Susceptibilidad a endosulfan y monitoreo de resistencia en poblaciones de Piezodorus guildinii (Insecta, Heteroptera: Pentatomidae), en cultivos de soja de Argentina

The susceptibility status to endosulphan of different populations of P. guildinii (Westwood) that affect soybean crops in the Argentinean provinces of Santiago del Estero, Chaco and Santa Fe was determined. Also, to detect possible changes in P. guildinii response to the insecticide, resistance was monitored in a population of P. guildinii from Santiago del Estero from 2002 to 2005. Insects were collected from soybean fields in five localities, Oliveros, Reconquista, San Justo, Bandera and Coronel Du Graty. Topical bioassays were conducted in the laboratory, in the framework of standard World Health Organization test methods. The status of the susceptibility of the P. guildinii populations was: DL95 = 0,680μg/μL [0,489- 1,338] to 2,277μg/μL [1,526-5,418]. The results obtained suggest that the populations studied, which are geographically distant, show differences in their tolerance to endosulphan (detoxifying capabilities) that could be related to environmental factors and linked to any toxicocinetic or toxicodynamic processes. P. guildini populations studied show a trend towards increased tolerance to endosulphan from southern Santa Fe (Oliveros) to northern populations from Bandera (Chaco) that is probably related to environmental factors characteristic of each region. The population of P. guildinii monitored from 2002 to 2005 did not show an increase in tolerance to endosulphan with time. Population and environmental factors are both responsible for the temporal and spatial variations of susceptibility of a population to a biocide, making it hard to distinguish between phenotypic plasticity and susceptibility changes with a genetic basis. The soybean growing area in Argentina occupies a region with a huge range of climatic conditions and flora. In such a varied environment, phenotypic plasticity expressed by different P. guildinii should not be omitted, and should be differentiated from changes in susceptibility caused by genetic differences. Understanding the underlying mechanisms responsible for changes in susceptibility to pesticides, will allow us to distinguish between the effects of phenotypic plasticity and genetic changes and in turn this will aid in the selection of the appropriate measures for insect pest control. The susceptibility data on endosulphan obtained in this study will be useful for insecticide resistance monitoring and control failure diagnosis. Se determinó la susceptibilidad a endosulfan en diferentes poblacio