A series of amides and esters of substituted benzo[b]furan-2-carboxylic acids have been synthesised, and their activity against adult sweet potato weevils, Cylas formicarius elegantulus (Summer) studied. The topical insecticidal potency of these compounds was compared in acetone solution and in a mixture of piperonyl butoxide (PB) and acetone (0·05+99·95 by volume). The compounds were much more active when administered in the acetone/PB mixture, and exhibited 48-h LD50 values ranging from 1·7 to 26·6 μg per insect. The most active compound, 2-(3,5-dimethylpyrazol-1-ylcarbonyl)-6-methoxy-3-methylbenzofuran, was equiactive with technical grade dimethoate (in acetone/PB) on a weight basis. © 1998 SCI