Life stages, biological aspects and geographic distribution of Platyscytus decempunctatus (Heteroptera: Miridae: Phylinae)

Platyscytus decempunctatus is a small phytophagous mirid found only on Solanum cernuun (Solanaceae) plants. This species is characterized by the presence of two black marks on second anntenal segment and by dorsal spots on body. The authors present a taxonomic review of P. decempunctatus, with descriptions and illustrations of all stages, from egg to adult. Information about behavior and geographical distribution of the species are also presented.Platyscytus decempunctatus é um pequeno mirídeo fitófago encontrado somente em plantas de Solanum cernuun (Solanaceae). A espécie é caracterizada pela presença de duas máculas pretas no segundo segmento antenal e também por manchas dorsais no corpo. Os autores apresentam uma revisão de P. decempunctatus, com descrições e ilustrações de todos os estágios, de ovo a adulto. Informações sobre o comportamento e distribuição geográfica também são apresentadas

Factors affecting the attack rate of Bemisia tabaci on cucumber

O objetivo deste trabalho foi determinar os efeitos de pluviosidade, temperatura, predadores, parasitóides, idade de planta, composição química foliar, níveis de nitrogênio e potássio foliares, assim como de densidade de tricomas, na intensidade de ataque de Bemisia tabaci biótipo B em Cucumis sativus. Observaram-se maiores números de adultos e de ninfas de mosca-branca por folha com o aumento de idade de plantas. Adultos por folha e ovos cm-2 foram encontrados com maior freqüência na parte apical do que na parte mediana e basal do dossel das plantas. Entretanto, observou-se maior número de ninfas desse inseto no terço mediano do que nos terços apical e basal. Nitrogênio foliar afetou negativamente ninfas de mosca-branca. Pentacosano e octacosano afetaram positivamente adultos e o primeiro composto afetou também as ninfas dessa praga.The objective of this work was to determine the effects of rainfall, temperature, predators, parasitoids, plant age, leaf chemical composition, levels of leaf nitrogen and potassium, besides density of leaf trichomes, on attack intensity of Bemisia tabaci biotype B on the Cucumis sativus. An increase in the number of whitefly adults and nymphs per leaf was observed with plant aging. A higher number of whitefly adults per leaf and eggs cm-2 was verified in the apical part than in the middle and bottom part of the plants canopy. However, the higher number of whitefly nymphs was observed in the mid-part than in the apical and bottom part of the plant canopy. The incidence of whitefly nymphs was negatively affected with foliar nitrogen. Pentacosane and octacosane positively affected whitefly adults and the first compound also affected the nymphs of this pest species

Insecticide resistance and control failure likelihood among populations of the boll weevil (Anthonomus grandis) from Mato Grosso (Brazil)

The cotton producers from southern Mato Grosso are currently experiencing control failure with the use of the use of insecticides against the cotton boll weevil Anthonomus grandis Boheman, the main pest species of this commodity. Therefore, the present study was designed to survey insecticide resistance and the associated likelihood of control failure among boll weevil populations in the region. Ten insect populations were sampled during the 2016/2017 season and subjected to time-mortality (contact) bioassays in glass vials impregnated with dried insecticide residues at their respective label rates. The three insecticides most frequently used in the region were surveyed: the organophosphate malathion and the pyrethroids beta-cyfluthrin and zeta-cypermethrin. The survival curves showed estimates of the respective median survival time (LT50) for each combination of insecticide and insect copulation. However, there were no significant differences in susceptibility among populations. The estimates of control failure likelihood for each compound at their respective label rates also indicated negligible risk of control failure with their use. These findings are consistent with time-mortality results indicating the lack of insecticide resistant populations at the surveyed sampling sites, suggesting that the reported field control failures result from other causes such as problems with insecticide application

Diversidade genética estimada com marcadores ISSR em populações brasileiras de Zabrotes subfasciatus

The objective of this work was to evaluate the genetic diversity of populations of Zabrotes subfasciatus through ISSR molecular markers. Twelve populations from eight Brazilian states were sampled in the total of 269 individuals. Five ISSR primers were used and a total of 51 polymorphic bands were obtained. The percentage of polymorphism within population averaged 83.8%. Nei's unbiased expected heterozygosity ranged from 0.23 to 0.33, with an average of 0.29, and the Shannon & Weaver's index of gene diversity varied from 0.29 to 0.48, with an average of 0.42. At species level, these two indexes were 0.36 and 0.54, respectively. The analysis of molecular variance showed that 66% of the total molecular variance can be attributed to differences within population, while 34% was apportioned among populations. Mantel's test showed a low correlation between: geographic distance and genetic differentiation, genetic identity and genetic differentiation, and Nei's genetic distance and genetic differentiation. The genetic differentiation in Brazilian populations of Z. subfasciatus is low and geographic structuring is weak.O objetivo deste trabalho foi estimar a diversidade genética de populações de Zabrotes subfasciatus, por meio de marcadores moleculares ISSR. Foram avaliadas 12 populações, provenientes de oito estados brasileiros, no total de 269 indivíduos. Cinco iniciadores ISSR permitiram a obtenção do total de 51 fragmentos polimórficos. A percentagem média de locos polimórficos, dentro de cada população, foi de 83,8%. A heterozigosidade corrigida de Nei esperada variou de 0,23 a 0,33, com média de 0,29, e o índice de diversidade genética de Shannon e Weaver variou de 0,29 a 0,48, com média de 0,42. No nível de espécie, estes dois índices apresentaram valores de 0,36 e 0,54, respectivamente. A análise de variância molecular mostrou que 66% da variância molecular total pode ser atribuída a diferenças intrapopulacionais e que os 34% restantes podem ser atribuídos a diferenças interpopulacionais. O teste de Mantel mostrou baixa correlação entre: distância geográfica e diferenciação genética, identidade genética e diferenciação genética e, distância genética de Nei e diferenciação genética. As populações brasileiras de Z. subfasciatus possuem baixa diferenciação genética e fraca estruturação geográfica

Parasitism of the mite Acarophenax lacunatus on Tribolium castaneum

O objetivo deste trabalho foi avaliar o potencial de parasitismo do ácaro Acarophenax lacunatus (Cross & Krantz) sobre Tribolium castaneum (Herbst). As unidades experimentais consistiram de placas de Petri contendo 25 g de grãos de trigo infestados com 20 adultos desse coleóptero. Depois de sete dias da infestação, os ácaros foram introduzidos em diferentes densidades (0, 2, 4, 6, 8 e 10 fêmeas) nas placas de Petri. O aumento da densidade do ácaro acarretou aumento linear do parasitismo, com conseqüente redução das populações desse inseto. É possível utilizar esse ácaro no controle biológico de T. castaneum.The objective of this work was to assess the parasitism potential of Acarophenax lacunatus (Cross & Krantz) on Tribolium castaneum (Herbst). The experimental units encompassed Petri dishes containing 25 g of wheat infested with 20 adults of this beetle species. After seven days of infestation, different mite densities (0, 2, 4, 6, 8 and 10 females) were inoculated into the Petri dishes. The increase in mite density led to a linear increase in parasitism, and a consequent reduction in populations of this insect. It is possible to use this mite species in the biological control of T. castaneum

Sampling plan for B-biotype of Bemisia tabaci in cucumber crop

A adoção de programas de manejo integrado de pragas permite reduzir a aplicação de inseticidas e os planos convencionais de amostragem representam o ponto inicial na geração desses programas. Assim, o objetivo deste trabalho foi determinar plano de amostragem convencional para o biótipo B da mosca-branca Bemisia tabaci Genn. (Hemiptera: Aleyrodidae) na cultura do pepino. Foram avaliadas as densidades de ninfas e de adultos em dez lavouras comerciais de pepino, Tocantins, MG, estudando nove sistemas amostrais formados pela combinação de três técnicas (batida de folha em bandeja de plástico branco, contagem direta dos insetos na face inferior da folha e coleta de folha em sacola de plástico) e três unidades amostrais (folha do terço apical, mediano ou basal do espaldeiramento). A contagem direta em folha do terço basal foi o sistema com maior precisão econômica na amostragem de ninfas, mas não possibilitou a geração de plano de amostragem praticável. As batidas, em bandeja, de folha dos terços apicais, medianos ou basais do espaldeiramento foram os sistemas economicamente mais precisos na amostragem de adultos. Desses, apenas a batida de folha do terço mediano em bandeja gerou plano de amostragem praticável, sendo que este plano é composto de 196 amostras/lavoura.The adoption of pest management integrated programs decreases insecticide applications, and standardized sampling plans represent the initial point in the generation of those programs. This work aimed to determine a conventional sampling plan for B-biotype of the whitefly Bemisia tabaci Genn. (Hemiptera: Aleyrodidae) in cucumber crops. The densities of nymphs and adults were evaluated in ten commercial crops in Tocantins, Minas Gerais State, Brazil. Nine sampling systems compared three sampling techniques, which were the beating of leaf on white plastic trays, the direct counting of insects on abaxial leaf surface, and the leaf collection in plastic bag, and three sample units, a leaf on the apical, median, and basal thirds of the training system. The system with the largest economic precision in the nymphs sampling was the direct counting on leaf of the basal third of the training system. However, that system did not generate a practicable sampling plan. The systems with the largest economic precisions in the adults' sampling were the beating on plastic trays of a leaf from the apical, medium or basal portions of the training system. Only the sampling system of beating leaves of the third medium on plastic trays generated a practicable plan. The number of samples for the adults' sampling on the leaves of the medium portion of the training system was of 196 per field

Spatial distribution and losses by grain destroying insects in transgenic corn expressing the toxin Cry1Ab

Insect pests are one of the factors that most impact plant yield. The magnitude of the losses and the spatiotemporal pest distribution in crops is a result of their interactions with the environment. Therefore, the understanding of the causes of production losses and the pest spatial patterns is important for the development of suitable sampling plans and pest management programs. Thus, this study aimed to quantify grain losses caused by insects and to determine the spatial distribution pattern of arthropod pest species in Bt and non-Bt corn. The prevailing insect pests in the corn ears were the earworm and fall armyworm caterpillars (Helicoverpa spp. and Spodoptera frugiperda), the cornsilk fly (Euxesta spp.), the maize weevil (Sitophilus zeamais), and the square-necked grain beetle (Cathartus quadricollis). The non-Bt corn was more attacked by the caterpillars and the weevil, while Bt corn was more affected by the corn- silk fly Euxesta spp. Spatial dependence was significant for the damage caused by the caterpillars, the grain beetle and the maize weevil in both the Bt and non-Bt corn genotypes. The range of the damage caused by the insects was between 9.0–9.7 m for the caterpillars, 6.9– 12.20 m for the cornsilk fly, 10.7–80.4 m for the square-necked grain beetle, and 51.9–170.7 m for the maize weevil. The pattern of the spatial distribution of pest damage in both corn genotypes (i.e., Bt and non-Bt corn) was similar with a prevalence of moderate to strong spatial dependence and aggregate damage distribution. The plants near to the sampling points exhibited injury and infestation levels similar to those of the sampled plants