The nest architecture of the ant, Pheidole oxyops Forel, 1908 (Hymenoptera : Formicidae)

Pheidole oxyops builds subterranean nests, with an external architecture that is distinctive and easily recognizable by its wide and specific entrance hole, measuring up to 12.2 cm in diameter, denoting a pitfall-trap. In order to study the nests'internal architecture, seven nests were excavated; four were identified with neutral talc, while the others were cast in cement and then excavated. Measurements were made in order to gain a better understanding of their structures, and a photographic documentation was obtained as well. The excavations revealed that the nests are perpendicular relative to the ground, beginning with a cylindrical channel with a mean length of 13.5 cm, containing irregular formations, and whose diameter becomes progressively narrower until the first chamber is formed. As the channel continues, dish-like chambers appear, interconnected by channels that become progressively narrower and longer, while the chambers are arranged at greater distances from each other as nest depth increases. Both channels and chambers are located on the vertical projection of the entrance hole. Nests may reach a depth of up to 5.09 m, with a number of chambers ranging between 4 and 14.

Physical resistance as a criterion in the selection of foraging material by Acromyrmex subterraneus brunneus Forel, 1911 (Hym., Formicidae)

Leaf-cutting ants forage on a wide variety of plant species using the physical and chemical characteristics of the plants as a selection criterion. In order to determine the influence of the physical factor on the selection of foraging material, inert materials such as floral sponge, polystyrene, plastic and clay, which possess different degrees of physical resistance to cutting, were offered simultaneously to five Acromyrmex subterraneus brunneus colonies, and assessed 12 and 24 h after foraging. No substrate selectivity was observed during foraging. Physical resistance was used as a decision criterion for the incorporation or return of the foraged material. This fact suggests the existence of a second time of selection of the foraged material inside the colony during cultivation of the symbiontic fungus.

Worker laying in leafcutter ant Acromyrmex subterraneus brunneus (Formicidae, Attini)

We studied the process of offspring production in queenless colonies of Acromyrmex subterraneus brunneus, and particularly evaluated the ovary development of workers as a function of their age. For this, subcolonies were set up and evaluated at different periods of isolation from the queen (2, 4 and 6 months), besides individually labeled age groups. The subcolonies were assessed according to offspring production and ovaries containing oocytes or not. The evaluations showed worker oviposition and development of males originating from worker-laid eggs. At 2 months'absence of the queen, eggs and larvae were found, with eggs in a higher proportion than larvae. After 4 months, the proportion of eggs had reduced while larvae had increased, and a pupa was found in one subcolony. At 6 months, besides a higher share of larvae, one pupa and one adult male were found. Dissection of workers revealed ovaries containing oocytes during the periods of evaluation. Only a group of medium-sized and large workers, 23.3%, 20.9% and 37.5% of the population from each period assessed in queenless subcolonies respectively, presented developed oocytes in the ovary. The same was observed in colonies with a queen, with 17.6%, 19.6% and 7.8% of the group of dissected workers from each time period, respectively. With respect to worker age, we observed by dissection of the ovary, that the greatest percentage of individuals with ovarioles containing oocytes occurred at 45 days (6 weeks) up to 90 days (12 weeks). These results probably are associated with the workers reproduction and the laying of trophic and reproductive eggs in colonies with and without a queen; these eggs have distinct functions in each situation.

The influence of the scout upon the decision-making process of recruited workers in three Acromyrmex species (Formicidae : Attini)

We examined how the information communicated by a scout worker influences the plant species transported by recruited workers in Acromymex balzani, Acromyrmex rugosus, and Acromyrmex crassispinus, three species of leaf-cutting ant that have different substrate and habitat preferences. We verified that certain plant species were more likely to be transported than others and that recruitment occurs. We found that recruited workers were more likely to transport non-preferred plant species when they were recruited to these by scout workers. The results suggest that the scout worker can communicate information about plant identity to recruited workers, but that recruited workers integrate the information communicated with their own experience during the decision-making process. (C) 2004 Published by Elsevier B.V.

Evaluation of the adequacy of diflubenzuron and dechlorane in toxic baits for leaf-cutting ants (Hymenoptera : Formicidae) based on formicidal activity

Studies assessing the characteristics of active ingredients (AIs) of toxic baits for leaf-cutting ants are still scarce, although the need for a delayed action of these compounds on adult workers has been well accepted (mortality <= 15% at 24 h and <= 90% at 21 days). Therefore, we determined the insecticidal action of two AIs used in commercial baits, diflubenzuron and dechlorane, over time in workers, and discussed the control of colonies in relation to the existing literature. Dechlorane presented excellent insecticidal activity with a delayed action at all concentrations tested, although its commercial use has been prohibited due to its organochlorine nature. In contrast, diflubenzuron did not cause significant mortality or symptoms of intoxication, indicating that the successful cases reported with the use of baits containing this AI were in fact due to an accidental contamination with dechlorane. We comment about the ineffectiveness of diflubenzuron on alternative targets, i.e., young forms and the mutualistic fungus, supporting the concept that the AI needs to a have a delayed action on adult workers.

Filamentous fungi found on foundress queens of leaf-cutting ants (Hymenoptera: Formicidae)

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Relationship Between Population Size and Symbiont Fungus Culture Volume in Colonies of Acromyrmex balzani (Hymenoptera: Formicidae)

In order to quantify the population of Acromyrmex balzani Emery, 1890 nests and to verify whether the population dynamic of the colony is correlated with the symbiont fungus volume, the principal energy source of the colony, five nests located in grassland areas were evaluated. The nests were sprayed with neutral talcum powder to improve visualization and digging. The symbiont fungus and the entire population existent in the chambers were collected. The mean fungus volume and total nest population in excavated nests were, respectively, 74.76 ml and 1,095 individuals. Simple linear correlation analysis verified that the fungus volume grew proportionally to the number of individuals. Despite the correlation between fungus volume and population dynamic of colonies, the factors that determine this relationship are little known since other microorganisms live in association with the colony.

Geographic Distribution and Population Estimate of Leaf-cutting Ants of the Genus Acromyrmex (Hymenoptera: Formicidae) in Southwestern Bahia

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Growth of the Symbiotic Fungus of the Grass-cutting Ant Atta capiguara (Hymenoptera: Formicidae): Effect of Grass Extracts

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Selectivity of Workers of the Grass-Cutting Ants Atta bisphaerica and Atta capiguara (Hymenoptera: Formicidae) to Vegetable Oils

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Internal Architecture and Population Size of Acromyrmex subterraneus molestans (Hymenoptera, Formicidae) Nests: Comparison Between a Rural and an Urban Area

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Growth of populations and the fungus garden of Atta sexdens rubropilosa (Hymenoptera, Formicidae) response to foraged substrates

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Nota sobre a biologia de "Microdon tigrinus" (Diptera: Syrphidae), parasito social de "Acromyrmex coronatus" (Hymenoptera: Formicidae)

The fly of the syrphid Microdon tigrinus is a specific social parasite of leaf-cutting ant, Acromyrmex coronatus. Six colonies of Acromyrmex coronatus were collected in plastic containers, which there was a layer of 1 cm of plaster, with the purpose of maintaining the humidity of fungus culture. Larvae of social parasite were separate for the establishment of instars number, through morphometric study. The data were measured of 165 larvae, using spiracle (length (Ls), width (Ws) and distance between spiracle (Ds)). After that, the morphometric data obtained for the larvae were submitted to cluster analysis by Wong's hybrid method, which produces the adequate number of groups through pseudo F-statistics and pseudo t-squared statistics. The three morphometric variables studied permitted grouping of larvae into the following three distinct groups: cluster 1 [long dash] consisting of 55 larvae (Ls=0.177[plus or minus]0.026, Ws=0.163[plus or minus]0.030, Ds=0.052[plus or minus]0.008 mm); cluster 2 - consisting of 20 larvae (Ls=0.631[plus or minus]0.065, Ws=0.630[plus or minus]0.049, Ds=0.065[plus or minus]0.018 mm); cluster 3 - consisting of 90 larvae (Ls=1.294[plus or minus]0.062, Ws=1.308[plus or minus]0.069, Ds=0.140[plus or minus]0.018 mm). of the all couples, only 1 obtained success in the mating, and the female, after 24 hours, began the oviposition. The female layed 76 eggs in a period of 6 days, after that, her death. The larvae emerged in the seventh day (incubation period [plus or minus] 7 days). From 76 eggs, 54 were viable, with a viability of 71.05%. This study contributes to the knowledge of Microdon tigrinus biology of, a social parasite poorly studied in Brazil.

Aloetismo em Acromyrmex subterraneus brunneus Forel (Hymenoptera, Formicidae), durante o forrageamento, cultivo do jardim de fungo e devolução dos materiais forrageados

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Characterization of Acromyrmex subterraneus brunneus (Hymenoptera: Formicidae) young nests in a fragment of the Neotropical Forest

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)