Abundance of Insect Predators and Water Quality of Two Different Aquatic Habitats in Galle District, Sri Lanka.

Abstract

Abstract Aquatic predatory insects play significant roles in keeping freshwater eco-systems. The study was conducted to compare the abundance of predatory aquatic insects, which could be possible predators of mosquito larvae witlf related to water quality of a waterbody in an urban area and a water body in a rural area in Galle district. The study was conducted from January to August in 2018. Insects were collected using a standard aquatic D frame net monthly and identified using taxonomic keys. Water quality parameters such as Temperature, pH, Conductivity, Turbidity, Salinity and DO were also measured. Insect predators belonged to orders Hemiptera, Coleoptera and Odonata were recorded from both habitats. Total of 255 (79.44%) individuals were recorded from the rural site, belonged to 11 types of families, Notonectidae, Veliidae, Hydrometridae, Naucoridae, Gerridae, Nepidae, Ranatridae, Dytiscidae, Hydrophilidae, Libellulidae and Chlorocyphidae. In the urban site, 66 (20.56%) individuals were recorded from the same 10 families except the family­Hydrometridae. Comparatively, the recorded abundance of predatorsin rural site was significantly higher than the urban site (P<0.05). The water temperature, pH, Conductivity, Turbidity and DO at rural site were 25.5±0.4°C, 6.98±0.25, 52±1.12 µS, 7.68±0.54 NTU, and 80.8±0.7 mg/L respectively, were significantly different from 7.68±0.54 NTU, and 80.8±0.7 mg/L respectively, were significantly different from the urban site coresponding values: 28.5±0.2°C, 7.78±0.75, 97.13±8.07µS, 17.58±1.18 NTU, and 3.2±1.3 mg/L (P<0.05) while water salinity of rural site (0.1±0.5 ppt,) and urban site (0.1±0.4 ppt,) were not significant. Pearson's correlation indicated that the abundance of natural enemies had positive correlations with the Temperature, pH, Conductivity, and the DO and negatively correlated with salinity in both sites. The study indicated that the selected rural habitat facilitated the abundance and high diversity of predators than the urban site.