Ionizete Garcia da Silva

Selection of Beauveria bassiana and Metarhizium anisopliae isolates to control Triatoma infestans

Twenty three isolates of Beauveria bassiana and 13 isolates of Metarhizium anisopliae were tested on third instar nymphs of Triatoma infestans, a serious vector of Chagas disease. Pathogenicity tests at saturated humidity showed that this insect is very susceptible to fungal infection. At lower relative humidity (50%), conditions expected in the vector microhabitat, virulence was significantly different among isolates. Cumulative mortality 15 days after treatment varied from 17.5 to 97.5%, and estimates of 50% survival time varied from 6 to 11 days. Maintaining lower relative humidity, four B. bassiana and two M. anisopliae isolates were selected for analysis of virulence at different conidial concentrations and temperatures. Lethal concentrations sufficient to kill 50% of insects (LC50) varied from 7.1 x 10(5) to 4.3 x 10(6) conidia/ml, for a B. bassiana isolate (CG 14) and a M. anisopliae isolate (CG 491) respectively. Most isolates, particularly B. bassiana isolates CG 24 and CG 306, proved to be more virulent at 25 and 30 degrees C, compared to 15 and 20 degrees C. The differential virulence at 50% humidity observed among some B. bassiana isolates was not correlated to phenetic groups in cluster analysis of RAPD markers. In fact, the B. bassiana isolates analyzed presented a high homogeneity (> 73% similarity).

Atividade larvicida de taninos isolados de Magonia pubescens St. Hil. (Sapindaceae) sobre Aedes aegypti (Diptera, Culicidae)

Phytochemical study of the larvicidal fractions which were carried out for the first time, isolated of the Magonia pubescens, monitored by the study of efficacy against the 3rd larval instar of Aedes aegypti, in the search of alternatives for the control of that mosquito and to obtain structures susceptible to chemical improving of the activity for the synthetic via of other derived. The fractions with biological activity were monitored chemically through chromatography of thin layer, using as revealing a solution acid of vanillin, analyzed by nuclear magnetic resonance of hydrogen and spectrometry of masses. The bioassays with the fractions were accomplished with five replications, controlled at the temperature of 28+/-1 degrees C, 80+/-5% of relative humidity and 12 h light. The found lethal concentrations of the fraction that it presented the largest potential larvicidal, MP-9, LC50 and LC90, were of 3.1 and 36.6 ppm, respectively. All the experiments were accompanied by a control series, containing the same number of larvae.

Toxicidade do extrato etanólico de Magonia pubescens sobre larvas de Aedes aegypti

Crude ethanol extracted from Magonia pubescens trunks was utilized to prove its effect in the intestinal tract of Aedes aegypti 3rd instar larvae. Exposure times (2, 4, 6, 8, 10, 12, and 13 hours) were tested to verify when the morphological alterations begin to occur, in the intestinal tract of the larvae. The toxic effect of the extract was mainly in the midgut, beginning at the anterior midgut and followed through to posterior midgut. The main alterations observed were partial or total cell destruction, high citoplasmatic vacuolization, increase of subperitrophic space, cell hypertrophy and the epithelium did not maintain its monolayer appearance. The alterations began after four hours of exposure to M. pubescens extract. Observations of tissue sections from larvae treated for different lengths of time revealed a wide variation in the degree of damage between exposure periods and midgut larvae region. The present study provides evidence regarding the mode of action of the M. pubescens extract and suggests its potential utilization as a larvicide to control Aedes aegypti mosquito.

Distribuição geográfica e indicadores entomológicos de triatomíneos sinantrópicos capturados no Estado de Goiás

The geographic distribution of triatomines in Goias and entomological indicators in the home environment are presented: home infestation, home triatomine density and vector infection by Trypanosoma cruzi. The indicators studied were from triatomines captured inside and outside homes in 201 municipalities in the State of Goias, Brazil, between 2000 and 2003. A total of 249,868 home units were investigated and 51,570 triatomines were captured, and 335 specimens were found to be infected with Trypanosoma cruzi. Infestation outside the home was significantly greater than infestation inside the home for the species Triatoma sordida, followed by Panstrongylus megistus. The contrary was observed with the species Rhodnius neglectus, Panstrongylus geniculatus and Triatoma pseudomaculata (p<0.018). There was no significant difference between infestations inside and outside the home for the species Panstrongylus diasi, Triatoma costalimai and Triatoma williami. Only one specimen of Triatoma infestans was captured in the year 2000.The geographic distribution of triatomines in Goias and entomological indicators in the home environment are presented: home infestation, home triatomine density and vector infection by Trypanosoma cruzi. The indicators studied were from triatomines captured inside and outside homes in 201 municipalities in the State of Goias, Brazil, between 2000 and 2003. A total of 249,868 home units were investigated and 51,570 triatomines were captured, and 335 specimens were found to be infected with Trypanosoma cruzi. Infestation outside the home was significantly greater than infestation inside the home for the species Triatoma sordida, followed by Panstrongylus megistus. The contrary was observed with the species Rhodnius neglectus, Panstrongylus geniculatus and Triatoma pseudomaculata (p<0.018). There was no significant difference between infestations inside and outside the home for the species Panstrongylus diasi, Triatoma costalimai and Triatoma williami. Only one specimen of Triatoma infestans was captured in the year 2000.

Influência do período de quiescência dos ovos sobre o ciclo de vida de Aedes aegypti (Linnaeus, 1762) (Diptera, Culicidae) em condições de laboratório

The influence of the period of egg quiescence on the life cycle of Aedes aegypti (Linnaeus, 1762) (Diptera, Culicidae) was studied under laboratory conditions in order to improve the management of vector control. The eggs are known to be the most resistant stages during development, allowing a long survival of the mosquitoes under unfavorable climatic conditions. The experiments were performed in a biological chamber kept at 28 ± 1oC temperature, with 80 ± 5% relative humidity and 12 hours of photophase. Data about the influence of different periods of quiescence on eclosion, larval and pupal development and the developmentals cycle are presented. We observed a highly significant effect of the period of quiescence on larval eclosion. The period of quiescence had no influence on the duration of larval or pupal incubation. Eggs originating from the same period of quiescence showed significantly different periods of incubation The larvae emerged in groups defined by the period of incubation. This group effect was significant during the cycle. In 99.8% of the cycles the variation was determined by incubation.

Larvicidal activity of Copaifera reticulata ducke oil-resin against Culex quinquefasciatus Say (Diptera: Culicidae)

The appearance of resistance of Culex quinquefasciatus Say to chemical insecticides and the modification of the susceptibility of this mosquito to pyrethroid has stimulated studies on the activity of plants as alternative for its control. In this study, bioassays were carried out to verify the larvicidal activity of the oil-resin of Copaifera reticulata on C. quinquefasciatus. The bioassays were carried out with the oil dissolved in dimethylsulfoxide (DMSO), at the proportion of 0.4 ml of DMSO to 24.6 ml of distilled water. For each instar, the bioassays were carried out in plastic glasses with 100 ml solution using 20 larvae, wit four replications to adjust the lethal concentrations. The mortality observations were made after 48h exposure of the larvae to the solution. The control was carried out in distilled water and DMSO, with the same number of replications as the bioassays. The experiments were carried out in a biological chamber, controlled at 28 ± 1°C, 80 ± 5% relative humidity and 12h light. The larvae without movement were considered dead. The C. reticulata oil-resin demonstrated larvicide activity for all the C. quinquefasciatus instars. The LC50 found for the 1st, 2nd, 3rd and 4th larval instars were: 0.4, 0.9, 39 and 80 ppm, and the LC99 were 15, 15, 50 and 180 ppm, respectively.

Associação entre incidência de dengue, pluviosidade e densidade larvária de Aedes aegypti, no Estado de Goiás

INTRODUCTION: The larval density of Aedes aegypti fluctuates according to seasonal climatic changes. It rises in seasons with higher rainfall, according to the number of potential breeding sites available, thereby predisposing towards increased incidence of dengue. This study aimed to show the association between dengue cases, rainfall and the building infestation rate. METHODS: The municipalities were stratified according to the risk and transmission of dengue, and according to presence or absence of mosquito infestation. We used the building larval infestation rate as an indicator for the risk of transmission. RESULTS: There was a positive correlation between the building infestation rate, number of dengue cases and rainfall. Disease transmission was greater during the first four months of each year studied (period of high rainfall) and lower between June and September (season with low rainfall). Dengue cases occurred continually and in increased numbers between January and March of each year, and then declined in the months of April and May, when it ceased in most municipalities. The metropolitan region of Goiânia was responsible for more than 80% of the dengue cases in Goias. Transmission was continuous throughout the year, although lower during the period from May to December. Over the last three months, there was increased transmission, but usually still at low rates. CONCLUSIONS: The positive correlation between the building infestation rate and rainfall, and between this rate and the incidence of cases, indicated a significant association between increasing transmission and increasing numbers of dengue cases.

Larvicidal activity of oil-resin fractions from the Brazilian medicinal plant Copaifera reticulata Ducke (Leguminosae-Caesalpinoideae) against Aedes aegypti (Diptera, Culicidae)

Oil-resin fractions from Copaifera reticulata Ducke (Leguminosae-Caesalpinoideae) were evaluated for larvicidal activity on third larval instars of Aedes aegypti, in searching for alternative control methods for this mosquito. The bioactive fractions were chemically monitored by thin-layer chromatography, (1)H and 13C nuclear magnetic resonance and mass spectrometry. Bioassays were performed using five repetitions, at a temperature of 28+/-1 degrees C, relative humidity of 80+/- 5% and light and dark cycles of 12h. Mortality was indicated by darkening of the cephalic capsule after 24h of exposure of the larvae to the solutions. The most active fractions were CRM1-4 (sesquiterpenes) and CRM5-7 (labdane diterpenes), which showed LC50 values of 0.2 and 0.8 ppm, respectively.

Larvicidal effects of fungal Meroterpenoids in the control of Aedes aegypti L., the main vector of dengue and Yellow fever.

The mosquito Aedes aegypti is an increasing problem of public health, being the vector responsible for dengue and Yellow Fever in tropical and subtropical regions. The aim of this work was to determine the potential larvicidal activity of a series of meroterpenoids, compounds 1–7, previously obtained fungal secondary metabolites from Penicillium sp., against the third‐instar larvae of A. aegypti. The lethal concentrations (LC50 and LC90) of 1–7 were evaluated 24 h after exposure. Dehydroaustin (4) was the most active meroterpenoid in the series, with an LC50 value of 2.9 ppm, making it an attractive natural insecticide.

Alterações ultraestruturais em larvas de Aedes aegypti submetidas ao diterpeno labdano, isolado de Copaifera reticulata (Leguminosae), e à uma fração rica em taninos de Magonia pubescens (Sapindaceae)

INTRODUCTION: Dengue is an important public health problem in many countries and its main vector Aedes aegypti, is the mosquito most adapted to urban areas. For the first time, the mechanism of action of labdane diterpenoid extracted from Copaifera reticulata and the fraction enriched of catechin tannins extracted from Magonia pubescens is demonstrated through ultrastructural alterations of Aedes aegypti larvae. METHODS: Experiments were performed using a 0.9ppm solution of diterpenoid and 3.7ppm of the fraction as the main catechin tannin of molecular mass 846Da. The compounds were obtained by thin layer chromatography and identified by nuclear magnetic resonance of hydrogen and mass spectrometry. Larvae that achieved lethargic state were collected and dissected. Next, they were contrasted with 1% uranyl acetate, dehydrated, embedded and polymerized. Ultrathin sections were made, mixed with 3% uranyl acetate and lead citrate and placed in an electron microscope. RESULTS: The main ultrastructural alterations caused by the diterpenoid and by tanins in larvae of Aedes aegypti were: cytoplasmic vacuolation, alteration of microvilli, cellular aging, cell disruption and degeneration, formation of secretion vesicles and structural changes in microvilli, irregular nuclei and displacement of cells in the basal lamina. CONCLUSIONS: The fraction containing tannins and the diterpenoid caused the death of Aedes aegypti larvae by cell destruction in the midgut.