In laboratory tests, the mortality of sugar-beet wireworms, Limonius californicus (Mannerheim), in soil treated with shortlived insecticides was a function of the product of the concentration of insecticide multiplied by the time of exposure. In the field, Limonius spp. are transients in the upper (treated) layers of soil so the duration of exposure to soil treatments is largely fixed. Thus, the potency of a shortlived treatment in the field is primarily determined by its absolute toxicity and residual concentration. The relative potency of different non-persistent treatments can therefore change considerably with time. Dyfonate®(O-ethyl S-phenyl ethylphosphonodithioate), Bay 37289 (O-ethyl 0-2,4,5-trichlorophenyl ethylphosworms, in potency to the recommended standards, parathion and diazinon. The relative toxicity (based on the LD90 value) was parathion = diazinon = Dyfonate > Bay 37289> carbofuran. The relative persistence was Bay 37289 > Dyfonate > carbofuran = disunion > parathion. Thus, the initial relative potency of treatments with 4.5 kg/hectare of the chemicals was Dyfonate = diazinon = parathion> Bay 37289 = carbofuran, and 6–8 weeks after application the theoretical residual relative potency was Bay 37289 > Dyfonate> diazinon > parathion = carbofuran.