Density and growth rates of spider mites in relation to phenological stages of soybean cultivars in Brazil.

The population fluctuations of spider mites on different soybean cultivars were studied in two experiments performed in the municipalities of São Sepé (experiment 1) and Santa Maria (experiment 2) in the state of Rio Grande do Sul, Brazil. The number of cultivars was 20 in São Sepé and 25 in Santa Maria, and at each location leaves were sampled from 15 plants per cultivar every week throughout the entire plant developmental cycle, amounting to 11 and 10 samplings in experiment 1 and 2, respectively. The statistical analysis revealed that mite densities varied significantly with cultivar and time. Besides, the interaction between soybean cultivars and sampling times was significant at both locations. This indicates that the populations did not vary in the same way among cultivars over time, which is attributed to differences among the cultivars with respect to their phenology and response to spider mites. Equations for describing the mite population dynamics were estimated for each cultivar, mostly by fitting cubic equations to the weekly growth rates (per capita changes) in mite densities. We also found that the highest growth rates for mites on soybean cultivars in both locations occurred after the beginning of flowering, when the plants shifted from the vegetative to reproductive stages, about 3 weeks before reaching the peak densities.

A sampling procedure for quantifying mites in soybeans.

To control phytophagous mites on soybean crops in an economically viable way, it is necessary to quantify the occurrence of the mites on the leaflets. Estimating the number of mites cm(-2) on leaflets is more difficult because of their irregular distribution on the leaflet surface. Therefore, the aim of this study was to determine the count-area/leaflet and the number of soybean leaflets to quantify the mites. One hundred infested plants were randomly collected. One leaflet was removed from each plant and divided into 32 sections (1.0 cm(2) per section), arranged in four columns and eight rows, to count the mites (adults, nymphs and eggs). The ideal count-area size per leaflet (Xo) was estimated by the maximum curvature of the coefficient of variation method for each of the 100 leaflets. For a count-area of Xo size, we obtained the number of mites cm(-2) per leaflet and, using the bootstrap resampling method, we estimated the point and interval averages as well as the sample size for a pre-established error. We suggest that the determination of the evaluated area size on each soybean leaflet (20 cm(2) in this case) and the bootstrap resampling estimate of the appropriate number of leaflets (12 in this case) for a bootstrap confidence interval of four mites (adults + nymphs) cm(-2) is sufficient to standardize the sampling-procedures for quantifying mites on soybean leaflets.

Application methods and insecticides for controlling stink bugs in soybean / Métodos de aplicação e inseticidas no controle de percevejos na cultura da soja

Insecticides application is the most widely used form to control stink bugs in soybean, being the application technology and the insecticide used the major factors for an efficient control. The experiment was conducted in a soybean field during the 2008/09 growing season, in São Sepé, RS, in order to evaluate efficiency of three methods of application and two insecticides for controlling stink bugs in soybeans. The experimental design used was completely randomized, in a factorial scheme 3x2 +1 control, with five replicates. The experimental units had dimensions of 40.0 x 40.0 m. The factor A was represented by the methods of application, as follows: A1- Tractorized spray with hydraulic nozzle; A2- Aerial, with rotary disc atomizers and A3- Aerial, with hydraulic nozzles. The factor B was represented by the insecticides, as follows: B1- thiamethoxam + lambda-cyhalothrin and B2-acephate. Ground and aerial applications with low volume oily had greater efficiency for controlling stink bugs in soybean, where led to an increase in soybean grain yield. Insecticides thiamethoxam + lambda-cyhalothrin and acephate were similar in controlling stink bugs and in residual effect.

A aplicação de inseticidas é a forma mais utilizada no controle de percevejos na cultura da soja, sendo a escolha da tecnologia de aplicação e do inseticida fundamental para obtenção de um controle eficiente. O experimento foi desenvolvido em lavoura comercial de soja, na safra agrícola 2008/09, em São Sepé, RS, com o objetivo de avaliar a eficiência de três métodos de aplicação e dois inseticidas no controle de percevejos na soja. O delineamento experimental utilizado foi inteiramente casualizado, em esquema fatorial 3x2+1 testemunha, com cinco repetições. As unidades experimentais tiveram dimensões de 40,0 x 40,0 m. O fator A foi representado pelos métodos de aplicação, sendo: A1- Terrestre com pontas hidráulicas, A2- Aérea, com atomizadores rotativos de discos e A3- Aérea, com pontas hidráulicas. O fator B foi representado pelos inseticidas sendo: B1- tiametoxam + lambda-cialotrina e B2- acefato. As aplicações terrestres e aéreas com baixo volume oleoso apresentam maior eficiência no controle de percevejos na cultura da soja, refletindo-se este controle em maior rendimento de grãos. Os inseticidas tiametoxam + lambda-cialotrina e acefato apresentam controle de percevejos e efeito residual semelhante.

Aspectos biológicos da fase adulta dos curculionídeos-das-raízes dos citros / Biological aspects of the adult phase of citrus root weevils

O objetivo deste trabalho foi estudar alguns parâmetros biológicos da fase adulta de duas espécies de curculionídeos-das-raízes dos citros. Os insetos foram coletados em citros em Itapetininga, SP, levados ao Laboratório de Biologia de Insetos da ESALQ/USP, em Piracicaba, SP, onde foram mantidas as espécies Naupactus cervinus Boheman e Naupactus versatilis Hustache. Foi avaliada a longevidade, o tempo de alimentação, o período de pré-oviposição, a oviposição, o número de posturas e de ovos, além do consumo de folhas de citros. As espécies de curculionídeos-das-raízes dos citros apresentaram diferenças nas características biológicas e no potencial de danificar os citros. N. versatilis é potencialmente mais prejudicial aos citros, pois coloca um número maior de ovos (214,6 x 120,9 ovos), apresenta maior longevidade (30,9 x 25,2 dias) e consome maior área foliar (31,0 x 15,0cm²).

This work research was aimed at studing some characteristics of the adult phase of two species of citrus root weevils. Naupactus cervinus Boheman, Naupactus versatilis Hustache were collected from citrus in Itapetininga, SP, and taken to the Insect Biology Laboratory of ESALQ/USP, in Piracicaba, SP. Longevity, feeding time, pre-oviposition period, oviposition, number of egg-laying and eggs, and the consumption of the citrus leaf during the adult phase were evaluated. N. versatilis is potentially more dangerous to citrus, because it lays a larger number of eggs (214.6 x 120.9 eggs), has a higher longevity (30.9 x 25.2 days) and consumes a larger leaf area (31.0 x 15.0cm²).