Ecotoxicology DOI 10.1007/s10646-017-1840-1 Bt i -based insecticide enhances the predatory abilities of the backswimmer Buenoa tarsalis (Hemiptera: Notonectidae) Yeisson Gutiérrez 1,2 ● Gabryele S. Ramos 1 ● Hudson V. V. Tomé 1,3 ● Eugênio E. Oliveira 1 ● Ana L. Salaro 4 Accepted: 19 July 2017 © Springer Science+Business Media, LLC 2017 Abstract 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 com- monly used in aquatic environments to control mosquitoes. Here, we evaluated whether insecticide formulations con- taining the bacterium Bacillus thuringiensis var. israelensis (Bt i ) 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 50 ) of B. tarsalis when exposed to Bt i -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 eval- uated 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 sig- nificantly reduced with pirimiphos-methyl concentrations ≥10 mg a.i./L, the Bt i -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 i -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 pre- dators exhibited reduced predatory abilities at the lowest prey density. Because they do not reduce the survival or the predatory abilities of B. tarsalis, Bt i -based insecticides can be considered a safe insecticide to use in the presence of backswimmers. Keywords Bacilus thuringiesnsis ● aquatic predators ● Natural enemies ● Pesticides Introduction Vector insects that convey human pathogens are recognized as a major health problem in tropical countries (WHO 2009). Among these insects, species belonging to the genera Culex and Aedes are widely distributed in Asia, Africa and Latin America, but the mosquito Aedes aegypti is especially notable due to its ability to transmit different types of arboviruses that include dengue fever, yellow fever, chi- kungunya and Zika (Moreira et al. 2009; Ndiaye et al. 2016; Barreto et al. 2016). The recent increase in human birth defects and deaths caused by mosquito-borne viruses has been reported as consequence of human movement (Adams and Kapan 2009), worldwide distribution of the vectors (Staples et al. 2009), and neglect, in the last decades, of prevention plans that include public awareness and the * Eugênio E. Oliveira eugenio@ufv.br * Ana L. Salaro salaro@ufv.br 1 Departamento de Entomologia, Universidade Federal de Viçosa, 36570-900 Viçosa, MG, Brazil 2 Institute of Landscape Ecology, University of Münster, 48149 Münster, Germany 3 EAG Laboratories, 13709 Progress Blvd #24 Suite S163, Alachua, FL 32615, USA 4 Departamento de Biologia Animal, Universidade Federal de Viçosa, 36570-900 Viçosa, MG, Brazil