Spatiotemporal Dynamics of Whitefly Bemisia tabaci (Hemiptera: Aleyrodidae) in Commercial Watermelon Crops.

Spatiotemporal dynamics studies of crop pests enable the determination of the colonization pattern and dispersion of these insects in the landscape. Geostatistics is an efficient tool for these studies: to determine the spatial distribution pattern of the pest in the crops and to make maps that represent this situation. Analysis of these maps across the development of plants can be used as a tool in precision agriculture programs. Watermelon, Citrullus lanatus (Thunb.) Matsum. and Nakai (Cucurbitales: Cucurbitaceae), is the second most consumed fruit in the world, and the whitefly Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is one of the most important pests of this crop. Thus, the objective of this work was to determine the spatiotemporal distribution of B. tabaci in commercial watermelon crops using geostatistics. For 2 yr, we monitored adult whitefly densities in eight watermelon crops in a tropical climate region. The location of the samples and other crops in the landscape was georeferenced. Experimental data were submitted to geostatistical analysis. The colonization of B. tabaci had two patterns. In the first, the colonization started at the outermost parts of the crop. In the second, the insects occupied the whole area of the crop since the beginning of cultivation. The maximum distance between sites of watermelon crops in which spatial dependence of B. tabaci densities was observed was 19.69 m. The adult B. tabaci densities in the eight watermelon fields were positively correlated with rainfall and relative humidity, whereas wind speed negatively affected whiteflies population.

Feasible sampling plan for Bemisia tabaci control decision-making in watermelon fields.

BACKGROUND: The silverleaf whitefly Bemisia tabaci is one of the most important pests of watermelon fields worldwide. Conventional sampling plans are the starting point for the generation of decision-making systems of integrated pest management programs. The aim of this study was to determine a conventional sampling plan for B. tabaci in watermelon fields. RESULTS: The optimal leaf for B. tabaci adult sampling was the 6th most apical leaf. Direct counting was the best pest sampling technique. Crop pest densities fitted the negative binomial distribution and had a common aggregation parameter (Kcommon ). The sampling plan consisted of evaluating 103 samples per plot. This sampling plan was conducted for 56 min, costing US$ 2.22 per sampling and with a 10% maximum evaluation error. CONCLUSIONS: The sampling plan determined in this study can be adopted by farmers because it enables the adequate evaluation of B. tabaci populations in watermelon fields (10% maximum evaluation error) and is a low-cost (US$ 2.22 per sampling), fast (56 min per sampling) and feasible (because it may be used in a standardized way throughout the crop cycle) technique. © 2017 Society of Chemical Industry.

Economic injury levels and sequential sampling plans for Frankliniella schultzei in watermelon crops.

BACKGROUND: The thrips Frankliniella schultzei is an important watermelon pest. Nevertheless, economic injury levels and sampling plans for this pest have not yet been determined for this crop. Thus, the objective of the present study was to determine the economic injury levels and develop sequential sampling plans for F. schultzei in conditions of low, medium and high fruit prices. RESULTS: The attack of F. schultzei on watermelon plants at the vegetative stage reduced the crop's productivity, which did not happen at the flowering and fruiting stage. The economic injury levels were 0.09, 0.04 and 0.02 thrips leaf-1 when the watermelon price was low ($US 62.5 t-1 ), medium ($US 140.63 t-1 ) and high ($US 218.75 t-1 ) respectively. The three sequential sampling plans for F. schultzei generated for the economic injury levels resulted in similar and more rapid decisions compared with the conventional plan, especially when the pest density was high. CONCLUSIONS: The three economic injury levels and the sequential sampling plans generated in the present study can be incorporated into integrated pest management programmes for watermelon crops because these plans provide a rapid and adequate control decision for F. schultzei. © 2016 Society of Chemical Industry.

Influência do fósforo na qualidade fisiológica de sementes de feijão comum armazenadas sob condições naturais / Phosphorus influence on physiological quality of common bean seeds stored under natural conditions

Com o objetivo de avaliar a influência do fósforo na qualidade fisiológica de sementes de feijão comum cultivado em solos de terras altas no Estado do Tocantins, realizou-se a pesquisa no Laboratório de Análise de Sementes da Universidade Federal do Tocantins - Campus Universitário de Gurupi com sementes de 19 genótipos de feijão comum cultivados em dois ambientes, um simulando condição de estresse de fósforo (20 kg ha-1) e o outro simulando condições ideais (120 kg ha-1). O delineamento experimental adotado foi a de blocos ao acaso, em esquema fatorial 19 x 2, sendo 19 genótipos e dois níveis de fósforo, com quatro repetições, sendo esses dados analisados por meio do teste Scott-Knott e Tukey, com 5% de probabilidade. A qualidade fisiológica das sementes de feijão comum foi realizada por meios dos testes padrão de germinação, primeira contagem, tetrazólio e massa de mil sementes. Entre os cultivares houve desempenho diferenciado quanto à qualidade fisiológica de sementes de feijão; para os cultivares IACGalante, IAC-Carioca Eté, IAC-Una, IPR-Juriti, IPR-Colibri, IPR-Siriri, IPR-139, IPR-Gralha, IPR-Tiziu, IPR-Chopim e IPR-Corujinha o incremento de fósforo não resultou em melhoria na qualidade fisiológica das sementes produzidas; e os genótipos IAC-Carioca Tybatã, IAC-Carioca Eté e Tangará produziram sementes de melhor qualidade fisiológica.

In order to evaluate the phosphorus influence over physiological quality of common bean seeds grown on upland soil in Estate of Tocantins, help research was carried out on the Seed Analysis Laboratory of Universidade Federal do Tocantins- Campus of Gurupi with seeds of Nineteen bean genotypes tested. They were grown in two environments, one simulating condition of phosphorus stress (20 kg ha-1) and another one simulating ideal conditions (120 kg ha-1). The experimental design adopted was the completely randomized blocs in a factorial scheme 19x2, being 19 genotypes and 2 levels of phosphorus, with four replications. The data was analyzed and applied the Scott-Knott and Tukey tests, both with 5% of probability. The physiological quality of common bean was analyzed through the standard germination test, first count, tetrazolium test and one thousand grains mass. Among the cultivars there was a differentiated physiological quality of bean seeds; for cultivars IAC-Galante, IAC-Carioca Eté, IAC-Una, IPR-Juriti, IPR-Colibri, IPRSiriri, IPR-139, IPR-Gralha, IPR-Tiziu, IPR-Chopim and IPR-Corujinha, the increases in the level of phosphorus did not result on better physiological quality of the produced seeds; and the genotypes IAC-Carioca Tybatã, IAC-Carioca Eté and Tangará produced seeds of better physiological quality.