Toxicity of Cipadessa fruticosa to the leaf-cutting ants Atta sexdens rubropilosa (Hymenoptera: Formicidae) and their symbiotic fungus

Crude extracts from fruits, branches and leaves of Cipadessa fruticosa were assayed on Atta sexdens rubropilosa workers and their symbiotic fungus Leucoagaricus gongylophorus. The results showed that the majority of the extract tested reduced significantly (p < 0.05) the survival of the workers comparable to the neem oil. In addition, the dichloromethane extract from fruits and the hexane extract from branches of C. fruticosa inhibited in 80% the development of the symbiotic fungus. The hexane and dichloromethane extracts from fruits of C. fruticosa were fractionated and their fractions were subjected to new bioassays. Several fractions showed relevant activity on ants, but none of them inhibited significantly the fungal growth. The possibility of controlling leaf-cutting ants in the future using C. fruticosa is discussed.

Assessment of microfungi in fungus gardens free of the leaf-cutting ant Atta sexdens rubropilosa (Hymenoptera: Formicidae)

The purpose of this study was to determine the microfungi present in young nests of Atta sexdens rubropilosa when the fungus gardens were deprived of worker ants. The results were compared with another study in which worker ants had been killed by using toxic baits, and some species such as Acremonium kiliense, Escovopsis weberi, Moniliella suaveolens and Trichoderma sp. were confirmed among the most common inhabitants of this microenvironment, but differences in composition and proportion of species were observed. The importance and the role of these and other species of fungi within the symbiosis are discussed.

Leaf-cutting ants toxicity of limonexic acid and degraded limonoids from Raulinoa echinata. X-ray structure of epoxy-fraxinellone

Phytochemical survey of roots extracts of the South Brazilian endemic plant Raulinoa echinata Cowan, Rutaceae led to the isolation of known degraded limonoids: fraxinellone, fraxinellonone and epoxy-fraxinellone. The latter was previously isolated also from the stems, but the relative configuration could not be solved by NMR experiments. This paper deals with the X-ray diffraction analysis of epoxy-fraxinellone and its toxicity to leaf-cutting ants, describes the isolation of fraxinellonone and fraxinellone for the first time in Raulinoa. Epoxy-fraxinellone showed no toxicity to the leaf-cutting ants (Atta sexdens rubropilosa). The limonoid limonexic acid, isolated from stems, presented high toxicity to the leaf-cutting ants, diminishing considerably their longevity. ©2005 Sociedade Brasileira de Química.

The hypopharyngeal gland of leaf-cutting ants (Atta sexdens rubropilosa) (Hymenoptera: Formicidae)

The social behavior of ants is controlled by means of dynamic interactions between the environment and the individuals, mainly through pheromones. Among the exocrine glands is the hypopharyngeal gland (HG), located laterally over the pharyngeal plate. The present work aimed to describe and compare the HG in the different castes of the leaf-cutting ant Atta sexdens rubropilosa Forel 1908. The HG of different castes showed similar morphology varying only in relation to the secretory cell number. The secretory intracellular reservoir presented positive reaction to Xylidine Ponceau and P.A.S, indicating the presence of protein and polysaccharides in the secretion. Therefore, we suggest that the function of this gland would be the production of digestive enzymes and/or some sort of mucus, which, together with the secretions produced by the salivary glands of the thorax, would be related to the production of saliva.

Cutting characteristics of dental diamond burs made with CVD technology

The aim of this study was to determine the cutting ability of chemical vapor deposition (CVD) diamond burs coupled to an ultrasonic dental unit handpiece for minimally invasive cavity preparation. One standard cavity was prepared on the mesial and distal surfaces of 40 extracted human third molars either with cylindrical or with spherical CVD burs. The cutting ability was compared regarding type of substrate (enamel and dentin) and direction of handpiece motion. The morphological characteristics, width and depth of the cavities were analyzed and measured using scanning electron micrographs. Statistical analysis using the Kruskal-Wallis test (p < 0.05) revealed that the width and depth of the cavities were significantly greater when they were prepared on dentin. Wider cavities were prepared when the cylindrical CVD bur was used, and deeper cavities resulted from preparation with the spherical CVD bur. The direction of handpiece motion did not influence the size of the cavities, and the CVD burs produced precise and conservative cutting.

Toxicity of Azadirachta indica to leaf-cutting ant Atta sexdens rubropilosa (Hymenoptera: Formicidae)

The leaf-cutting ants are responsible for great economical damages in cultivated areas, and because of this characteristic, they have aroused the interest of researchers around the world. Thus, extracts of neem (Azadirachta indica, A. Juss) were tested through ingestion and contact experiments to investigate their toxicity to Atta sexdens rubropilosa workers. Crude extract of neem seed oil was toxic to the ants by ingestion in all concentrations tested but no toxicity was observed in contact experiments. However, crude extract of neem seed paste produced a significant toxicity to workers by ingestion and by contact.

Toxicity of straight-chain fatty acids to leaf-cutting ants Atta sexdens rubropilosa (Hymenoptera: Formicidae) and the symbiotic fungus Leucoagaricus gongylophorus

This work determined toxicity and attractiveness of straight-chain fatty acids (C 5 to C 12) to Atta sexdens rubropilosa (Forel) workers. The effect to the symbiotic fungus, Leucoagaricus gongylophorus (Singer) Möller, was also tested with the fatty acids C 6 to C 12. A strong mortality of leaf-cutting ants that were fed with an artificial diet containing fatty acids C to C at concentrations above 1.0 mg.ml -1 was observed. Rice flakes impregnated with solutions of these fatty acids were repellent to leaf-cutting ants. Contact experiments showed that treatments with C 6 and C 7 at concentration of 100 mg.ml -1 significantly reduced the survival rate of leaf-cutting ants. The fatty acids C 8 to C 11 were toxic to leaf-cutting ants when topically tested at concentration of 200 mg.ml -1. In relation to the fungus' bioassays, the fatty acids C 6 to C 12 at concentration of 0.1 mg.ml -1 inhibited 100% of the fungal development. Although when the concentration was reduced by half no inhibition effects were observed. The results showed that straight-chain fatty acids have desirable properties for controlling leaf-cutting ants since they directly interfere with both organisms of the symbiotic relationship. The potential of fatty acids as well as ways to control leaf-cutting ants with these compounds are discussed in this article.

Photodegradation of soluble and emulsive cutting fluids using TiO 2 as catalyst

This paper describes results of the photo-degradation of three types of soluble and emulsive cutting fluids in an aqueous medium, using TiO2 as catalyst in suspension and UV radiation. The TiO2 proved to be an effective catalyst for the degradation of the cutting fluids investigated. The degradation rate depends on pH and nature of the fluids. The best performance of catalyst was observed at pH 8.0 for all the fluids when most of 70% of the organic load was decomposed. ©2006 Sociedade Brasileira de Química.

The role of workers in transferring queen substances and the differences between worker castes in the leaf-cutting ant, Acromyrmex subterraneus brunneus (Hymenoptera: Formicidae)

The present study focused on the relationship between the queen and workers in Acromyrmex subterraneus brunneus colonies mediated by the possible transfer of substances from the fertile to the sterile caste. The queens were submitted to different situations of physical limitation, i.e., they were kept isolated in cages with holes that only permitted the entry of workers but left the queen isolated. A tracer (water-soluble dye) was applied to the pronotum and gaster of the queen and its dispersal among workers was analyzed. The results demonstrated that the minor sub caste (0.7-0.9 mm) passed on the dye through allogrooming and self-grooming, or transferred the dye through trophallaxis to the major sub caste (1.2-2.0 mm) when they were not in direct contact with the queen. These findings indicate the communication and probable transfer of substances from the queen to the workers, as well as a substance transfer between workers.

Scanning electron microscope assessment of several resharpening techniques on the cutting edges of gracey curettes

Aim: Treatment of periodontal diseases is based on efficient scaling and root planing (SRP) and adequate maintenance of the patient. The effectiveness of SRP is influenced by operator skill, access to the subgingival area, root anatomy, and the quality and type of instrument used for SRP. The aim of this study was to evaluate the cutting edges of Gracey curettes after manufacturing and after resharpening using several techniques. Methods and Material: The cutting edges of a total of 41 new #5-6 stainless steel Gracey curettes were evaluated blindly using scanning electron microscopy (SEM). The quality of the cutting edges was evaluated blindly by a calibrated examiner using micrographs. Data were analyzed using a Kruskal Wallis test and nonparametric two-way multiple comparisons. Results and Conclusions: Different sharpening techniques had significantly different effects on the sharpeness of cutting edges (p<0.05). Sharpening by passing the lateral face of curettes over a sharpening stone and then a #299 Arkansas stone produced a high frequency of smooth, sharp edges or slightly irregular edges between the lateral and coronal faces of the curettes. Sharpening by passing a blunt stone over the curette's lateral face produced the poorest quality cutting edge (a bevel). Sharpening of the coronal curette face produced extremely irregular cutting edges and non-functional wire edges. Sharpening with rotary devices produced extremely irregular cutting edges.

Dispersal of the delayed action insecticide sulfluramid in colonies of the leaf-cutting ant Atta sexdens rubropilosa (Hymenoptera: Formicidae)

Toxic baits are the most used control method for leaf-cutting ants due to their high effectiveness and because they are considered the safest for humans. Taking into account that the importance of leaf-cutting ants as pests, knowing the process by which dispersal and worker contamination is achieved becomes essential to understand several aspects about the functioning of a bait-borne AI (active ingredient) used in toxic baits. It has been established that an effective toxic bait should have a delayed- action AI, but its dispersion among the different sizes of workers is unknown. Workers of different sizes are involved in quite different tasks such foraging, cultivation of symbiotic macrofungus or control of deleterious microfungi. Therefore, we prepared a toxic bait containing the delayed-action AI sulfluramid and a dye (Rhodamine B) as an AI tracer in order to study dispersal and contamination in colonies, evaluated at different periods and in relation to different workers' sizes. Both field and laboratory colonies were evaluated. The great level of contamination, about 50% at 24 hours, in all sizes of workers demonstrates that worker contact with toxic bait is intense within this period. The distribution in field and laboratory colonies was similar. This contamination pattern is probably enough to cause the colony to die because of contamination of smaller workers, leading to the loss of control of the aggressive microfungi, which can quickly overgrow the symbiotic fungus culture. The dispersal dynamics of AI in leaf-cutting ant workers is important for investigations on the mode of action of this insecticide in the colony, and as a reference in future studies, such as those attempting to reduce the concentration of AIs in baits to reduce their environmental impact, or for facilitation of new AI screening.

Influence of grinding on the roundness, residual stresses and microstructure of VC131 steel analysed by varying the type of cutting fluid

This paper by R. E. Catai, E. C. Bianchi, P. R de Águia and M. C. Alves reports on the results of an analysis made of roundness errors, residual stresses, and SEM micrographs of VC131 steel. The analysis involved workpieces ground with two types of cutting fluid: synthetic cutting fluid and emulsive oil. In this study, the cutting parameters were kept constant while the type of cutting fluid was varied. The amount of cutting fluid injected in the process was also varied, aiming to identify the ideal amount required to obtain good results without causing structural damage to the workpiece. The SEM analyses of roundness errors and residual stresses revealed that, of the two cutting fluids, emulsive oil provided better tensions due to its greater lubricating power.

Comparative study on turning CI and CGI using silicon nitride cutting tools

There has been a great interest for improving the machining of cast iron materials in the automotive and other industries. Comparative studies for tool used to machine grey cast iron (CI) and compacted graphite iron (CGI) on dry machining were also performed in order to find out why in this case the tool lifetime is not significantly higher. However the machining these materials while considering turning with the traditional high-speed steel and carbide cutting tools present any disadvantages. One of these disadvantages is that all the traditional machining processes involve the cooling fluid to remove the heat generated on workpiece due to friction during cutting. This paper present a new generation of ceramic cutting tool exhibiting improved properties and important advances in machining CI and CGI. The tool performance was analyzed in function of flank wear, temperature and roughness, while can be observed that main effects were found for tool wear, were abrasion to CI and inter-diffusion of constituting elements between tool and CGI, causing crater. However the difference in tool lifetime can be explained by the formation of a MnS layer on the tool surface in the case of grey CI. This layer is missing in the case of CGI.

Mexico: export promotion policies on the cutting edge

Includes bibliography

Development of a prototype for measuring plantar forces

Studies on the distribution of plantar pressure between the sole of the foot and the ground were developed before the 19th century. Currently, the most often employed plantar pressure measurement systems are Pedar® and FScan®, which have restrictions such as operational difficulty and high cost. In the present study, a device was constructed from two pressure plates capable of measuring plantar forces in discreet areas of the feet at a low cost, using strain-gages attached to sixteen strategic points of the mechanical elements. Sixteen prismatic beams were soldered to each frame, for which the free extremity of each beam represented a specific point of the foot. Two strain gauges were attached to each beam - one near the upper fixed extremity and the other near the lower fixed extremity. Using a Wheatstone bridge electric circuit, the gauges were used to measure the force acting on the extremity of the beam. Precision and accuracy of the prototype was about 10%. In some measurements, accuracy was 2%. The low precision and accuracy were mainly due to the restrictions of the available equipment, which only permitted four measurements at a time. Thus, it was necessary for participants to stand on the plates four separate times, which signified possible changes in the position of the feet on the pressure plates. Despite some limitations, the aim was achieved. The prototype has been used in some studies and represents a contribution to biomechanics, demonstrating the viability of using strain gauges.