SummaryThe effectiveness of the synthetic pyrethroids deltamethrin and lambda‐cyhal‐othrin in preventing (i) aphid colonisation of four cowpea cultivars with different levels of aphid resistance and (ii) the introduction and subsequent spread of cowpea aphid‐borne mosaic virus and cucumber mosaic virus was investigated under tropical field conditions.Sprays of these pyrethroids eight days apart prevent aphid colonisation and within crop spread of virus by the colonisingAphis craccivora. However, neither deltamethrin nor lambda‐cyhalothrin prevented the initial introduction of virus into the cowpea crop and, when incoming alate incidence was high, virus incidence was higher in the sprayed than in the unsprayed plots. In addition, the degree of aphid resistance of each cultivar affected secondary virus spread within the crop, with greatest spread in the most resistant c