Biological activity and persistence of pirimiphos-methyl applied to maize grain at different temperatures

Abstract

The expansion of dryeration may impose a further problem for insect control with protectants -the high grain temperatures during insecticide spraying. To assess the impact of this procedure on insecticide activity, maize grains at different temperatures (25, 30, 35, 40 and 45°C) were sprayed with pirimiphos-methyl. Residue analyses were carried out every 30 days and insecticide biological activity towards Sitophilus zeamais and Tribolium castaneum was assessed every 15 days throughout the experimental period of 90 days. Insect mortality was evaluated after 48 h. Pirimiphos-methyl residue decreased with increased storage time and grain temperature during spraying. Similar trends were also observed for mortality of S. zeamais and T. castaneum, which dropped from around 100% for lower grain temperatures, shortly after spraying, to mortality values around 0% for higher temperatures and after 90 days of storage. These results indicate the drastic effect of grain temperatures during spraying, which compromises the efficiency of grain protectants for insect pest control on stored grains. Key words: Sitophilus zeamais, Tribolium castaneum, organophosphate, residue, insect controlEficácia biológica e persistência do pirimifós-metil aplicados sobre grãos de milho em diferentes temperaturas RESUMO A técnica de seca-aeração pode causar problema no controle de insetos devido à alta temperatura do grão durante o processo de pulverização do inseticida. Com este trabalho objetivou-se avaliar o efeito imediato e latente da temperatura do grão durante o processo de pulverização sobre a persistência e eficácia biológica do inseticida pirimifós-metil no controle de Sitophilus zeamais e Tribolium castaneum. Para tal, pulverizou-se o inseticida pirimifós-metil sobre os grãos de milho quando se apresentavam nas temperaturas de 25, 30, 35, 40 e 45°C. A análise de resíduo foi realizada após a pulverização e a cada 30 dias, até 90 dias. Para avaliação da eficácia biológica 20 insetos adultos de S. zeamais e de T. castaneum foram colocados em uma placa de Petri contendo grãos tratados e, após 48 h de exposição dos insetos aos grãos, logo depois da pulverização e a cada 15 dias, até 90 dias, foram realizadas as avaliações. Observou-se que a eficácia biológica do pirimifós-metil reduziu durante o período de armazenamento e que o aumento da temperatura do grão no momento da pulverização também contribui para a redução da eficácia deste inseticida. Observou-se, também, que S. zeamais apresentou menor sensibilidade ao pirimifós-metil que T. castaneum. Palavras-chave:Sitophilus zeamais, Tribolium castaneum, organofosforado, resíduo, controle de inseto 1 UFVJM, CEP 39100-000, Diamantina, MG. Fone: (38) 3532-1226.

Evaluation of degradation of organophosphate insecticide residues in stored corn (Zea mays L.) grains

“…References: coefficient of determination (R 2 ) and half-life (HL-t 1/2 ). The residue decline (85 %) was consistent with other findings in cereal grains (Sgarbiero et al, 2003;Silveira et al, 2009;Strada et al, 2012), and in agreement with the physico-chemical characteristics of each active ingredient, as reported by Balinova et al (2006). These authors determined that, after 90 days of storage of wheat, CPM residues decreased by 60 % and that PMM residues decreased by only 30 %.…”

“…Even though this active principle is banned in Argentina and its use restricted to only some agricultural products in foreign legislation, the results of this work can be considered an important contribution on the dynamics of residues degradation. The dissipation of insecticide residues in other cereal grains, like wheat, has been extensively studied (Pal and Shah, 2008;Uygun et al, 2008;Lucini and Molinari, 2011), but that for maize is poorly known (Alleoni and de Baptista, 2001;Hamacher at al., 2002;Sgarbiero et al, 2003;Silveira et al, 2009). Pesticide trading companies must carry out tests to determine the POHI necessary to reach values below the MRL, but their studies are not available to estimate the residue levels after a pre-market application.…”

Diatomaceous earth effects on weevils with different susceptibility standard to phosphine

“…They are found in virtually all storage and processing units of Brazil (Pereira, et al, 2008;Aguiar et al, 2010). The control of these insects is done with the use of protective insecticides, organophosphates and pyrethroids and the fumigant aluminum phosphide Silveira et al, 2009;Sousa et al, 2009).…”