Among the pests that attack stored maize and wheat grain, Sitophilus oryzae (L.) and S. zeamais Motsch (Coleoptera: Curculionidae) are the most destructive. This paper is aimed at the study of the insecticidal effect and the residual action of organophosphate fenitrothion, pyrethroid esfenvalerate, and the mixture of both on S. oryzae and S. zeamais in stored maize and wheat. Grains were treated in order to obtain theoretical concentrations of 10 and/or 0.5 mg·kg −1 fenitrothion and esfenvalerate, respectively. The effectiveness experiments were installed as of 15, and 30 days, and subsequently at monthly intervals as of 12 months after grain treatment, or until mortality ceased in the plots. After mortality evaluation happened all individuals were eliminated, either dead or alive, and grains were kept for 60 days to assess the number of emerged progeny. The comparison of mortality curves of the pest species within each combination of grain type and insecticide showed significant differences. In general, the mortality of S. oryzae decreased faster than that of S. zeamais considering the grain type-insecticide combination. Esfenvalerate was ineffective in all combinations. Higher mortality of both species was observed on wheat grains treated with fenitrothion and fenitrothion + esfenvalerate mixture. Best results as to progeny control were obtained with fenitrothion and fenitrothion + esfenvalerate mixture. The factors that influenced the pest control are discussed in the present work.

-Insect-pest mobility can infl uence insect susceptibility to the insecticides used to control them. The objective of this work was to evaluate the fl ight activity of Sitophilus oryzae (L) and Sitophilus zeamais Motsch populations reared on corn and wheat grains, and its relationship with insecticide susceptibility. Unsexed adult insects with ages between 10 and 20 days were placed on a plastic tray. A 40-watt incandescent light bulb was positioned at a 50 cm height relative to the tray. Flight activity was evaluated during 30 min. In the LC 50 estimation bioassays, the insects were exposed to dry residues of the organophosphorus insecticide fenitrothion and of the pyrethroid insecticide esfenvalerate on the internal surface of glass vials. Mortality was evaluated 24h after installation of the experiments. Sitophilus zeamais showed greater fl ight activity when compared with S. oryzae; likewise, insects reared on corn had greater fl ight activity than those reared on wheat. Sitophilus oryzae was less susceptible to the insecticides studied than S. zeamais. Adults reared on wheat were more susceptible to the insecticides than those reared on corn. This study demonstrates that the lower fl ight activity of S. oryzae is related to its greater tolerance to insecticides.

In stored grains, smaller depositions and great variations with regard to theoretical insecticide doses are frequently found. The objective of this work was to evaluate the influence of the emulsifiable concentrate formulation on the physical properties of the liquid, volumetric distribution, droplet spectrum, and insecticide deposits on stored grains. To determine its physical properties, the applied mix was prepared at a concentration of 0.4% of commercial product. Volumetric distribution was used as an evaluation parameter in a model TJ-60 8002EVS hydraulic nozzle study, and clean water and insecticidal mix were used as test fluids. After the effective swath width (esw) had been determined for both fluids, an application system was built to apply theoretical concentrations of 10 and 0.5 mg kg-1 of fenitrothion and esfenvalerate, respectively. Mix viscosity was 82% higher than water viscosity; conversely, surface tension in the mix corresponded to 49% of the water surface tension value. For water and mix, esw values were 0.425 and 0.60 m, respectively. Deposits of both insecticides at the 0.60 m esw were significantly higher (P<0.05) than deposits at the 0.425 m esw. The results obtained demonstrate the great influence of emulsifiable concentrate formulation on the physical properties of the fluid, spray characteristics, and insecticide deposits on stored grains.

We developed a system to evaluate the performance of hydraulic nozzles used in stored corn and wheat grain protection experiments. An insecticidal mix was used as test fluid to determine the transversal volumetric distribution and droplets spectrum of a model TJ-60 8002EVS hydraulic nozzle. A mobile application system was built to apply a rate equivalent to 5 L t -1 and obtain theoretical concentrations of 10 and 0.5 mg kg -1 of fenitrothion and esfenvalerate, respectively. The corn and wheat grains were spread out as a fine layer. Three glass slides (0.1 × 0.05 m) were placed on the top surface of the grains to ensure that the intended application rate was achieved. After treatment, the deposits on both matrices were analyzed by gas chromatography. The fenitrothion deposit was higher than esfenvalerate, and the deposit on wheat was higher than on corn grains (P < 0.05). The deposits on the glass slides reached values of 100 and 93% of the intended theoretical fenitrothion and esfenvalerate concentrations, respectively. Deposits on the grains were lower than on the glass slides, with values of 64 and 52% of the intended theoretical fenitrothion and esfenvalerate concentrations, respectively. The results obtained demonstrate a high effectiveness of the method for evaluation of the performance of hydraulic nozzles when an insecticidal mix is used as test fluid. The factors that influenced insecticide deposition on glass slides and on grains are discussed in the present work. Key words: application technology, gas chromatography, insecticide deposits, corn, wheat SISTEMA PARA AVALIAR O DESEMPENHO DE BICOS HIDRÁULICOS UTILIZADOS EM EXPERIMENTOS DE PROTEÇÃO DE GRÃOS ARMAZENADOSRESUMO: A tecnologia de aplicação na proteção de grãos armazenados é de fundamental importância para melhorar a uniformidade de distribuição dos agrotóxicos na massa de grãos. Foi desenvolvido um sistema para avaliar o desempenho de bico hidráulico utilizado em experimentos de proteção de grãos de milho e trigo armazenados. Para determinar a distribuição volumétrica transversal e o espectro de gotas do bico hidráulico modelo TJ-60 8002EVS, utilizou-se calda inseticida como líquido teste. Um sistema móvel de aplicação foi construído para aplicar uma taxa equivalente a 5 L t -1 e obter uma concentração teórica de 10 e 0,5 mg kg -1 de fenitrotion e esfenvalerato, respectivamente. Os grãos foram espalhados em fina camada para o tratamento. Lâminas de vidro foram colocadas sobre a massa de grãos para certificar a aplicação da dose pretendida. Os depósitos em ambas matrizes foram analisados por técnica de cromatografia gasosa. O depósito de fenitrotion foi superior ao do esfenvalerato e o depósito nos grãos de trigo foi superior a do milho. Nas lâminas de vidro os depósitos atingiram valores de 100 e 93% da concentração teórica pretendida de fenitrotion e esfenvalerato, respectivamente. Nos grãos os depósitos foram inferiores aos das lâminas de vidro, com valores de 64 e 52% da concentração teórica pretendida de fenitrotion e esfenvalerato,...

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