Susceptibility of Aedes aegypti (L) to the insect growth regulators diflubenzuron and methoprene in Uberlândia, State of Minas Gerais

Aedes aegypti (L) (Diptera: Culicidae) was reared in several concentrations of diflubenzuron and methoprene under laboratory conditions in Uberlândia, State of Minas Gerais, southeastern Brazil. Characteristics such as LC50 and LC95, the susceptibility of immature stages of different ages to these insect growth regulators and their residual effects were studied. The LC50 and LC95 of diflubenzuron and methoprene were 5.19 and 12.24 ppb; 19.95 and 72.08 ppb, respectively. While diflubenzuron caused great mortality in all larval instars, methoprene was more effective when the mosquito was exposed from the start of the fourth larval instar onwards. Commercial concentrations of these two insect growth regulators close to LC95 presented greater residual activity than did their respective technical formulations. The parameters were compared with those obtained elsewhere. The characteristics investigated here indicate that these insect growth regulators are effective alternatives for controlling the dengue vector in the Uberlândia region.

Impact of insecticide resistance on the field control of Aedes aegypti in the State of São Paulo

IntroductionThe need to control dengue transmission by means of insecticides has led to the development of resistance to most of the products used worldwide against mosquitoes. In the State of São Paulo, the Superintendência de Controle de Endemias(SUCEN) has annually monitored the susceptibility of Aedes aegypti to insecticides since 1996; since 1999, surveys were conducted in collaboration with the National Network of Laboratories (MoReNAa Network) and were coordinated by the Ministry of Health. In this study, in addition to the biological characterization of insecticide resistance in the laboratory, the impact of resistance on field control was evaluated for vector populations that showed resistance in laboratory assays.MethodsField efficacy tests with larvicides and adulticides were performed over a 13-year period, using World Health Organization protocols.ResultsData from the field tests showed a reduction in the residual effect of temephos on populations with a resistance ratio of 3. For adults, field control was less effective in populations characterized as resistant in laboratory qualitative assays, and this was confirmed using qualitative assays and field evaluation.ConclusionsOur results indicated that management of resistance development needs to be adopted when insect populations show reduced susceptibility. The use of insecticides is a self-limiting tool that needs to be applied cautiously, and dengue control requires more sustainable strategies.

Vinhaça e adubos minerais(I)

In this paper it is studied the action of vinasse as compared to mineral fertilizers. Beans, corn, cotton and sesame were cultivated in randomized blocks receiving the following treatments: A = mineral fertilizers (N, P, K); V = vinasse at the rate of 1,000,000 liters per Ha; AV = mineral fertilizers + vinasse; T = control. Statistical analysis of the experiments has consistently revealed the superiority of vinasse either combined or not with the mineral fertilizers over the remaining treatments. There was no significant difference between V and AV which shows the surprizing role of vinasse when applied to light soils such as those employed in the present experiments. By employing 1,000,000 liters of vinasse to the hectare the following amounts of nutrientes were applied to the crops in this experiment: 470 Kg of nitrogen 50 Kg of P2O5 and 3,100 Kg of K2O corresponds to 3,133 Kg of Chilean nitrate/ha 250 Kg of superphosphate and 5,160 Kg of muriate of potash Hence one cannot say that the action of vinasse is of a purely physical nature. In our opinion its outstanding action is due to: 1st raise in the pH value of the soil; 2nd addition of a tremendous amount of plant nutrients; 3rd supplying organic matter in a very finely divided state with all its benefical effects in soil structure, water holding capacity, adsorption of nutrients to prevent leaching, etc. A rotation experiment is now being carried out to study the residual effect of vinasse.

Expression of mosquito active toxin genes by a Colombian native strain of the gram-negative bacterium Asticcacaulis excentricus

Mosquito control with biological insecticides, such as Bacillus sp. toxins, has been used widely in many countries. However, rapid sedimentation away from the mosquito larvae feeding zone causes a low residual effect. In order to overcome this problem, it has been proposed to clone the Bacillus toxin genes in aquatic bacteria which are able to live in the upper part of the water column. Two strains of Asticcacaulis excentricus were chosen to introduce the B. sphaericus binary toxin gene and B. thuringiensis subsp. medellin cry11Bb gene cloned in suitable vectors. In feeding experiments with these aquatic bacteria, it was shown that Culex quinquefasciatus, Aedes aegypti, and Anopheles albimanus larvae were able to survive on a diet based on this wild bacterium. A. excentricus recombinant strains were able to express both genes, but the recombinant strain expressing the B. sphaericus binary toxin was toxic to mosquito larvae. Crude protease A. excentricus extracts did not degrade the Cry11Bb toxin. The flotability studies indicated that the recombinant A. excentricus strains remained in the upper part of the water column longer than the wild type Bacillus strains.

Fipronil Insecticide: Novel Application against Triatomine Insect Vectors of Chagas Disease

We investigated the efficacy and the residual effect of fipronil® against two species of triatomine bugs, Triatoma infestans and Rhodnius neglectus, in laboratory conditions measuring concentration-response and residual activity on different surfaces (dried mud and lime coated mud). Lethal concentrations (LC50,90) were determined on filter paper. The higher insecticide efficacy against R. neglectus when compared to T. infestans may be partially attributed to the differences in their biological cycles and genetic structures. Comparison with lambdacyhalothrin wettable powder showed that fipronil mortality rates (above 50%) were observed on mud blocks and lime-coated mud blocks up to 3 months when fipronil was sprayed at 100 and 200 mg a.i./m². Residual effect deeply decayed after 3 months; and at 6 months post treatment mortality was not observed. In contrast, lambdacyhalothrin showed a long lasting residual effect on both surfaces up to 6 months. Also, it should be mentioned that fipronil had a slow, but lethal activity on the triatomine bugs when wettable formulations were used on porous surfaces.

The efficacy of a chitin synthesis inhibitor against field populations of organophosphate-resistant Aedes aegypti in Brazil

The mosquito Aedes aegypti is the main focus of dengue control campaigns. Because of widespread resistance against conventional chemical insecticides, chitin synthesis inhibitors (CSIs) are considered control alternatives. We evaluated the resistance status of four Brazilian Ae. aegypti populations to both the organophosphate temephos and the pyrethroid deltamethrin, which are used in Brazil to control larvae and adults, respectively. All vector populations exhibited high levels of temephos resistance and varying rates of alterations in their susceptibility to pyrethroids. The effect of the CSI novaluron on these populations was also investigated. Novaluron was effective against all populations under laboratory conditions. Field-simulated assays with partial water replacement were conducted to evaluate novaluron persistence. Bioassays were continued until an adult emergence inhibition of at least 70% was attained. We found a residual effect of eight weeks under indoor conditions and novaluron persisted for five-six weeks in assays conducted in an external area. Our data show that novaluron is effective against the Ae. aegypti populations tested, regardless of their resistance to conventional chemical insecticides.

Bioactivity of Indonesian mahogany, Toona sureni (Blume) (Meliaceae), against the red flour beetle, Tribolium castaneum (Coleoptera, Tenebrionidae)

Bioactivity of Indonesian mahogany, Toona sureni (Blume) (Meliaceae), against the red flour beetle, Tribolium castaneum (Coleoptera, Tenebrionidae). The insecticidal activity of Toona sureni (Blume) Merr. was evaluated considering repellency, mortality and progeny production of F1 adults of Tribolium castaneum (Herbst, 1797) (Coleoptera, Tenebrionidae). Dried extract of seeds of T. sureni was dissolved in acetone to prepare solution of various concentrations (0.5, 1.0, 2.5 and 5.0%). To test for repellency, the insects were exposed to treated filter paper. Mortality of larvae, pupae and adults was evaluated by the treatment of spraying the insects with different concentrations of T. sureni extract. Residual effect of the extract was also evaluated considering the production of progeny of F1 adults. The highest repellency (93.30%) of T. castaneum occurred at the highest concentration (5.0% suspension of T. sureni); while the lowest (0.0%) repellency occurred at 0.5% suspension after 1 day of treatment. The highest mortality against adults (86.71%), larvae (88.32%) and pupae (85%) occurred at 5% suspension at 8 days after application. There was a negative correlation between the concentrations of T. sureni and the production of F1 adult's progeny of T. castaneum. The highest number of progeny (147) of T. castaneum occurred in the control at 7 days after treatment; and the lowest number of progeny (43) occurred at 5.0% concentration in 1 day after treatment. The results show that T. sureni is toxic to T. castaneum and has the potential to control all stages of this insect in stored wheat.

Surface and subsurface decomposition of a desiccated grass pasture biomass related to erosion and its prediction with RUSLE

Erosion is deleterious because it reduces the soil's productivity capacity for growing crops and causes sedimentation and water pollution problems. Surface and buried crop residue, as well as live and dead plant roots, play an important role in erosion control. An efficient way to assess the effectiveness of such materials in erosion reduction is by means of decomposition constants as used within the Revised Universal Soil Loss Equation - RUSLE's prior-land-use subfactor - PLU. This was investigated using simulated rainfall on a 0.12 m m-1 slope, sandy loam Paleudult soil, at the Agriculture Experimental Station of the Federal University of Rio Grande do Sul, in Eldorado do Sul, State of Rio Grande do Sul, Brazil. The study area had been covered by native grass pasture for about fifteen years. By the middle of March 1996, the sod was mechanically mowed and the crop residue removed from the field. Late in April 1996, the sod was chemically desiccated with herbicide and, about one month later, the following treatments were established and evaluated for sod biomass decomposition and soil erosion, from June 1996 to May 1998, on duplicated 3.5 x 11.0 m erosion plots: (a) and (b) soil without tillage, with surface residue and dead roots; (c) soil without tillage, with dead roots only; (d) soil tilled conventionally every two-and-half months, with dead roots plus incorporated residue; and (e) soil tilled conventionally every six months, with dead roots plus incorporated residue. Simulated rainfall was applied with a rotating-boom rainfall simulator, at an intensity of 63.5 mm h-1 for 90 min, eight to nine times during the experimental period (about every two-and-half months). Surface and subsurface sod biomass amounts were measured before each rainfall test along with the erosion measurements of runoff rate, sediment concentration in runoff, soil loss rate, and total soil loss. Non-linear regression analysis was performed using an exponential and a power model. Surface sod biomass decomposition was better depicted by the exponential model, while subsurface sod biomass was by the power model. Subsurface sod biomass decomposed faster and more than surface sod biomass, with dead roots in untilled soil without residue on the surface decomposing more than dead roots in untilled soil with surface residue. Tillage type and frequency did not appreciably influence subsurface sod biomass decomposition. Soil loss rates increased greatly with both surface sod biomass decomposition and decomposition of subsurface sod biomass in the conventionally tilled soil, but they were minimally affected by subsurface sod biomass decomposition in the untilled soil. Runoff rates were little affected by the studied treatments. Dead roots plus incorporated residues were effective in reducing erosion in the conventionally tilled soil, while consolidation of the soil surface was important in no-till. The residual effect of the turned soil on erosion diminished gradually with time and ceased after two years.

Sewage sludge as nitrogen and phosphorus source for cane-plant and first ratoon crops

The use of sewage sludge in Brazilian agriculture was regulated by the resolution no. 375 Conama, in 2006. However, there is a lack of research to adequate the mineral N and P fertilizer doses to be applied in agricultural fields treated with this residue. In a field experiment, the effects of application rates of sewage sludge and mineral N and P fertilizers on the productivity and technical characteristics of the cane-plant and first ratoon (residual effect) crops were evaluated. Four doses of sewage sludge (0, 3.6, 7.2 and 10.8 t ha-1, dry base), of N (0, 30, 60 and 90 kg ha-1) and of P2O5 (0, 60, 120 and 180 kg ha-1) were combined in a factorial and laid out on randomized block design, a with two replications. To evaluate the residual effect of the sludge, 120 kg ha-1 N and 140 kg ha-1 of K2O were applied in all plots. Sludge application at cane planting, with or without N and/or P fertilizer increased the stalk yield from 84 up to 118 t ha-1, with no alteration in the sugarcane quality, compared with the application of NPK fertilizer alone, resulting in a stalk yield of 91 t ha-1. The study of the response surface for stalk yield on lowfertility soil was the basis for a recommendation of mineral N and P fertilizer doses for sugarcane implantation as related to sewage sludge application rates. It was also concluded that a sludge application of 10.8 t ha-1, which is the sludge dose established based on the N criterion according to the resolution Conama nº 375, could a) reduce the use of mineral N by 100 % and of P2O5 by 30 %, with increments of 22 % in stalk yield, as a direct effect of sludge application to cane plant crop, and b) increase the stalk yield in the second harvest (first ratoon) by up to 12 % and sugar yield by up to 11 %, by the residual effect of sludge application to sugar cane.

Ammonium chloride as nitrogen source in sugarcane harvested without burning

The great difficulty of incorporation of N fertilizers into the "green sugarcane" system causes concern and since urea is the most commonly used source, there is the risk of loosing NH3 through volatilization. For this reason, a field experiment was undertaken (in a Hapludox Typic) with the objective of evaluating the agronomic efficiency of ammonium chloride on stubble of the second ratoon (SP89 1115), as well as its residual effect on the subsequent cycle (third ratoon). The experimental design was randomized blocks with four replications. Treatments consisted of three N rates (60, 120 and 180 kg ha-1 N) in the form of NH4Cl, in addition to a control treatment without the addition of N fertilizer. The ratoon cane of the second cutting was harvested in November 2006 and the treatments were applied in December 2006. The second ratoon was harvested mechanically in November 2007 and in December 2007, 450 kg ha-1 of the NPK mixture 20-05-19 was applied, providing 90, 22 and 86 kg ha-1 N, P2O5 and K2O, respectively, for the purpose of evaluating the effect of residual-N from the treatments implanted in December 2006. An increase in the rates of N-NH4Cl had a positive effect on the leaf concentrations of P, Mg and S. Stalk yield (MSS - Mg ha-1 of sugarcane stalks) and sugar (MSH - Mg ha-1 of sucrose) in the November 2006 harvest responded linearly to the increase of N doses in the form of NH4Cl. In relation to the effect of residual-N in the 2007/2008 harvest, it was observed, in general, that the concentrations of macronutrients in the sugarcane leaf +1 were within the range considered adequate in the state of São Paulo, Brazil. The residual-N of the NH4Cl doses resulted in a significant reduction in stalk (MSS) and sugar (MSH) production. It may be concluded that the NH4Cl source at a dose of 120 kg ha-1 N in ratoon fertilization of the second cutting was agronomically efficient, presenting, however, less efficiency of residual-N in the subsequent cycle.

Recovery of degraded pasture in Rondônia: macronutrients and productivity of brachiaria brizantha

Pasture is the main form of land use in Amazonia. Over time the pasture grass loses vigor and yields decrease, indicating a certain degree of degeneration. The main causes of degradation are lack of pasture maintenance and subsequent weed infestation, the choice of regionally unsuitable forage species and excessive grazing. The main purpose of this study was to evaluate the impact of different recovery managements on soil chemical properties and grass yield of a degraded pasture in Rondônia. For this purpose, an experiment was installed in October 2001, consisting of five treatments: C = control; HA = harrowing + NPK + micronutrients; HE = Herbicide + NK + micronutrients; R = No-tillage rice + NPK + micronutrients; and S = No-tillage soybean + PK + micronutrients. The following N, P and K sources were used: ammonium sulfate for N, calcined phosphate for P and potassium chloride for K. The experiment was arranged in a randomized block design with four replications. The shoot dry matter yield of the grass was analyzed as of the 35th month of experimentation, in a dry and a rainy period. Phosphorus fertilization resulted in significant increases in Ca2+ and Mg2+ and increasing trend of P in the topsoil in the initial months of the experiment in treatments HA and S and increases in Ca2+ and P (trend) in the treatment R. The cumulative production of Brachiaria brizantha, from Sep/2004 to Mar/2005, was 30,025, 28,267 and 27,735 kg ha-1 shoot dry matter in the treatments HA, R and S, respectively. These values differed significantly from treatments C and HE, with 17,040 and 17,057 kg ha-1, respectively. It was concluded that phosphorus fertilization associated to pasture reform was effective to raise the dry matter yield of Brachiaria brizantha. Rice or soybean under no-tillage is recommended as a practice of pasture recovery, due to the residual effect of fertilization.

Application of alkaline waste from pulp industry to acid soil with pine

In Brazil extensive areas are covered with pine forests, planted for pulp and paper production. This industry generates solid alkaline waste, such as dregs. The application of this dregs to forest soils is an alternative for soil acidity correction and plant nutrient supply, as well as a solution for its proper disposal. The purpose of this study was to compare the residual effect of surface application of dregs and dolomitic lime on (a) changes in the physical and chemical properties of an acidic soil and (b) pine tree development. The experiment was carried out in 2004 in Bocaina do Sul, Santa Catarina, consisting of the application of increasing dreg and lime rates to a Pinus taeda L. production area, on a Humic Cambisol, in a randomized block design with four replications and 10 x 10 m plots. The treatments consisted of levels of soil acidity amendments corresponding to the recommendations by the SMP method to reach pH 5.5 in the 0-20 cm layer, as follows: no soil amendment; dregs at 5.08 (1/4 SMP), 10.15 (1/2 SMP) and 20.3 Mg ha-1 (1 SMP); and lime at 8.35 (1/2 SMP) and 16.7 Mg ha-1 (1 SMP). Soil layers were sampled in 2010 for analyses of soil chemical and physical properties. The diameter at breast height of the 6.5 year old pine trees was also evaluated. Surface application of dregs improved soil chemical fertility by reducing acidity and increasing base saturation, similar to liming, especially in surface layers. Dregs, comparable to lime, reduced the degree of clay flocculation, but did not affect the soil physical quality. There was no effect of the amendments on increase in pine tree diameter. Thus, the alternative to raise the pH in forest soils to 5.5 with dregs is promising for the forestry sector with a view to dispose of the waste and increase soil fertility.

Silicate fertilization of tropical soils: silicon availability and recovery index of sugarcane

Sugarcane is considered a Si-accumulating plant, but in Brazil, where several soil types are used for cultivation, there is little information about silicon (Si) fertilization. The objectives of this study were to evaluate the silicon availability, uptake and recovery index of Si from the applied silicate on tropical soils with and without silicate fertilization, in three crops. The experiments in pots (100 L) were performed with specific Si rates (0, 185, 370 and 555 kg ha-1 Si), three soils (Quartzipsamment-Q, 6 % clay; Rhodic Hapludox-RH, 22 % clay; and Rhodic Acrudox-RA, 68 % clay), with four replications. The silicon source was Ca-Mg silicate. The same Ca and Mg quantities were applied to all pots, with lime and/or MgCl2, when necessary. Sugarcane was harvested in the plant cane and first- and second-ratoon crops. The silicon rates increased soil Si availability and Si uptake by sugarcane and had a strong residual effect. The contents of soluble Si were reduced by harvesting and increased with silicate application in the following decreasing order: Q>RH>RA. The silicate rates promoted an increase in soluble Si-acetic acid at harvest for all crops and in all soils, except RA. The amounts of Si-CaCl2 were not influenced by silicate in the ratoon crops. The plant Si uptake increased according to the Si rates and was highest in RA at all harvests. The recovery index of applied Si (RI) of sugarcane increased over time, and was highest in RA.

Crop response to organic fertilization with supplementary mineral nitrogen

Animal manure is applied to the soil as a nutrient source, especially of nitrogen, to plants. However, manure application rates can be reduced with the use of N fertilizer in topdressing. The aim of this study was to evaluate crop responses to different application rates of animal manure sources, used alone and supplemented with mineral N topdressing, in a no-tillage system. The study was carried out from 2005 to 2008 on a Hapludalf soil. The treatments consisted of rates of 10, 20 and 30 m³ ha-1 of pig slurry (PS), and of 1 and 2 t ha-1 of turkey manure (TM), applied alone and supplemented with topdressed N fertilizer (TNF), as well as two controls, mineral fertilization (NPK) and one control without fertilizer application. Grain yield in common bean and maize, and dry matter yield and nutrient accumulation in common bean, maize and black oat crops were evaluated. Nitrogen application in topdressing in maize and common bean, especially when PS was used at rates of 20 and 30 m³ ha-1, and TM, at 2 t ha-1, proved effective in increasing the crop grain yields, showing the viability of the combined use of organic and industrialized mineral sources. Nitrogen accumulation in maize and common bean tissues was the indicator most strongly related to grain yield, in contrast with the apparent nutrient recovery, which was not related to the N, P and K quantities applied in the organic sources. No clear residual effect of N topdressing of maize and common bean was observed on the dry matter yield of black oat grown in succession to the main crops with PS and TM applications.

Boron Leaching Decreases withIncreases on Soil pH

ABSTRACT Management of boron fertilization depends on the magnitude of B leaching in the soil profile, which varies proportionally with the concentration of B in the soil solution, which, in turn, decreases as the soil pH increases due to the higher sorption of B on soil solid surfaces. The objective of this study was to quantify the effect of liming and rates of B applied to the soil on B leaching. The experiment was carried out in the laboratory in 2012, and treatments consisted of a factorial combination of two rates of liming (without and with lime to raise the soil pH to 6.0) and five rates of B (0, 10, 20, 50 and 100 mg kg-1, as boric acid). A Typic Rhodudalf was used, containing 790 g kg-1 clay and 23 g kg-1 organic matter; the pH(H2O) was 4.6. Experimental units were composed of PVC leaching columns (0.10 m in diameter) containing 1.42 kg of soil (dry base). Boron was manually mixed with the top 0.15 m of the soil. After that, every seven days for 15 weeks, 300 mL of distilled water were added to the top of each column. In the percolated solution, both the volume and concentration of B were measured. Leaching of B decreased with increased soil pH and, averaged across the B rates applied, was 58 % higher from unlimed (pH 4.6) than from limed (pH 6.6) samples as a result of the increase in B sorption with higher soil pH. In spite of its high vertical mobility, the residual effect of B was high in this oxisol, mainly in the limed samples where 80 % of B applied at the two highest rates remained in the soil, even after 15 water percolations. Total recovery of applied B, including leached B plus B extracted from the soil after all percolations, was less than 50 %, showing that not all sorbed B was quantified by the hot water extraction method.