Acute Toxicity of Imidacloprid to Various Life Stages of the Giant Freshwater Prawn Macrobrachium rosenbergii, de Man, 1879

Abstract

The present study was conducted invitro to evaluate the acute toxicity of a broad spectrum neonicotinoid, imidacloprid used by farmers contently to control piercing-sucking pests in the paddy fields of Kuttanad, a part of the Vembanad wetland ecosystem which is a Ramsar site of international importance in the state of Kerala, India, to various life stages of Macrobrachium rosenbergii, a commercially important indigenous prawn of Kuttanad. The median tolerance limit (LC50) were calculated using the observations made on the mortality of prawns exposed to 5 different concentrations between the No Observable Effect Concentration (NOEC) and Lowest Observable Effect Concentration (LOEC) of biocides for a period of 96 h. LC50 values for 24, 48, 72 and 96 h of imidacloprid was determined by probit analysis using SPSS version 16.0. The study revealed that the 96 h LC50 concentrations for imidacloprid as 0.009, 5.0234 and 42.611 mg/l in post-larvae (0.041 ± 0.02 g), juvenile (3.5 ± 1.5 g) and adult (17.5 ± 2.5 g), respectively of M. rosenbergii. Based on the LC50 values, safe concentrations found out for imidacloprid using Hart’s formula were 0.002, 1.000 and 15.138 mg/l, in post-larvae, juvenile and adult M. rosenbergii, respectively. The field application concentration of imidacloprid is 0.003 mg/l which is 3 times higher than the safe concentration of imidacloprid in post-larvae, whereas it is lower than the safe concentration in juvenile and adult M. rosenbergii. The results revealed that the application of imidacloprid in the paddy fields of Kuttanad has a lethal effect on post-larvae of M. rosenbergii causing a threat to the existence of species in its homeland.