ECOLOGY, BEHAVIOR AND BIONOMICS The Zygoptera/Anisoptera Ratio (Insecta: Odonata): a New Tool for Habitat Alterations Assessment in Amazonian Streams JMB OLIVEIRA-JUNIOR 1 ,LJUEN 2 1 Instituto de Ciências e Tecnologia das Águas, Univ Federal do Oeste do Pará, Santarém, Pará , Brasil 2 Lab de Ecologia e Conservação, Instituto de Ciências Biológicas, Univ Federal do Pará, Belém, Pará, Brasil Abstract Keywords Amazon, biomonitoring, dragonflies, damselflies, environmental change, lotic systems Correspondence JMB Oliveira-Junior, Instituto de Ciências e Tecnologia das Águas, Univ Federal do Oeste do Pará, Avenida Mendonça Furtado, no. 2946, Fátima, Santarém, Pará 68040-470, Brasil; maxbio@hotmail.com Edited by Edison Ryoiti Sujii – Embrapa/ CENARGEN Received 31 August 2018 and accepted 25 January 2019 * Sociedade Entomológica do Brasil 2019 The accumulation of scientific knowledge is far outstripped by the rate of environmental disturbance from human activities in aquatic habitats. This highlights the need to develop effective proxy measures of aquatic biodi- versity that can demonstrate changes in communities associated with hu- man activities. We evaluated whether the relative abundance and species richness of Anisoptera and Zygoptera can be used as a tool to measure environmental impacts on Amazonian streams. Adult of Anisoptera and Zygoptera were sampled in 50 Amazonian streams, in the municipality of Paragominas (Pará state), Brazil, using an entomological handnet. The phys- ical features of each stream were evaluated using an index of environmental integrity (HII). We collected a total of 1769 Odonata specimens, representing 97 species (56 were Zygoptera and 41 were Anisoptera). Habitat modifica- tion resulted in an inversion in the proportional abundance and species richness of Anisoptera and Zygoptera, where Zygoptera diversity decreased with the loss of habitat integrity, whereas Anisoptera diversity increased with habitat disturbance. A decline of 0.1 in the habitat integrity index score resulted in an increase of approximately 13 individuals and 11 species of Anisoptera, with the exact opposite effect observed for the Zygoptera. In summary, the Odonata proved to be a useful model for the assessment of Amazonian streams, with sites where more than 54% of the Odonata spe- cies were Zygoptera being classified as preserved, and those dominated by Anisoptera species (> 59%) being considered degraded. This approach has clear applications for environmental impact assessments, as it reduces the influence of sampling effort and collector experience on assessment out- comes, and does not rely upon specialist knowledge, given that members of the two suborders are easily distinguished from one and other in the field. Introduction Anthropogenic activities, including the removal and degrada- tion of natural habitats, have severely impacted aquatic eco- systems, resulting in major declines on aquatic biodiversity (Callisto et al 2001). Modification of physical-chemical char- acteristics of water (Couceiro et al 2007), deforestation, and increased siltation are the primary consequences of human occupation of drainage basins (Sponseller et al 2001 , Couceiro et al 2007, Monteiro-Júnior et al 2013, Carvalho et al 2013, Monteiro-Júnior et al 2016). These changes also tend to modify the structure (e.g., species richness and com- position) of local communities of aquatic organisms (Oertli 2008, Monteiro-Júnior et al 2013). Given this, studies that evaluate the relationship between environmental quality and the diversity of aquatic organisms have become increasingly important in recent years (Whittaker et al 2005). However, a number of factors Neotrop Entomol https://doi.org/10.1007/s13744-019-00672-x