submetidas à digestão ácida, para determinação das concentrações de N, P, K, S, Ca e Mg. Diferenças nas concentrações dos macronutrientes entre os tratamentos (lixo ou folha) foram comparadas por meio de ANOVA e teste T. As concentrações de nutrientes no lixo foram sempre maiores do que nas folhas, independentemente da espécie cortada. Folhas de Acalypha sp. apresentaram concentrações significativamente maiores do que folhas de Bauhinia sp. com relação aos teores de P, Ca, Mg e S; entretanto, as concentrações do lixo em todos os formigueiros foram muito próximas, indicando incorporação adicional de nutrientes por meio do fungo, excreções e, ou, cadáveres no lixo. Esses resultados indicam que, independentemente do substrato cortado, o lixo produzido apresenta maiores concentrações de nutrientes do que as folhas, sendo importante locus de reciclagem de nutrientes no ecossistema. O lixo pode ser uma das principais razões para o aumento da concentração de nutrientes em solos de formigueiros.

Determinação do fator de conversão em colônias de Atta sexdens rubropilosa (Hymenoptera: Formicidae) e sua relação com a qualidade do material vegetal cortado

As formigas cortadeiras (Atta e Acromyrmex) são consideradas importantes pragas na agricultura e silvicultura, mas pouco se sabe sobre os reais danos dessas espécies. Uma forma bastante difundida de avaliação do dano é por meio do cálculo da taxa de conversão, dividindo-se o peso do material cortado pelo peso de lixo produzido pelas colônias. Foi levantada a hipótese de que a qualidade do substrato cortado pode influenciar no forrageamento das operárias, alterando a taxa de conversão e dificultando as estimativas de dano. A taxa de conversão de oito colônias de Atta sexdens rubropilosa Forel (Hymenoptera: Formicidae) foi calculada com duas espécies vegetais com diferentes concentrações de lignina e celulose, para testar essa hipótese. Colônias mantidas com folhas de baixa qualidade (razão lignina/celulose elevada) tiveram maior forrageamento e produziram mais lixo. Entretanto, a taxa de conversão das colônias foi semelhante com essas duas plantas (média = 1,54). Esse valor está dentro da variação encontrada para outras espécies no campo (1,5-1,8), indicando um fator semelhante de conversão entre os gêneros Atta e Acromyrmex. O consumo médio de material vegetal, em termos de pesos seco e fresco, de uma colônia de A. sexdens rubropilosa com 4.500 operárias, foi estimado em 520 e 1.100 g/ano, respectivamente.

Efeito de formulações granuladas de diferentes produtos químicos e à base de folhas e de sementes de gergelim, <i>Sesamum indicum</i>, no controle de formigueiros de <i>Atta sexdens rubropilosa</i> Forel, 1908 (Hymenoptera: Formicidae).

Avaliou-se a eficiência de diferentes iscas formicidas comercializadas e de outras fabricadas artesanalmente à base de gergelim, Sesamum indicum, no controle de formigueiros de saúva-limão, Atta sexdens rubropilosa Forel, 1908. O experimento foi realizado em reflorestamento de Eucalyptus camaldulensis com dez anos de idade e dois de rebrota. Foram empregados dez tratamentos, incluindo a testemunha, tendo como ingredientes ativos: clorpirifós, sulfluramida, fipronil, farinha de folhas de gergelim (15%), farinha de sementes de gergelim (10%, 20% e 30%). A verificação da mortalidade dos formigueiros foram realizadas aos 30, 60, 90 e 150 dias após o tratamento. As iscas mais eficientes foram à base de sulfluramida e fipronil, seguida da formulação à base de farinha de folhas de gergelim (15%). As iscas à base de sulfluramida e de fipronil atingiram o controle máximo na avaliação dos 30 dias enquanto as iscas à base de folhas de gergelim (15%) apresentou controle satisfatório só a partir da terceira avaliação, isto é, aos 90 dias. Contudo, os resultados obtidos com a isca à base de folhas de gergelim (15%) são encorajadores, mostrando que estudos posteriores deverão ser realizados.