Results of dose response bioassays 'in vivo' used to characterise the phenotypic response of pyrethroid resistant S. avenae in comparison to susceptible S. avenae, and two other cereal aphids, the rose-grain aphid (Metopholophium dirhodum) and the bird-cherry – oat aphid (Rhopalosiphum padi), are used to measure levels of pyrethroid resistance. Aphid pests on cereals in the British Isles are predominantly controlled by pyrethroid insecticides, especially since the implementation of the recent ban on neonicotinoid seed treatments on all outdoor crops. Resistance to pyrethroids has been detected in one of the main aphid pests, the grain aphid (Sitobion avenae), probably brought on by the sustained use of these pyrethroid sprays to control cereal aphids, which can transmit plant viruses, especially Barley Yellow Dwarf Virus (BYDV). The withdrawal of several insecticide compounds (e.g. pirimicarb, dimethoate, chlorpyrifos and the aforesaid neonicotinoids) for cereal aphid control will probably increase the selection pressure, leading to increased levels of resistance in S. avenae, and, potentially, the evolution of resistance in other cereal aphid species. In this article we present the results of dose response bioassays 'in vivo' used to characterise the phenotypic response of pyrethroid resistant S. avenae in comparison to susceptible S. avenae, and two other cereal aphids, the rosegrain aphid (Metopholophium dirhodum) and the bird-cherry– oat aphid (Rhopalosiphum padi), in order to measure levels of pyrethroid resistance. At present, little is known about the extent of pyrethroid resistance in S. avenae beyond the UK and in other cereal aphids. It therefore becomes increasingly important to monitor these pests to inform crop management decisions in light of the recent loss of other insecticides. The unintended consequences of the rapid withdrawal of insecticides, together with a failure to prepare and install alternative products and control approaches in advance, will probably ultimately lead to the loss of effectiveness of insecticidal compounds like pyrethroids.