Comportamento do gorgulho-do-milho frente às doses de permetrina

The maize weevil, Sitophilus zeamais Motsch. (Coleoptera: Curculionidae), is among the most destructive and globally well distributed pests of stored grain; the main method of control is the use of insecticides. This study aimed to compare, under laboratory conditions (27±2°C, 70%±10% RH, LD 12:12), the behavior of maize weevil populations exposed to different doses of the insecticide permethrin. Dose-response bioassays were conducted to determine CL50 values. Instantaneous rate of population growth, maize grain consumption and insect body mass were also determined at different permethrin concentrations. Insects were submitted to preference bioassays comparing permethrin-treated (insecticide residue) and untreated surfaces. Among the populations of Sitophilus zeamais used in bioassays, the population with the highest CL50 value was that of Palmeira, PI (127.7 µg i.a./cm2); the population with the lowest CL50 value was that of Balsas, MA (27.0 µg i.a./ cm2). Significant differences were observed among the permethrin concentrations with respect to instantaneous rate of population growth, consumption of dry maize grain biomass, insect body mass and number of adults emerged after 100 days. Regarding the behavior of S. zeamais adults, there was not significant discrimination in relation to the majority of concentrations; however, when compared to control, the proportion of individual insects that rejected the treated area was significant.O Gorgulho-do-milho, Sitophilus zeamais Motsch., 1855 (Coleoptera: Curculionidae), está entre as pragas mais destrutivas e mundialmente bem distribuídas dentre às de grãos armazenados, tendo como principal método de controle o uso de inseticidas. Este trabalho teve como objetivo comparar, em condições de laboratório (27±2ºC, 70%±10%UR, LD12:12), o comportamento de populações do caruncho do milho, expostas a diferentes doses do inseticida permetrina. Realizou- se bioensaios de concentração-mortalidade, para determinar os valores de CL50. Foi determinada à taxa instantânea de crescimento populacional (ri), o consumo de grãos de milho e a massa corporal dos insetos, em diferentes concentrações de permetrina. Os insetos foram submetidos aos bioensaios de preferência em superfície tratada e não-tratada com o inseticida. Dentre as populações de S. zeamais utilizadas nos bioensaios de concentração-mortalidade, a população que apresentou maior valor de CL50 foi a de Palmeira PI, 127,7µg i.a./cm2 e a que apresentou menor CL50 foi a de Balsas MA, 27,0µg i.a./cm2. Houve diferença significativa entre as concentrações de permetrina quanto à taxa instantânea de crescimento populacional (ri), consumo de biomassa seca dos grãos de milho, massa corporal dos insetos e número de adultos emergidos após 100 dias. Quanto ao comportamento de adultos de S. zeamais discriminantes, não houve um deslocamento significativo comparando as concentrações, no entanto em comparação ao controle a proporção de indivíduos que evitaram a área tratada foi significativa. Behavior of maize weevil at doses of permethrinAbstractThe maize weevil, Sitophilus zeamais Motsch. (Coleoptera: Curculionidae), is among the mostdestructive and globally well distributed pests of stored grain; the main method of control is the useof insecticides. This study aimed to compare, under laboratory conditions (27±2°C, 70%±10% RH,LD 12:12), the behavior of maize weevil populations exposed to different doses of the insecticidepermethrin. Dose-response bioassays were conducted to determine CL50 values. Instantaneousrate of population growth, maize grain consumption and insect body mass were also determinedat different permethrin concentrations. Insects were submitted to preference bioassays comparingpermethrin-treated (insecticide residue) and untreated surfaces. Among the populations of Sitophiluszeamais used in bioassays, the population with the highest CL50 value was that of Palmeira, PI(127.7 μg i.a./cm2); the population with the lowest CL50 value was that of Balsas, MA (27.0 μg i.a./cm2). Significant differences were observed among the permethrin concentrations with respectto instantaneous rate of population growth, consumption of dry maize grain biomass, insect bodymass and number of adults emerged after 100 days. Regarding the behavior of S. zeamais adults,there was not significant discrimination in relation to the majority of concentrations; however,when compared to control, the proportion of individual insects that rejected the treated area wassignificant