01975nas a2200193   4500008004100000020001400041245010800055210006900163260000800232300001200240490000800252520129500260653002301555100002201578700001601600700001901616700002201635856012401657       2010                        eng d  a0931-204800aInsecticide-induced hormesis in an insecticide-resistant strain of the maize weevil, Sitophilus zeamais0 aInsecticideinduced hormesis in an insecticideresistant strain of  cMar  a142-1480 v1343 aSublethal 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.10aSitophilus zeamais1 aGuedes, N., M. P.1 aTolledo, J.1 aCorrea, A., S.1 aGuedes, R., N. C.  uhttps://weevil.myspecies.info/insecticide-induced-hormesis-insecticide-resistant-strain-maize-weevil-sitophilus-zeamais02603nas a2200193   4500008004100000020001400041245012500055210006900180260000800249300001200257490000800269520189400277653002302171100001902194700001602213700002302229700002202252856013502274       2011                        eng d  a0931-204800aBidirectional selection for body mass and correlated response of pyrethroid resistance and fitness in Sitophilus zeamais0 aBidirectional selection for body mass and correlated response of  cMay  a285-2920 v1353 aResponses 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.10aSitophilus zeamais1 aCorrea, A., S.1 aTolledo, J.1 aPereira, E., J. G.1 aGuedes, R., N. C.  uhttps://weevil.myspecies.info/bidirectional-selection-body-mass-and-correlated-response-pyrethroid-resistance-and-fitness-sitophil02659nas a2200205   4500008004100000020001400041245011700055210006900172260000800241300001400249490000700263520191900270653002402189100001902213700002302232700002402255700001802279700002202297856013402319       2011                        eng d  a0261-219400aInsecticide resistance, mixture potentiation and fitness in populations of the maize weevil (Sitophilus zeamais)0 aInsecticide resistance mixture potentiation and fitness in popul  cDec  a1655-16660 v303 aHigh 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.10aSitophilus zearnais1 aCorrea, A., S.1 aPereira, E., J. G.1 aCordeiro, E., M. G.1 aBraga, L., S.1 aGuedes, R., N. C.  uhttps://weevil.myspecies.info/insecticide-resistance-mixture-potentiation-and-fitness-populations-maize-weevil-sitophilus-zeamais02346nas a2200181   4500008004100000020001400041245012100055210006900176260000800245300001200253490000700265520167500272100001801947700001901965700002301984700002202007856013502029       2011                        eng d  a0022-474X00aFace or flee? Fenitrothion resistance and behavioral response in populations of the maize weevil, Sitophilus zeamais0 aFace or flee Fenitrothion resistance and behavioral response in   cJul  a161-1670 v473 aInsect 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.1 aBraga, L., S.1 aCorrea, A., S.1 aPereira, E., J. G.1 aGuedes, R., N. C.  uhttps://weevil.myspecies.info/face-or-flee-fenitrothion-resistance-and-behavioral-response-populations-maize-weevil-sitophilus-zea