The efficacy of insecticide–silica mixtures depended on brand of silica, i.e. Ar6gen®500, Hi-Sil®233, Micro-Cel®A, and Zeolex®100; number and population density of pest species; and cultivar of potato. In greenhouse tests, changes in the proportions of carbaryl and Arogen®500 in mixtures did not change efficacy; a 600 ppm carbaryl – 5400 ppm Arogen®500 mixture was as good as 1000 ppm carbaryl; and mixtures with either phosmet or pirimiphos-methyl and any silica with 30 ppm of insecticide and 270 ppm of silica were as good as 100 ppm of insecticide using mortality, repellency, and feeding rate as criteria. In the field at high density of L. decemlineata and low aphids, a 600 ppm carbaryl – 5400 ppm Arogen-500 mixture reduced larval populations by 66% and increased yield of Irish Cobbler 18-fold; and foliage treated with a 2000 ppm phosmet – 18,000 ppm Arogen-500 mixture was less attractive to adults than foliage treated with 2000 ppm of phosmet though the mixture was not superior to phosmet in effects on yield. At medium density of L. decemlineata and low aphids, a 500 ppm pirimiphos-methyl – 4500 ppm Zeolex-100 mixture increased yield of Irish Cobbler by about 100% and of Sebago by about 200% and a 600 ppm carbaryl – 5400 ppm Arogen-500 mixture was about 32% better than 1300 ppm carbaryl in effects on yield of Sebago. At low density of L. decemlineata and high density of aphids, 1000 ppm of carbaryl and various mixtures of carbaryl and Arogen-500 increased aphids by 109%, reduced coccinellid predators by one third, and reduced yield of Irish Cobbler and Sebago by 12%.