Efeitos do potencial alelopático de três leguminosas forrageiras sobre três invasoras de pastagens

Bioassays were carried out to identify and characterize the allelopathic potential effects of forage legumes leucena (Leucaena leucocephala), mineirão (Stylosanthes guianensis cv. Mineirão) and calopogônio (Calopogonium mucunoides) on germination and radicle elongation of the pasture weeds desmódio (Desmodium adscendens), guanxuma (Sida rhombifolia) and assa-peixe (Vernonia polyanthes). Aqueous seeds and shoot extracts were prepared in a concentration of 10% (w/v). The pH and osmotic potential were measured in each extract. The effects of the osmotic potential on the results were calculated considering the regression equations adjusted to the variations of osmotic potential in each parameter and the osmotic potential of the extracts. The results showed that the pH did not constitute in a source of variation of the results. The donor species indicated allelopathic potential that varied in function of donor and receiver species and part of the donor plant. The aqueous shoot extract of mineirão and calopogônio showed inhibition potential higher than the extract from seeds, while for leucena the effects more evident were obtained with the extract from seeds. Comparatively, the radicle elongation was a more sensitive indicator than germination to the effects of the extracts.The receiver species assa-peixe was the less sensitive to the effects of the extract.

Effect of constituents of the foliar wax of Didymopanax vinosum on the foraging activity of the leaf-cutting ant Atta sexdens rubropilosa

Leaf epicuticular waxes may affect substrate selection by leaf-cutting ants, and host recognition by several phytophagous insects. The influence of the crude epicuticular wax of Didymopanax vinosum E. March. (Araliaceae), and its major constituents lupeol and free primary alcohols, on substrate selection by the leaf-cutting ant Atta sexdens rubropilosa Forel, was investigated. Two ant colonies were used in laboratory bioassays. Corn flakes (zea) were impregnated with chloroform solutions of the substances being tested and fed to the adults. One of the colonies gave results, in most of the tests, not significantly different from the controls. The other colony, however, discriminated against the crude wax, a strong deterrent effect being observed from the first of a series of eight trials. The same colony was able to discriminate against lupeol after the second trial. The fraction of primary n-alcohols (22% C28, 66% C30 and 12% C32) deterred feeding only after the fifth trial. The results demonstrate that some constituents of epicuticular waxes may deter the foraging activity of A. sexdens rubropilosa, depending, however, on the colony under observation. It is suggested that lupeol, of the foliar wax of D. vinosum, is an important deterrent to leaf-cutting ants, although with less pronounced effects than those observed in tests with the crude wax.

Susceptibility of Apis mellifera (Hymenoptera: Apidae) to pellitorine, an amide isolated from Piper tuberculatum (Piperaceae)

The acute toxicity of pellitorine, an amide isolated from Piper tuberculatum (Piperaceae) which is studied as a biopesticide in European corner borer, was evaluated on larvae and newly emerged adults of honeybee Apis mellifera by means of contact and ingestion bioassays. Workers in the larval and adult phase were separated in groups, which received pellitorine in different concentrations. The larvae were maintained in their own original cells, receiving feeding and normal care from the nurses. The adults were confined in wooden cages with screens, receiving artificial diet made up of sugar and water (1:1). The concentrations of 40, 200, 1 000, 5 000 and 25 000 ng a.i./individual were obtained diluting pellitorine in 98% ethanol. LD10 values of 39.14, 36.16 and 13.79 ng a.i./insect were determined for larvae, for adults by ingestion and adults by contact, respectively. The honeybee larvae were shown to be highly susceptible to the amide pellitorine.

Trail-Pheromone Specificity of Two Sympatric Termites (Rhinotermitidae) from Southeastern Brazil

Studies on pheromone specificity are of ecological interest in termite biology where different species share the same habitat. In this work we evaluated the role of the trail pheromones as a mechanism for the isolation of sympatric populations of Coptotermes gestroi and Heterotermes tenuis (Rhinotermitidae) in Brazil. Based on our results, we conclude that trail pheromones are potentially capable of separating sympatric colonies of these species. Furthermore, the trail-pheromone specificity found in these species could be explained by quantitative differences of the common component of the trail pheromone. However, secondary components on the trail pheromone may neutralize the quantitative differences of a common component. Activity bioassays showed that synthetic (Z,Z,E) 3,6,8-dodecatrien-1-ol may act as the common component of the trail pheromone of these species. Further studies should focus on the chemical identification of the trails laid by the termites.

Electroantennographic responses of Heterotermes tenuis (Isoptera: Rhinotermitidae) to synthetic (3Z,6Z,8E)-Dodecatrien-1-ol

The subterranean termite Heterotermes tenuis (Isoptera: Rhinotermitidae) is a pest of great importance for the Brazilian economy as it causes serious damages in commercial reforestations of Eucalyptus spp. and sugarcane cultures. (3Z,6Z,8E)-Dodecatrien-1-ol has been identified as a pheromone of some species of subterranean termites. The objective of this research was to synthesize (3Z,6Z,8E)-dodecatrien-1-ol and determine by electroantennographic (EAG) bioassays the selectivity and sensitivity of H. tenius antennae to its whole worker extract and to the synthetic triene alcohol.

Physiological and cellular responses in two populations of the mussel Perna perna collected at different sites from the Coast of São Paulo, Brazil

The physiological conditions of mussels from Ubatuba and Santos and also of organisms transplanted from Ubatuba to Santos were studied by using different techniques. Assays for lysosomal stability were conducted on the haemolymph. Heart rate activity was monitored for 6h. The embryonic development of larvae obtained from the collected mussels was analysed. For all the compared groups of mussels, no significant differences were observed for the cardiac activity monitoring and the embryonic bioassays. The mean Neutral Red (NR) retention time was similar for the animals from Santos and Ubatuba, whereas the organisms transplanted to Santos showed a reduction in the retention time of the dye, indicating damage in the lysosomal membranes. These differences were possibly due to environmental factors, but further investigations are required to confirm this hypothesis.

Oral toxicity of chemical substances found in Dimorphandra mollis (Caesalpiniaceae) against honeybees (Apis mellifera) (Hymenoptera: Apidae)

Dimorphandra mollis is a characteristic plant from Brazilian saP vanna-like vegetation. The pollen of this species could be toxic to bees and the objective of the present investigation was to study the toxicity of methanolic extracts obtained from the flowers, peduncles and stem bark of D. mollis to Apis mellifera workers. For the study, the extracts were incorporated into the diet of the bees for later evaluation of mortality rates. The substances isolated: neoisoastilbin, catechin, astilbin and tannins were tested on adult workers and only catechin did not cause toxic effects. The data obtained in the toxicity bioassays were analyzed statistically by Log Rank test and all methanolic extracts showed significant (p<0.0001) toxic effects. Astilbin is also the major component of pollen grains, and is probably responsible for honeybee mortality during blooming periods.

Astilbin toxicity to leaf-cutting ant Atta sexdens rubropilosa (Hymenoptera: Formicidae)

The toxicity of astilbin, isolated from Dimorphandra mollis, was tested in laboratory ingestion bioassays for the leaf-cutting ant Atta sexdens rubropilosa Forel. Worker ants that were fed an artificial diet daily to which astilbin was added had a higher mortality rate than the controls. The substance astilbin was incorporated into the diet with and without the utilization of a solvent. Results for both methodologies utilized were similar and indicate that astilbin reduces the median survival of ants. All concentrations tested showed toxic effects against ant workers, and the statistical comparison of survivorship rates from control and treated groups was significantly different, confirming the insecticidal properties of the substance astilbin.

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.

Brosimum gaudichaudii Trecul (Moraceae): Da planta ao medicamento

The chemical, biological, pharmacological and toxicological study of plants used in medical treatments by different societies around the world has been intensifying over the years, primarily in the search for new herbal, homeopathic or even allopathic medicines. Motivated by this interest, we are investigating some Brazilian plant species, among them a tree, Brosimum gaudichaudii Trecul (Moraceae), found in Brazil's savannah-like prairies and scrub-forest (cerrado) and mesophytic forest. Several extracts have been made and separated into fractions and some compounds have been isolated - principally coumarins - and their respective structures analyzed by spectrophotometric and other methods. By collaborating with researchers in other fields, we have been able to carry out various bioassays and even basic clinical tests, namely: determination of anti-helminthic, anti-microbial, photosensitizing, anticancer and mutagenic activities, toxicological and pathogenic studies, with the aim of discovering a genuinely Brazilian herbal or homeopathic medicine.

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.

Seletividade de alguns agrotóxicos em uso na citricultura ao ácaro predador Neoseiulus californicus (McGregor) (Acari: Phytoseiidae)

This work was carried out to determine the residual toxicity of the main pesticides used in citrus, on Neoseiulus californicus (McGregor) under laboratory conditions. For this, it was used the residual contact bioassay. Citrus leaves of the variety Pêra were sprayed in a Potter tower. The residual action was evaluated at 2 hours and 1; 3; 5; 7; 10; 14 e 21 days after treatment. Ten adult females of N. californicus were transferred to each ring, together with an enough amount of Tetranychus urticae nymphs and adults to feed the predator. Mortality evaluations were performed at 72 hours after treatment. Bioassays indicate that the pesticides: acrinathrin, deltamethrin, dinocap, sulphur, fenpropathrin, fenbutatin oxide and propargite were innocuous to N. californicus. On the other hand, abamectin, azocyclotin e cyhexatin caused mortalities of 29.8; 32.0 e 34.1%, respectively, two hours after transference. Dicofol, pyridaben and chlorfenapyr were extremely toxic to the predator mite, causing 100% of mortality two hours after the application. This way, to this population of N. californicus, the releases can be performed safely 3 days after the application, except for cyhexatin (5 days), dicofol and pyridaben (14 days) and chlorfenapyr (21 days), without risk of significant adult mortality rates due to the application of pesticides.

Interspecific interactions between Coptotermes gestroi and Heterotermes tenuis (Isoptera: Rhinotermitidae) under laboratory conditions

Coptotermes gestroi and Heterotermes tenuis are termite pests. Both species have cryptic habits, and are known as subterranean termites. The aim of this study was to verify if food availability and alterations in the proportion of soldiers interfere in the interactions between these termites, since the introduced species C. gestroi occupies the same niche as the native species H. tenuis. Different bioassays were conducted in order to evaluate these interspecific interactions. The results showed that C. gestroi presented advantages in the occupation of territory in all bioassays and suggest a higher efficiency of this species in the search for alternative food sources, especially when the number of soldiers was higher than that of H. tenuis. Additionally, it is possible to conclude that food availability and the different proportion of soldiers involved in the interspecific confrontations interfere in the occupation of territory and in the agonistic behavior between these two species of termites.

Toxoplasma gondii in semen of experimentally infected swine

Eight reproductive boars were divided into three groups and inoculated with Toxoplasma gondii [GI (n=3) 1.5×104 oocysts strain P; GII (n=3) 1.0×106 tachyzoites strain RH; and GIII (n=2) non-inoculated control]. Clinical, hematological, parasitemia and serological tests and studies of the parasite in the semen through bioassay and PCR, and in reproductive organs (Bioassay and immunohistochemical analyses) were conducted to evaluate the toxoplasmic infection. Blood and semen were collected on day -2, -1, 1, 3, 5, 7, 9, 11, 14 and weekly up to 84 days post-inoculation (DPI). No clinical or hematimetric alteration was observed in the boars. Parasitemia was detected in one boar inoculated with oocysts at the 7th DPI and in another boar infected with tachyzoites (GII) at the 3rd and 49 th DPI. Serological tests revealed antibodies against T. gondii in animals inoculated with oocysts or tachyzoites at the 7th DPI with dilutions of 1:256 and 1:64, which reached peaks of 1:4096 at day 11 and 9, respectively. The bioassays revealed the presence of the parasite in semen samples of a boar inoculated with oocysts (GI) at 3, 49 and 56 DPI and from two boars infected with tachyzoites (GII), one animal at 5 and two animals at 49 days DPI. Mice inoculated with semen from the control group (GIII) remained serologically negative. PCR analysis showed T. gondii DNA in the semen of Boar 1 and Boar 3 inoculated with tachyzoites and oocysts, respectively. The immunohistochemical tests showed T. gondii in the reproductive organs of Boar 1 and Boar 2, inoculated with tachyzoites and oocysts, respectively. These findings suggest the possible occurrence of venereal transmission of T. gondii in swine.

Laboratory assessment of two active ingredients for control of coptotemes gestroi (Isoptera: Rhinotermitidae)

The subterranean termite Coptotermes gestroi Wasmann (Isoptera: Rhinotermitidae) is a pest of major economic importance in urban environments of southeastern Brazil. Compared to using pesticides for termite control, termite bait products target termites more specifically and also address environmental contamination issues. In this point of view, we performed two different bioassays in order to evaluate the efficacy of boric acid and fipronil against different populations of C. gestroi. The results showed that concentrations between 2000 and 3000 ppm of boric acid caused approximately 100 percent mortality in termites. Concentrations between 0.01 and 0.0001 ppm of fipronil resulted in 100% termite mortality after 2 wk exposure. The data displayed a fast mortality of termites contaminated with fipronil, even with small concentrations, and therefore it is not a suitable product to be used in baits against C. gestroi. The present study showed a delayed toxicity of boric acid against the subterranean termite C. gestroi which suggests a need for further field tests.