Modified α-amylase activity among insecticide-resistant and -susceptible strains of the maize weevil, Sitophilus zeamais

Abstract

Fitness cost is usually associated with insecticide resistance and may be mitigated by increased energy accumulation and mobilization. Preliminary evidence in the maize weevil (Coleoptera: Curculionidae) suggested possible involvement of amylases in such phenomenon. Therefore, alpha-amylases were purified from an insecticide-susceptible and two insecticide-resistant strains (one with fitness cost [resistant cost strain], and the other without it [resistant no-cost strain]). The main alpha-amylase of each strain was purified by glycogen precipitation and ion-exchange chromatography (>or=70-fold purification, <or=19% yield). Single alpha-amylase bands with the same molecular mass (53.7kDa) were revealed for each insect strain. Higher activity was obtained at 35-40 degrees C and at pH 5.0-7.0 for all of the strains. The alpha-amylase from the resistant no-cost strain exhibited higher activity towards starch and lower inhibition by acarbose and wheat amylase inhibitors. Opposite results were observed for the alpha-amylase from the resistant cost strain. Although the alpha-amylase from the resistant cost strain exhibited higher affinity to starch (i.e., lower K(m)), its V(max)-value was the lowest among the strains, particularly the resistant no-cost strain. Such results provide support for the hypothesis that enhanced alpha-amylase activity may be playing a major role in mitigating fitness costs associated with insecticide resistance.

Insecticide Resistance Mechanisms in the Green Peach Aphid Myzus persicae (Hemiptera: Aphididae) I: A Transcriptomic Survey

“…It was evident the up-regulation of several key enzymes in metabolic pathways affecting glycolysis, gluconeogenesis, the Krebs cycle, galactose, lipids, and amino acid metabolism. This was consistent with the fact that insecticide resistance is usually associated with higher demands of energy in other insect species [7], [71], [72]. In other words, when facing insecticides, aphids of the S genotype experience an increase of general metabolism (both aerobic and anaerobic) that is accompanied by the mobilization of energy stores (glycogen and fats).…”

Use of Mutagenesis, Genetic Mapping and Next Generation Transcriptomics to Investigate Insecticide Resistance Mechanisms

“…The role of the proteolytic genes and genes showing peptidase activity in insecticide resistance is still poorly understood. There is increasing evidence of involvement of protein metabolism in insecticide resistances of different insect species [39], [40], [41], [42], [43]. Proteases may be involved in modification of enzyme conformation and protein biosynthesis, in order to meet energy requirements during xenobiotic stress [39].…”

Does cypermethrin affect enzyme activity, respiration rate and walking behavior of the maize weevil (Sitophilus zeamais)?

“…Insecticide exposure may impose changes to allow insect survival leading to altered patterns of digestion, energy metabolism and respiration rate (Orr & Downer, ; Hostetler et al ., ; Alaoui et al ., , ; Nath et al ., ; Harak et al ., ; Nath, , ; Ge et al ., ; Guedes et al ., ; Oliveira et al ., ; Araújo et al ., b; Silva et al ., ,b). Variation in such traits were observed among the key pest of stored maize in the neotropical region – the maize weevil Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae) (Guedes et al ., ; Oliveira et al ., ; Araújo et al ., ,b; Silva et al ., ,b; Lopes et al ., ), but their possible induction in different strains of this species has not yet been investigated and is the objective of the present study.…”