ABSTRACT
Toxic interactions of an insecticide with a biological system are dose dependent. The toxicity of an insecticide to an organism is usually expressed in terms of LD50 (lethal dose). This value represents the dose per unit weight lethal to 50% of the population of the organism. The LD50 is commonly expressed as milligrams per kilogram (mg/kg). In some cases, the LC50 (lethal concentration) is used to express the concentration of the insecticide in the external media that will kill half of the test population because the exact dose initially given to the insect cannot be determined. For example, the toxicity of insecticides to mosquito larvae is commonly expressed as LC50. The term LT50 is occasionally used to express the toxicity of insecticides. This value represents the time required to kill 50% of the test population at a certain dose or concentration. This method of evaluating toxicity requires relatively few individuals and therefore is often used for eld tests where a large number of individuals cannot be collected. Sometimes, the rate of knockdown of insects becomes a more important criterion for determining the toxicity of insecticides than the rate of kill. In such cases, the KD50 and KT50 are used to express the median knockdown dose and knockdown time, respectively. The ED50 and EC50 are also used to express 50% effective dose and 50% effective concentration, respectively, when some criteria of toxicity other than death are adopted (e.g., fertility and fecundity). For instance, in tests with chemosterilants, the purpose is to cause sexual sterility of the test insects but not to kill them. Readers interested in bioassays with arthropods are referred to a useful book by Robertson et al. (2007).
