Acute exposure to a neem based biopesticide and mahua oil cake changes haemocyte parameters in freshwater crab, Varuna litterata (Decapoda, Crustacea)

Abstract

Present study aims to evaluate the immunotoxic effects of two biopesticides, Nimbecidine Plus (a neem biopesticide) and mahua oil cake (MOC) on the haemocyte populations of a freshwater crab, Varuna litterata after acute exposure. Four-day static renewal bioassay test was performed where sixteen healthy adult male crabs were exposed to 96-h LC50 values of Nimbecidine Plus (0.006284 ppt) and MOC aqueous extract (7.631 ppt) separately in the laboratory condition. Control groups were maintained throughout the experimental period without any biopesticide exposure. Various haemocyte parameters such as total count (THC), differential count (DHC), haemocyte density, cytomorphological anomalies and reactive oxygen species (ROS) were measured in the biopesticides-exposed and control crabs after 24, 48, 72, and 96 h of exposure. After treatment with Nimbecidine Plus and MOC, several cytomorphological deformities (cytoplasmic and nuclear membrane disintegration, chromatin condensation, pyknosis, karyorrhexis, karyolysis, nuclear vacuolation, altered cell shape, cellular coagulation, cytoplasmic discharge, vacuolation) were observed in hyalinocytes, small granule haemocytes and large granule haemocytes with modulation of their relative percentages at different exposure times. THC, DHC, haemocyte density and ROS levels were significantly altered (p < 0.05) in biopesticides-exposed crabs at different exposure periods. The toxicity of both biopesticides did not persist throughout the entire exposure time. Nimbecidine Plus exhibited nonlinear toxic impacts on different haemocyte parameters at initial, mid and higher exposure periods whereas MOC showed linear toxic effects mostly at initial exposure time. In comparison to MOC, Nimbecidine Plus showed higher immunotoxic effects in V. litterata. Outcome of this experiment might provide useful information to understand the immune responses of V. litterata against biopesticide toxicity.