Effect of chlorpyrifos and monocrotophos on locomotor behaviour and acetylcholinesterase activity of subterranean termites, Odontotermes obesus.

The acute toxicity of chlorpyrifos and monocrotophos to subterranean termites, Odontotermes obesus (Rambur), has been studied by a paper contact method. The LC50 values for chlorpyrifos and monocrotophos were 0.046 and 0.148 microg cm(-2), respectively. Chlorpyrifos was 3.22-fold more toxic than monocrotophos. The effect of the pesticides on locomotor behaviour (velocity) and head acetylcholinesterase (AChE: EC 3.1.1.7) activity was estimated in LC50-exposed termites at intervals of 4, 8, 12, 16, 20 and 24 h. Chlorpyrifos- and monocrotophos-treated termites showed, respectively, 97 and 88% reduction in locomotor behaviour (velocity) after 24 h. At all time intervals the chlorpyrifos-treated termites exhibited more AChE inhibition and showed greater distorted behaviour than those exposed to monocrotophos. In vitro studies indicated that the I50 value (50% inhibition) for chlorpyrifos against AChE was 8.75 times that of monocrotophos.

Changes in behavior and brain acetylcholinesterase activity in mosquito fish, Gambusia affinis in response to the sub-lethal exposure to chlorpyrifos.

Sub-lethal studies of chlorpyrifos, O,O-diethyl-O-(3,5,6-trichloro-2-pyridyl) phosphorothioate on mosquito fish, Gambusia affinis were carried out in vivo, for 20 days to assess the locomotor behavior in relation to bioaccumulation and interaction with a targeted enzyme, acetylcholinesterase (AChE, EC: 3.1.1.7). Fish exposed to sub-lethal concentration of 60 microg/L (1/5 of LC 50) were under stress, and reduced their locomotor behavior like distance travelled per unit time (m/min) and swimming speed (cm/sec) with respect to the length of exposure. The alteration in locomotor behavior of fish may be due to an accumulation of acetylcholine (ACh), a neurotransmitter at synaptic junctions, due to the inhibition of AChE enzyme activity (40 to 55%) in brain and also bioaccumulation of the toxicant in different parts of fish. The bioaccumulation values indicated that the accumulation of chlorpyrifos was maximum in viscera followed by head and body. The average bio-concentration values are 0.109, 0.009 and 0.004 microg/g for viscera, head and body with depuration rates of 2.24, 1.69 and 0.39 ng/h respectively. It is evident from the results that the sub-lethal concentration [1/5 of LC 50; equivalent to Lowest Observed Effect Concentration (LOEC)] of chlorpyrifos can able to alter the locomotor behavior of G. affinis in relation to the length of exposure. The findings revealed that the locomotor activity of test organism could be considered as a suitable marker to evaluate the affect of toxicant even at LOEC levels.