TY - JOUR T1 - Deltamethrin-induced feeding plasticity in pyrethroid-susceptible and -resistant strains of the maize weevil, Sitophilus zeamais JF - Journal of Applied Entomology Y1 - 2009 A1 - Guedes, N. M. P. A1 - Guedes, R. N. C. A1 - Silva, L. B. A1 - Cordeiro, E. M. G. SP - 524 EP - 532 KW - Sitophilus zeamais AB - Phenotypic plasticity contributes to the adaptative evolution of populations exposed to new or altered environments. Feeding plasticity is a component of phenotypic plasticity not usually considered in insect strains adapted to insecticide-altered environments, but which may either accentuate or mitigate insecticide resistance. This is a concern in the pyrethroid-resistant strains of the maize weevil Sitophilus zeamais Motsch. (Col., Curculionidae), and the reason for this study. A pyrethroid-susceptible and two pyrethroid-resistant strains of maize weevil were subjected to free-choice and no-choice tests with maize grains sprayed with increasing doses of the pyrethroid, deltamethrin. The insects from the pyrethroid-resistant strains exhibited higher feeding avoidance with increased deltamethrin doses than insects from the susceptible strain when subjected to free-choice tests. The strains of maize weevil physiologically resistant to pyrethroids were also behaviourally resistant to deltamethrin [long dash] an additional management concern. The resistant strains avoid deltamethrin-sprayed grains and are less nutritionally affected by this compound, with divergent responses from the susceptible strain with increased doses of deltamethrin. Furthermore, the higher relative growth rate and consequently higher efficiency of food conversion observed in the insecticide-resistant strains were significant even without insecticide exposure, indicating that these traits are stimulus-independent and may persist even without further insecticide selection, potentially limiting the options available for their management. VL - 133 SN - 0931-2048 ER - TY - JOUR T1 - Insecticide-induced hormesis in an insecticide-resistant strain of the maize weevil, Sitophilus zeamais JF - Journal of Applied Entomology Y1 - 2010 A1 - Guedes, N. M. P. A1 - Tolledo, J. A1 - Correa, A. S. A1 - Guedes, R. N. C. SP - 142 EP - 148 KW - Sitophilus zeamais AB - Sublethal responses to insecticides are frequently neglected in studies of insecticide resistance, although stimulatory effects associated with low doses of compounds toxic at higher doses, such as insecticides, have been recognized as a general toxicological phenomenon. Evidence for this biphasic dose-response relationship, or hormesis, was recognized as one of the potential causes underlying pest resurgence and secondary pest outbreaks. Hormesis has also potentially important implications for managing insecticide-resistant populations of insect-pest species, but evidence of its occurrence in such context is lacking and fitness parameters are seldom considered in these studies. Here, we reported the stimulatory effect of sublethal doses of the pyrethroid insecticide deltamethrin sprayed on maize grains infested with a pyrethroid-resistant strain of the maize weevil (Sitophilus zeamais) (Coleoptera: Curculionidae). The parameters estimated from the fertility tables of resistant insects exposed to deltamethrin indicated a peak in the net reproductive rate at 0.05 ppm consequently leading to a peak in the intrinsic rate of population growth at this dose. The phenomenon is consistent with insecticide-induced hormesis and its potential management implications are discussed. VL - 134 SN - 0931-2048 ER - TY - JOUR T1 - Flight take-off and walking behavior of insecticide-susceptible and -resistant strains of Sitophilus zeamais exposed to deltamethrin JF - Bulletin of Entomological Research Y1 - 2009 A1 - Guedes, N. M. P. A1 - Guedes, R. N. C. A1 - Ferreira, G. H. A1 - Silva, L. B. SP - 393 EP - 400 KW - Sitophilus zeamais AB - 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. VL - 99 SN - 0007-4853 ER - TY - JOUR T1 - Bidirectional selection for body mass and correlated response of pyrethroid resistance and fitness in Sitophilus zeamais JF - Journal of Applied Entomology Y1 - 2011 A1 - Correa, A. S. A1 - Tolledo, J. A1 - Pereira, E. J. G. A1 - Guedes, R. N. C. SP - 285 EP - 292 KW - Sitophilus zeamais AB - Responses to artificial selection on body mass in the maize weevil Sitophilus zeamais (Coleoptera: Curculionidae) were investigated to determine whether changes in body mass are associated with insecticide susceptibility, rate of population growth, and metabolic rate. Two strains of the maize weevil differing in susceptibility to pyrethroid insecticides were subjected to bidirectional selection on body mass. The susceptible strain responded to selection resulting in individuals with lower or higher body mass, but the resistant strain responded significantly only to selection for lower body mass. The resistant strain selected for low body mass increased its level of deltamethrin resistance in 44 x . In contrast, selection for low body mass in the susceptible parental strain led to increased deltamethrin susceptibility (50 x ) and selection for high body mass increased deltamethrin resistance (4 x ). Thus, the correlated response of insecticide resistance to selection for body mass differed between strains, a likely consequence of their distinct genetic background. Regardless, body mass was positively correlated with fitness (reproductive output) (r = 0.79; P < 0.001), while such correlation with respiration rate was significant only at P = 0.07 (r = 0.44). Therefore, the association between body mass and deltamethrin resistance is population-dependent in the maize weevil, and the confluence of deltamethrin resistance and high body mass in a given strain will likely favour its energy metabolism and lead to the mitigation of fitness costs usually associated with insecticide resistance. The genetic background and selection history of insecticide resistant populations should not be neglected since they may favour the confluence of insecticide resistance with mitigation mechanisms of its associated fitness costs limiting the tactics available to their management. VL - 135 SN - 0931-2048 ER - TY - JOUR T1 - Insecticide resistance, mixture potentiation and fitness in populations of the maize weevil (Sitophilus zeamais) JF - Crop Protection Y1 - 2011 A1 - Correa, A. S. A1 - Pereira, E. J. G. A1 - Cordeiro, E. M. G. A1 - Braga, L. S. A1 - Guedes, R. N. C. SP - 1655 EP - 1666 KW - Sitophilus zearnais AB - High levels of pyrethroid resistance and emerging organophosphate resistance in Brazilian populations of the maize weevil Sitophilus zearnais (Coleoptera: Curculionidae) led to the registration of esfenvalerate + fenitrothion against them. Thus, a survey of physiological and behavioural resistance was carried out in 27 insect populations for two pyrethroids, esfenvalerate and permethrin, and the esfenvalerate + fenitrothion mixture. Physiological resistance to fenitrothion was also assessed, as was the potentiation of the mixture. The potential fitness cost associated with insecticide resistance was also investigated. The resistance levels were low to fenitrothion (<14.1-fold), low to moderate to the pyrethroids (1.6-70.0-fold) and low to the pyrethroid-organophosphate mixture (<5-fold) with a high heterogeneity of response among populations. The potentiation of insecticidal activity achieved with the insecticide mixture was very high (>350-fold) reinforcing its usefulness for managing weevils. There was little variation in walking behaviour (and insecticide avoidance) among populations: there was no significant variation in fitness, body mass and respiration rate among the populations of the insect. These however, displayed variable rates of grain consumption and activity of amylase and lipase. A decrease in insecticide resistance in maize weevil populations was observed relative to previous studies, but with an initial development of resistance to the insecticide mixture. Behavioural and physiological resistance were not correlated and not associated with fitness cost. Our results support the use of esfenvalerate + fenitrothion against the maize weevil, which is likely to have reduced the levels of pyrethroid resistance in field populations. However, resistance to this mixture seems to be evolving, justifying concerns regarding its use. (C) 2011 Elsevier Ltd. All rights reserved. VL - 30 SN - 0261-2194 ER - TY - JOUR T1 - Face or flee? Fenitrothion resistance and behavioral response in populations of the maize weevil, Sitophilus zeamais JF - Journal of Stored Products Research Y1 - 2011 A1 - Braga, L. S. A1 - Correa, A. S. A1 - Pereira, E. J. G. A1 - Guedes, R. N. C. SP - 161 EP - 167 AB - Insect survival in the presence of contact insecticides may be through physiological mechanisms or avoidance of contact with the compound. Curiously, although the first alternative is the object of frequent attention, the second is often neglected, but both may lead to insecticide resistance. Preliminary evidence for both physiological and behavioral resistance to pyrethroids has been obtained for a few strains of the maize weevil Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae). Here we carried out a more comprehensive survey using 15 populations of S. zeamais, by examining a long-used but relatively little studied organophosphate - fenitrothion, recording not only physiological resistance, but also the behavioral responses to exposure. Physiological resistance to fenitrothion among populations of S. zeamais reached low to moderate levels (ranging from 0.9 to 14.1 x at the LC50), an increase in resistance levels compared with previous studies. Fenitrothion-induced behavioral avoidance varied among populations, particularly regarding insecticide irritability (i.e., avoidance after contact with fenitrothion), but the behavioral responses observed were mainly stimulus-independent. However, there was no correlation between physiological and behavioral resistance to fenitrothion in S. zeamais populations. Both survival strategies to fenitrothion - facing or fleeing the insecticide exposure, were observed and may co-occur in a single population, emphasizing the need of assessing both responses and their relative importance in designing management programs against stored-product insects. [copyright] 2011 Elsevier Ltd. All rights reserved. VL - 47 SN - 0022-474X ER - TY - JOUR T1 - Enhanced activity of carbohydrate- and lipid-metabolizing enzymes in insecticide-resistant populations of the maize weevil, Sitophilus zeamais JF - Bulletin of Entomological Research Y1 - 2008 A1 - Araujo, R. A. A1 - Guedes, R. N. C. A1 - Oliveira, M. G. A. A1 - Ferreira, G. H. SP - 417 EP - 424 KW - Sitophilus zeamais AB - 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. VL - 98 SN - 0007-4853 ER - TY - JOUR T1 - Enhanced proteolytic and cellulolytic activity in insecticide-resistant strains of the maize weevil, Sitophilus zeamais JF - Journal of Stored Products Research Y1 - 2008 A1 - Araujo, R. A. A1 - Guedes, R. N. C. A1 - Oliveira, M. G. A. A1 - Ferreira, G. H. SP - 354 EP - 359 KW - Sitophilus zeamais AB - Insecticide resistance is frequently associated with fitness costs in the absence of insecticides, but extended and intense past selection with these compounds may favor the evolution of fitness modifier genes that mitigate such costs. Insecticide resistance without fitness cost was associated with greater accumulation of total proteins and carbohydrates in a strain of the maize weevil (Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae)). Increased energy reserves may be due to an accumulation of carbohydrates and proteins because of increased digestive efficiency. To test this hypothesis, proteases and enzymes (cellulase and the pectinases polygalacturonase and pectin lyase), which enable insects to access the nutrients, were used to compare digestive efficiency in insecticide-susceptible and -resistant strains of the maize weevil. A canonical variate analysis indicated significant differences among the strains in enzyme activities, and kinetic parameters were calculated. Serine- and cysteine-proteinases as well as cellulase activities were smaller in susceptible than resistant strains. In addition, the esterolytic activity of serine-proteinases was most increased in the insecticide-resistant strain exhibiting a fitness disadvantage associated with insecticide resistance. Overall, enzymes in the insecticide-resistant strains had increased serine- and cysteine-proteolytic and cellulolytic activity, and kinetic parameters suggested that cysteine-proteinase and cellulase activities were more important in mitigating the cost of insecticide resistance in maize weevil strains. VL - 44 SN - 0022-474X ER -