Effects of pesticides with different mechanism of toxicity in the freshwater prawn Macrobrachium borellii

Abstract

Synthetic pyrethroids like cypermethrin (CYP) are extensively applied for control of agricultural pests and disease vectors. However due to its harmful consequences to non-target organisms, the bioinsecticides represents a benign and desirable alternative to the environment. Among them the biological insecticide produced from Bacillus thuringiensis israelensis (Bti) is mainly used for the control of mosquito vectors of diseases like dengue. Anyway, pest organisms have developed resistance mechanisms to such kind of insecticides so last generation pesticides, such as the tetramic acid spirotetramat (STM), have recently emerged. Due to the limited information available on the effect of these compounds on non-target species, the effect of CYP, Bti and STM on the freshwater prawn Macrobrachium borellii was analyzed. Initially, the LC50-96 h was determined in adult prawns (males and females in non-vitellogenic state), by serial dilutions of the three insecticides. A negative control without insecticides was included. Then, in order to determine metabolic disorders that could be used as biomarkers of pollution, prawns were exposed to sublethal concentrations of CYP (0.006 and 0.02 μg /L), Bti (0.04 and 0.4 mg /L) andSTM (0.5 and 1.7 mg/L) for 4 days. The levels of lipid peroxidation (LPO) and protein oxidation (OP), as well as the presence of histopathological changes were evaluated in the hepatopancreas. The LC50-96 h values were 0.8 and 8.2 mg /L for Bti and STM respectively, and 0.12 μg /L for CYP. All three insecticides significantly affected the LPO and OP levels in this organ (p < 0.05). Pesticides caused histopathological alterations in the hepatopancreas of the exposed prawns, such as atrophy in the epithelium of the digestive tubules, necrosis of the epithelial cells, and the infiltration of hemocytes into the connective tissue between the intertubular space. This study showed that M. borellii is less sensitive than other crustaceans to CYP. In addition they are the first results of sensitivity to Bti and STM in this taxonomic group. Considering that the hepatopancreas is the main organ for toxicant metabolism in crustaceans, these results indicate that oxidative status in M. borellii is very sensitive to these insecticides. Therefore, this prawn could be proposed as useful bioindicator to monitor freshwater environments that are exposed to these pollutants.