Spatial distribution of nests of Acromyrmex crassispinus (Forel) (Hymenoptera: Formicidae) in Pinus taeda plantations

The spatial distribution of insects is essential to perform control strategies, to improve sample techniques and to estimate economic losses. We aimed to determine the spatial distribution of nests of Acromyrmex crassispinus (Forel) in Pinus taeda plantations. The experiments were carried out in P. taeda plantations with different ages (treatments: recently-planted, three and six-year old plants). The study took place in Rio Negrinho and in Três Barras, SC. Three plots of one hectare were delimited in each treatment, and plots were divided in 64 sample units. The analysis of the dispersion index [variance/mean relationship (I), index of Morisita (Iδ) and k exponent of negative binomial distribution] showed that the majority of the samplings presented random distribution. Among the three distributions of probabilities studied: Poisson, positive binomial and negative binomial, the Poisson distribution was the best model to fit the spatial distribution of A. crassispinus nests in all samplings. The result was a random distribution in the plantings of different ages.     

Cytogenetic characterization of the ant Trachymyrmex fuscus Emery, 1934 (Formicidae: Myrmicinae: Attini) with the description of a chromosomal polymorphism

The genus Trachymyrmex is a key group in the tribe Attini because of its close phylogenetic relationship to leaf-cutter ants, Acromyrmex and Atta. Cytogenetic data are only available for five taxa of Trachymyrmex, with chromosome numbers of 2n = 12, 18, 20 and 22, and morphology with predominantly metacentric chromosomes. The aim of the present study was to characterize the karyotype of the ant Trachymyrmex fuscus Emery, 1934, by means of the number and morphology of its chromosomes, heterochromatin pattern, CMA₃ and DAPI fluorochromes in the population of two nests collected at Paraopeba, state of Minas Gerais, Brazil. Nineteen females presented 2n = 18 chromosomes (16m + 2sm) and a single male presented n = 9 (8m + 1sm). A size chromosomal polymorphism involving the short arm of the submetacentric pair was confirmed by statistical analysis, with three character conditions: heterozygous SB (with a difference in size between the short arms), standard SS (smaller short arms) and homozygote BB (bigger short arms). In the first nest, both SB and SS workers were observed. The other nest contained heterozygous (SB), homozygous (BB), and a male carrying the B chromosome (larger size). The presence of heterochromatin on all centromeric and pericentromeric chromosomes of T. fuscus suggests that the size difference observed in the submetacentric pair in the SB and BB workers is not related to the heterochromatin but to a duplication of euchromatic regions through intra- or inter- chromosomal rearrangements. The fluorochrome CMA₃ matched the C-banding markings, indicating that the heterochromatin is rich in GC base pairs. As far as we know, this is the first chromosomal polymorphism reported in the tribe Attini.     

Dyed baits distribution in nests of Atta sexdens L. (Hym., Formicidae)

Dyed baits distribution in colonies of Atta sexdens was studied so as to test the hypothesis of uniform distribution. Three medium- to large-size (34–90 m²) colonies were used for the experiment; coloured dyed baits material was made available at the foraging orifices, which had previously been mapped out and grouped into three hypothetical sectors. After 24 h the colonies were killed and the nests excavated; the fungus was removed from each of the chambers for observation of the presence or absence of dyed baits. It was shown that coloured material from each of the different sectors was found in all the fungus chambers, thus confirming the hypothesis.     

Substrate distribution in fungus chambers in nests of Atta bisphaerica Forel, 1908 (Hym., Formicidae)

Abstract:  Substrate distribution was studied in three adult colonies of the leaf-cutting ant Atta bisphaerica Forel, 1908 using dye. Some supply holes were mapped using baits made from small plastic straws impregnated with citric pulp. Two holes, equidistant from one another, were then selected in each nest. The colonies were excavated completely 24 h after bait placement. During excavation, fungus chambers were checked for dye. We observed that the dyed baits were distributed in all sectors and at all depths regardless of where the baits had been placed. This supported the hypothesis that toxic baits placed in a single supply hole are uniformly distributed throughout the colony.     

Colony-level single-sex alate production inPheidole ceres andPheidole pilifera (Formicidae: Myrmicinae)

Summary Patterns of colony-level reproductive investment were estimated inPheidole ceres andP. pilifera. Both species exhibited strong degrees of colony-level, single-sex alate production, but differed in the extent to which colonies produced only one sex. The proportion of reproductive investment allocated to males was negatively correlated to the total reproductive allocation in both species.     

Orientation and Communication in the Neotropical Ant Odontomachus bauri Emery (Hymenoptera,Formicidae, Ponerinae)

The Neotropical species Odontomachus bauri employs canopy orientation during foraging and homing. An artificial canopy pattern above the ants is much more effective as an orientation cue than horizontal landmarks or chemical marks. However, both horizontal visual cues and chemical marks on the ground can serve in localizing the nest entrance. Successful O. bauri foragers recruit nestmates to leave the nest and search for food. However, the recruitment signals do not contain directional information. Antennation bouts and pheromones from the pygidial gland most likely serve as stimulating recruitment signals. Secretions from the mandibular and poison gland elicit alarm and attack behavior.     

Raiding behavior of the dulotic antChalepoxenus muellerianus (Finzi) in the field (Hymenoptera: Formicidae,Myrmicinae)

Summary Little information is available regarding the raiding behavior in nature of dulotic ants belonging to the tribeLeptothoracini. Between July 17 and 24, 1991, several raids ofChalepoxenus muellerianus (Finzi) were observed in nature near Tignale/Lago di Garda, Italy. Apparently, this species raids frequently during its summer raiding season (5 raids were observed during 7 days spent observing 8 colonies). A singleChalepoxenus colony sometimes raids more than one host colony more or less simultaneously. Observations during which oneChalepoxenus colony raided another and captured slavemaker brood indicate that intraspecific raids can occur either accidentally, or as a result of competition or territoriality when there is a sufficient dense slavemaker population.     

External and internal structure of Atta bisphaerica Forel (Hymenoptera: Formicidae) nests

Abstract:  This work was carried out to determine the internal and external structures of Atta bisphaerica (Forel) nests. Six nests were excavated and during excavation, all data referring to chambers and tunnels were recorded. Three nests had been internally cement-moulded, which enabled a better view of the chamber and tunnel structures. Atta bisphaerica nests presented a similar structural pattern, varying only in the number of chambers as a function of external mound area. Chambers were spherical with two communication tunnels. Internal tunnels had an elliptical section, sometimes circular, indirectly linked to chambers through ramifications and directly through short tunnels. Entrance holes were linked to the area of highest chamber concentration by tunnels from the elliptical section, which led to the nest in a radial manner. Knowledge of the colony's three-dimensional architecture permits successful application of chemical control processes, reduces the quantity of product applied, and consequently diminishes costs and environmental damage.     

Foraging,recruitment and predation by Decamorium uelense (Sanstchi) (Formicidae: Myrmicinae) on termites in Southern Guinea Savanna,Nigeria

Summary The myrmicine ant Decamorium uelense is a predator of small termites which feed inside their food sources of roots and plant debris. The ant uses a specialized recruitment regime to secure its prey. A scout ant searches for foraging termites and returns to the nest where it recruits a column of 10–30 ants which attack and immobilize the termites. A mass recruitment phase is then instigated, with larger numbers of ants retrieving the prey. The major prey item is Microtermes (consumed at an annual rate of 632 termites m^-2), with other small termites accounting for 0.5% of the total predation. The annual predation of Microtermes in primary savanna woodland by D. uelense removes 74% of the standing population.