Residual efficacy of four organophosphate insecticides on concrete and galvanized steel surfaces against three Liposcelid psocid species (Psocoptera: Liposcelidae) infesting stored products

Four organophosphate insecticides, azamethiphos, fenitrothion, chlorpyrifos-methyl, and pirimiphos-methyl, were tested as surface treatments on concrete (porous surface) and galvanized steel (nonporous surface) panels (0.3 Ly 0.3 m) against adults of three Liposcelid psocid spp.--Liposcelis bostrychophila Badonnel, Liposcelis entomophila (Enderlein), and Liposcelis pacta Pearman. Residual efficacy of these chemicals was assessed at 30 +/- 1 degrees C, 70 +/- 2% RH, and a photoperiod of 12:12 (L:D) h from 1 d after treatment (0 wk) and thereafter at reeks 1, 2, 4, 6, and 8, and then every 4 wk up to reek 40. Mortality was recorded at exposure periods of 6 h and then every 24 h until end-point was achieved. L. bostrychophila was the most susceptible species to the organophosphates tested, followed by L. pacta and L. entomophila. We conclude that for long-term protection, azamethiphos is the preferred organophosphate against L. bostrychophila (up to 36 uk on steel and 24 wk on concrete storage sm faces) and L. pacta infestations only on steel surface (up to 28 wk). None of the four organophosphates tested, however, would provide long-term protection against L. pacta on concrete surface and against L. entomophila infestations on either concrete or steel storage surfaces.