Gerris spinolaeLethierry and Severin (Hemiptera: Gerridae) andBrachydeutera longipesHendel (Diptera: Ephydridae): Two Effective Insect Bioindicators to Monitor Pollution in Some Tropical Freshwater Ponds under Anthropogenic Stress

The abundance patterns of two insects, Gerris spinolae and Brachydeutera longipes, were found to be affected by abiotic aquatic factors including free carbon dioxide, dissolved oxygen, BOD, and phosphate concentrations prevailing in four tropical freshwater ponds, three of which being anthropogenically stressed. Regression analysis between each individual-independent water quality variable and insect abundance demonstrated a significant positive correlation in each case between B. longipes abundance and BOD, phosphate, free CO2, and algae dry weight, while a significant negative correlation of each of these variables was found with Gerris spinolae abundance. Moreover, a significant negative correlation of B. longipes abundance was calculated with dissolved oxygen concentration, while G. spinolae abundance exhibited a positive correlation with the same. Thus, G. spinolae appears to be a pollution sensitive, effective bioindicator for healthy unpolluted ponds, while B. longipes has potential as a pollution-resistant insect species indicative of pollution occurrence.