The Use of Log Dosage-Probit LDP Lines

It is now clear that an LDP line that is not straight may represent a resistant population. This may not be as obvious as it may seem. In the normal dose-response experiment with perhaps five groups of insects, there may be only three or four points with which the line is based (e.g., if one of the dose results in either 0% or 100% mortality). In this case, a real break or plateau in the curve could be overlooked. Tsukamoto (1963) discusses this problem and suggests that such experiments include more groups of insects, up to 8 to 10, in order that the direction of the line is more easily seen. 

An inadequate method of treating the insects will also result in a nonlinear line. It is assumed that the applied dose will always be proportional to the dose received. If this is not the case, however, we can see that some of the insects, probably those given the higher doses, will receive proportionally less than others. This could happen in topical applications or with residual exposure methods. Therefore, caution and care are required in performing dose-response tests in resistance studies (Terriere, 1982). 

Abbott, A.F., A method of computing the effectiveness of an insecticide, /. Econ. Entomoi, 18,1925. Anonymous, Health Effects Test Guidelines OPPTS 870.1300. Acute Inhalation Toxicity, United States Environmental Protection Agency, EPA 712-C-98-193,1998. 

Burchfield, H.P., Redder, A.M., Storrs, E.E., and Hilchey, J.D., Improved methods for rearing larvae of Aedes aegypti (L.) for use in insecticide bioassay, Contr. Boyce Thompson Inst., 17, 317,1953. 

Busvine, J.R., Critical review on the techniques for testing insecticides, London Commonwealth Agricultural Bureaux, 1971. 

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