Organic phosphates of the formula: ##STR1## wherein R.sup.1 and R.sup.2 are respectively an alkyl group; R.sup.3 is a phenyl group which is substituted at least by a pyridazinyloxy or pyridazinylthio group in which the pyridazinyl group may be substituted; and X is an oxygen or sulfur atom, or a salt thereof, have marked insecticidal-acaricidal activity against plant pests and mites, household pests, with very low toxicity to warm-blooded animals and fish.