Deltamethrin toxicity and impaired swimming behavior of two backswimmer species.

Backswimmers (Hemiptera: Heteroptera: Notonectidae) are insect predators in a wide variety of freshwater habitats. These insects are well known through their role as mosquito biocontrol agents, their ability to prey on immature fishes and frogs, and because they are often the first to colonize aquatic habitats. As a consequence, these predators may face intended or unintended insecticide exposures that may lead to death or to impairment of essential behaviors (e.g., swimming and position in the water column). The toxicity of deltamethrin (a type II pyrethroid insecticide stressor) and the swimming activity of the backswimmers Buenoa tarsalis and Martarega bentoi were evaluated. Concentration-mortality and survival bioassays were conducted with the insecticide, which were compared with controls without deltamethrin. Deltamethrin was 26-fold more toxic to B. tarsalis (median lethal concentration [LC50] = 4.0 ng a.i./L) than to M. bentoi (LC50 = 102.5 ng a.i./L). The pattern of occupation of B. tarsalis, but not of M. bentoi, in the water column was also disrupted, and B. tarsalis was forced to stay near the water surface longer with exposure to deltamethrin. Thus, based on the findings, B. tarsalis was less resilient to deltamethrin exposure compared with M. bentoi, and the efficacy of swimming-dependent processes might be negatively affected (e.g., prey catching, partner encounter, and antipredator behaviors) for B. tarsalis under deltamethrin exposure. Environ Toxicol Chem 2017;36:1235-1242.