Bt i -based insecticide enhances the predatory abilities of the backswimmer Buenoa tarsalis (Hemiptera: Notonectidae)

• Published in: Ecotoxicology (London) 2017-10, Vol.26 (8), p.1147
• Main Authors: Gutiérrez, Yeisson, Ramos, Gabryele S, Tomé, Hudson V V, Oliveira, Eugênio E, Salaro, Ana L
• Format: Article
• Language: English
• ISSN: 1573-3017

The backswimmer Buenoa tarsalis (Hemiptera: Notonectidae) is a naturally occurring predator of immature stages of mosquitoes. These aquatic predators can suffer from non-targeted exposure to insecticides that are commonly used in aquatic environments to control mosquitoes. Here, we evaluated whether insecticide formulations containing the bacterium Bacillus thuringiensis var. israelensis (Bt ) or the organophosphate pirimiphos-methyl would affect the survival and the predatory abilities of B. tarsalis. First, we conducted survival bioassays to estimate the median survival time (LT ) of B. tarsalis when exposed to Bt -based insecticide (at 0.25 and 25 mg a.i./L) and pirimiphos-methyl (at 1, 10 and 1000 mg a.i./L). The highest concentrations of the insecticides were equivalent to the label-recommended field rates. Second, the predatory abilities of B. tarsalis exposed to insecticides were evaluated at three prey densities (3, 6 and 9 mosquito larvae/100 mL water) just after insecticide exposure or after a 24 h recovery time. While the survival of B. tarsalis was significantly reduced with pirimiphos-methyl concentrations ≥10 mg a.i./L, the Bt -exposed predators exhibited similar survival as unexposed predators. Interestingly, after a recovery time of 24 h, B. tarsalis sublethally exposed to pirimiphos-methyl or Bt -based insecticide consistently killed more A. aegypti larvae (at the intermediate density) than unexposed predators. However, for the without-recovery bioassays, the pirimiphos-methyl-exposed predators exhibited reduced predatory abilities at the lowest prey density. Because they do not reduce the survival or the predatory abilities of B. tarsalis, Bt -based insecticides can be considered a safe insecticide to use in the presence of backswimmers.