Resistência de populações do caruncho do milho a inseticidas fosforados

• Autor(a) principal: Freitas, Célia de Jesus Pereira
• Data de Publicação: 2007
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/4006
• topic: Sitophilus zeamais; Resistência a inseticidas; Comportamento; Compostos organofosforados; Custos adaptativos; Sitophilus zeamais; Resistance to insecticides; Behavior; Organophosphate compounds; Adaptative costs; CNPQ::CIENCIAS AGRARIAS::AGRONOMIA::FITOSSANIDADE::ENTOMOLOGIA AGRICOLA

Sitophilus zeamais Motsch. (Coleoptera: Curculionidae) is an important pest of stored maize because of the losses caused. This insect has been studied for responding to selection pressure for insecticide resistance, which impairs its control. In the present study, we carried out a survey of physiological and behavioral resistance to two organophosphate insecticides in 15 populations of S. zeamais collected in Brazil and Paraguay and investigated if differences in population growth, body size and metabolic rate were associated with the resistance. The insects were maintained in the laboratory, and concentration-mortality bioassays were conducted to determine lethal concentrations with 48 hours of exposure. Behavioral resistance was studied by recording the walking behavior on insecticide-treated and untreated surfaces and determining the distance walked, speed, resting time, and proportion of time spent on the treated surface. The instantaneous rate of population growth (ri) was determined, and so was the maize consumption for 90 days, body mass, and production of CO2 as indicative of the metabolic rate of the insects. Results of the concentration-mortality bioassays indicated variations in susceptibility to methyl clorpiriphos (≤ 6,06x) and fenitrothion (≤ 7,71x) relative to the standard susceptible population (Sete Lagoas), but these resistance levels are low and should not cause control failures in the field. The walking behavior on treated surfaces also varied among the populations, but no clear evidence of repellency was detected and no significant correlation was observed between physiological and behavioral resistance. The instantaneous rate of population increase and the respiratory rate were similar among the populations although there were differences in food consumption and body mass of the insects. Importantly, none of these four traits correlated with organophosphate resistance in the populations studied, suggesting absence of detectable fitness costs. We can conclude that the levels of resistance to methyl clorpiriphos and fenitrothion are low, and the physiological resistance in these populations is independent of the behavioral resistance. Furthermore, and even due to the low levels of organophosphate resistance detected, no fitness costs associated with insecticide resistance seems to occur.