Chemical pesticides and vegetal extracts on Sitophilus zeamais control in stored corn grains / Inseticidas químicos e extratos vegetais no controle de Sitophilus zeamais em grãos de milho armazenados

ABSTRACT

Sitophilus species are major pests of stored grain and their control is achieved mainly with the use of chemical insecticides, but the indiscriminate use of these products is resulting in several undesirable factors to man and to the environment. Thus, the use of natural insecticides comes as an option to control the insects, while lessening risks to the environment. The study was conducted at the Institute of Agricultural Sciences and Technologies, Rondonópolis campus of the Federal University of Mato Grosso, in the period from March to September 2012. The experiment was conducted under three different storing conditions. Aqueous extracts were obtained by the addition of Allium sativum L, Azadirachta indica A. Juss. and Cymbopogon winterianum Jowitt vegetable powders in distilled water, at a ratio of 5 g per 100 ml, and the levels of chemical insecticides were of 0.04 and 0.15 ml/100 ml of water for deltamethrin and chlorpyrifos, respectively. Treatments were added to the corn grains, which were placed in a 2.5 L glass container, mixed by manual shaking and infested with 20 adults of unsexed Sitophilus zeamais. Grains were stored for 60 days. At 30 and 60 days, the following items were analyzed bugs count, water content in grains and electrical conductivity. The data were submitted to analysis of variance, and means were compared by Tukey test at 5% probability. At 30 days, the efficiency of chemical insecticides in the control of Sitophilus zeamais was observed in the three storage environments. Vegetal extracts were not effective in controlling insects. The larger number of insects increased the electrical conductivity and humidity values in the grains.

RESUMO

O objetivo desse trabalho foi estudar o efeito inseticida de extratos vegetais aquosos e inseticidas químicos sob condições de armazenamento. O experimento foi realizado sob três condições de armazenamento. Os extratos aquosos foram obtidos pela adição dos pós vegetais de Allium sativum L, Azadirachta indica A. Juss. e Cymbopogon winterianum Jowitt. em água destilada na proporção de 5g por 100 ml, e as dosagens dos inseticidas químicos foram de 0,04 e 0,15 ml/100 ml de água para Deltametrina e Clorpirifós respectivamente. Os tratamentos foram adicionados aos grãos de milho acondicionados em recipientes de vidro de 2,5 L, misturados por agitação manual, e infestados com 20 adultos de Sitophilus zeamais não sexados. Os grãos ficaram armazenados durante 60 dias. Analisou-se aos 30 e 60 dias contagem de insetos, teor de água nos grãos e condutividade elétrica. Os dados foram submetidos à analise de variância, e as médias comparadas pelo teste de Tukey a 5 % de probabilidade. Aos 30 dias, observa-se eficiência dos inseticidas químicos no controle de Sitophilus zeamais nos três ambientes de armazenamento. Os extratos vegetais não são eficientes no controle dos insetos. O maior número de insetos elevam os valores de condutividade elétrica e umidade nos grãos.