Determination of Median Lethal Dose of Carbamate Insecticides Bendiocarb and Carbaryl in Garden Lizard, Calotes versicolor

Acute lethality usually determined as LD50 is defined as median dose predicted to kill 50 percent of a given test population. LD50 is a statistical estimate of the number of milligram of toxicant per kilo gram of body weight administered by any of the methods like oral, dermal, inhalation, or intravenous and is sufficient to kill 50 percent of the large population of test animals usually within certain time. Determination of LD50 has always been a much controversial subject among biologists and animal ethicists due to painful treatments on large number of animals. However, to assess the toxicity of various chemicals on different organisms Median lethal dose is still being used by toxicologists to determine acute lethality to non-target organisms. In the present study we aimed to determine the LD50 of two carbamate insecticides bendiocarb and carbaryl on a non-target species Calotes versicolor a reptilian model. An approximate LD50 was initially determined as a pilot study by a so called ‘staircase method’ using only 2 animals (for each dose) and increasing the doses of the drug. Five doses 10, 15, 20, 25, 30 mg/kg body weight for bendiocarb and 50, 60, 70, 80, 90 mg/kg body weight for carbaryl were chosen for determination of LD50 starting from no death to 100% mortality. Intraperitoneal LD50 value calculated by regression analysis is 15.57 and 64.97 mg/kg body weight for bendiocarb and carbaryl respectively in male Calotes versicolor. The result confirms that bendiocarb is more potent than carbaryl in Calotes suggesting that bendiocarb may cause death even at smaller doses in comparison to carbaryl. Our results will help in adding to the fact sheet related to carbamate toxicity in reptiles.