Osmotic Effects as a Factor Modifying Insecticide Toxicity onAedesandArtemia

Euryhaline species are more tolerant of various insecticides under isosmotic conditions. Two euryhaline species,Aedes taeniorhynchus(Wiedemann) andArtemiasp., were exposed to four insecticides (aldicarb, dimethoate, imidacloprid, tebufenozide), under isosmotic and hyperosmotic conditions. Mortality under these two osmotic conditions was observed and compared to evaluate salinity as a contributing factor to insecticide toxicity.Artemiawas more tolerant of all chemicals tested thanA. taeniorhynchusunder isosmotic conditions based on the percentage mortality observed. Mortality ofArtemiaunder isosmotic conditions was dependent on the length of exposure;A. taeniorhynchusdid not exhibit time dependence. Less mortality was observed in populations of both test species under isosmotic conditions compared with hyperosmotic conditions. However, the variation in mortality due to exposure to test chemicals was of greater magnitude inA. taeniorhynchusthanArtemia. This result indicates that higher salinity is a greater stress onA. taeniorhynchusthanArtemiawhen exposed to the test insecticides at the concentration ranges tested in this study.