Synergism and unintended effects of the association between imidacloprid and sodium chloride (NaCl) on the management of Euschistus heros

Abstract

BACKGROUND: the use of insecticidal solutions containing sodium chloride (NaCl) has been proposed as a more environmen-tally friendly alternative to managing stink bug infestations of Neotropical soybeanfields. The potential sublethal and unde-sirable effects of this practice have, however, been overlooked, especially with novel insecticides. Here, we have evaluatedexperimentally whether the addition of NaCl (0.5%w/v) to imidacloprid-containing solutions could alter insecticide toxicityand modify the reproductive responses of the Neotropical brown stink bugEuschistus heros. RESULTS: addingNaCltoimidaclopridsolutionssignificantly increased imidacloprid toxicity againstE. heros. The exposure toE. herosto sublethal concentrations of imidacloprid affected the insect'smating abilities in a concentration-dependent manner. The additionof NaCl to solutions containing imidacloprid at concentrations as low as 0.126∼ga.i.cm−2(i.e. the equivalent to 3% offield rate rec-ommendation) also impacted the sexual behavior ofE. heros, reducing mating duration. NaCl-exposed stink bugs, however, exhibitedhigher fecundity and fertility rates than those insects that were unexposed to NaCl or those that were exposed to sublethal levels ofimidacloprid only. CONCLUSIONS: the addition of low amounts of NaCl resulted in a higher toxicity of imidacloprid. This practice, however, canalso lead to undesirable effects as increasing reproductive output of E. herosthat can potentially compromise the managementof these insect pests.