Flight take-off and walking behavior of insecticide-susceptible and - resistant strains of Sitophilus zeamais exposed to deltamethrin.

Insects have evolved a variety of physiological and behavioral responses to various toxins in natural and managed ecosystems. However, insect behavior is seldom considered in insecticide studies although insects are capable of changing their behavior in response to their sensory perception of insecticides, which may compromise insecticide efficacy. This is particularly serious for insect pests that are physiologically resistant to insecticides since insecticide avoidance may further compromise their management. Locomotion plays a major role determining insecticide exposure and was, therefore, considered in investigating the behavioral responses of male and female adult insects from an insecticide-susceptible and two insecticide-resistant strains of the maize weevil Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae), a major pest of stored cereals. Different dose-dependent behavioral responses were expected among strains with behavioral resistance less likely to occur in physiologically resistant insects since they are able to withstand higher doses of insecticide. The behavioral responses to deltamethrin-sprayed surfaces differed among the maize weevil strains. Such responses were concentration-independent for all of the strains. Stimulus-independent behavioral resistance was unrelated to physiological resistance with one resistant strain exhibiting higher rates of flight take-off and the other resistant strain exhibiting lower flight take-off. Female mobility was similar for all strains, unlike male mobility. Males of each strain exhibited a pattern of mobility following the same trend of flight take-off. Behavioral patterns of response to insecticide are, therefore, variable among strains, particularly among insecticide-resistant strains, and worth considering in resistance surveys and management programs.

Enhanced activity of carbohydrate- and lipid-metabolizing enzymes in insecticide-resistant populations of the maize weevil, Sitophilus zeamais.

Insecticide resistance is frequently associated with fitness disadvantages in the absence of insecticides. However, intense past selection with insecticides may allow the evolution of fitness modifier alleles that mitigate the cost of insecticide resistance and their consequent fitness disadvantages. Populations of Sitophilus zeamais with different levels of susceptibility to insecticides show differences in the accumulation and mobilization of energy reserves. These differences may allow S. zeamais to better withstand toxic compounds without reducing the beetles' reproductive fitness. Enzymatic assays with carbohydrate- and lipid-metabolizing enzymes were, therefore, carried out to test this hypothesis. Activity levels of trehalase, glycogen phosphorylase, lipase, glycosidase and amylase were determined in two insecticide-resistant populations showing (resistant cost) or not showing (resistant no-cost) associated fitness cost, and in an insecticide-susceptible population. Respirometry bioassays were also carried out with these weevil populations. The resistant no-cost population showed significantly higher body mass and respiration rate than the other two populations, which were similar. No significant differences in glycogen phosphorylase and glycosidase were observed among the populations. Among the enzymes studied, trehalase and lipase showed higher activity in the resistant cost population. The results obtained in the assays with amylase also indicate significant differences in activity among the populations, but with higher activity in the resistant no-cost population. The inverse activity trends of lipases and amylases in both resistant populations, one showing fitness disadvantage without insecticide exposure and the other not showing it, may underlay the mitigation of insecticide resistance physiological costs observed in the resistant no-cost population. The higher amylase activity observed in the resistant no-cost population may favor energy storage, preventing potential trade-offs between insecticide resistance mechanisms and basic physiological processes in this population, unlike what seems to take place in the resistant cost population.

Volar transscaphoid perilunar dislocation.

A case of volar transscaphoid perilunar dislocation of the wrist with a follow-up of six months is described. Conservative treatment resulted in union of the scaphoid without avascular necrosis. The patient had a good functional result. In volar transscaphoid dislocations a conservative approach is proposed due to the preservation of vascular supply to the scaphoid in an injury caused by hyperflexion of the wrist.