Genetic diversity, phylogenetic and phylogeographic analyses of Oncideres impluviata (Germar, 1823) (Coleoptera: Cerambycidae) in Rio Grande do Sul state, Brazil

ABSTRACT The Cerambycidae Oncideres impluviata (Germar, 1823) is an important insect pest for Acacia mearnsii De Wild in Southern Brazil. The damage caused by their girdling behavior reduces tree productivity, specially in the early years of plant establishment, when girdling is performed on the main trunk of trees. Here, we used a fragment of the mtDNA COI gene to analyze the genetic diversity, population structure and demography of O. impluviata in Southern Brazil, as well as to present the first hypothesis of phylogenetic relationships among species of the genus Oncideres. Our results identified five distinct haplotypes among the populations of O. impluviata, with the most common haplotype identified as O.imp_COI_01. The phylogenetic inferences corroborated the monophyly of O. impluviata with maximum statistical support. In addition, the phylogeny recovered three main population strains that are largely congruent with the haplotype network, which includes two lineages that are found in different edaphic regions of Rio Grande do Sul (Serra do Sudeste and Encosta Inferior do Nordeste). This is the first molecular phylogenetic assessment of O. impluviata. Our findings provide insights into the evolution of a significant species for the Brazilian forestry sector, as well as new resources for planning of pest management strategies.

Population analysis of white grubs (Coleoptera: Melolonthidae) throughout the Brazilian Pampa biome

ABSTRACT The replacement of natural grassland by cultivated areas might favor the increase in abundance of some root-feeding species such as the white grubs, which may become a constraint for field crop production. This research aimed to assay the population density and geographical distribution of white grubs pest and other species in natural grassland and cultivated areas throughout the Brazilian Pampa biome. White grubs were sampled in 18 locations in both landscape use types and identified. Population density (number of larvae m-2) was calculated for each recorded species and sorted within two groups (pest species and other species), compared between natural grasslands and cultivated areas, as well as among locations. A dendrogram to evaluate species similarity among locations was built based on combined data obtained from both landscape use types throughout the region. In total, 31 species were found in the Brazilian Pampa, and four of them are considered as crop pests: Diloboderus abderus (Sturm, 1826), Euetheola humilis (Burmeister, 1847), Lyogenys fusca (Blanchard, 1830), and Phyllophaga triticophaga Morón & Salvadori, 1998. The average population density of pest species in cultivated areas was less than five larvae m-2, at most of locations. Some species had a wide geographical distribution (e.g. D. abderus and Cyclocephala modesta Burmeister), while other melolontids occurred at only one location. The knowledge of which white grub species are present in a field and its population densities assist farmers to take proper management decisions.

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.

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.