TRANSFER OF A LETHAL DOSE OF INSECTICIDE TO THE TARSI OF THE GERMAN-COCKROACH

The interaction of droplet size, droplet density, and insecticide conc entration on the time necessary for the tarsal pads to acquire a letha l dose was studied with male German cockroaches. A susceptible (VPI) a nd resistant-strain (RHA) was evaluated by direct application to the t arsi, and indirect application by cockroaches walking on 130 mum dia i nsecticide droplets on glass plates. The surface-contact area of the t arsal pads and the movement rate on insecticide-treated plates were de termined. The insecticide transferred to the tarsi was calculated with a formula incorporating the amount of movement per min, tarsal surfac e-contact area, and the amount of insecticide per cm2 on glass plates. Direct application data indicate that LDT50 and LDT90 are achieved wh en VPI cockroaches walk on at least 33 and 330 droplets of 0.1% cyperm ethrin, respectively. LDT50 would be achieved when RHA cockroaches wal ked on the residue of 3174 droplets. A KT50 and KT90 of 5.4 min and 7. 2 min, respectively, were recorded when VPI cockroaches walked on 10 m ug cypermethrin per cm2. The KT50 and KT90 increased to 8.4 min and 14 .1 min, respectively, when VPI cockroaches walked on 0.049 mug cyperme thrin/cm2. A mean KT50 and KT90 of 15.6 min and 27.5 min, respectively were recorded for RHA cockroaches walking on 10 mug cypermethrin/cm2. RHA had a KT50 of >24 hr on plates with 0.049 mug cypermethrin/cm2.