Six brands of commercial dichlorvos-vaporizing solids were tested individually in a 28.3 m3 test chamber simulating home conditions to evaluate their effective life. The dichlorvos vapor concentrations developed and maintained by the vaporizers in the chamber, varied from ca. 0.5 μg to 0.005 μg/liter during approximately a 2-month test period depending on the brand and ventilation of the test chamber. Any increase in ventilation correspondingly decreased the level of dichlorvos vapor concentration and vice versa. The vaporizing samples became depleted rapidly at higher than at lower rate of air exchange. At either rate of ventilation (1/3 or 1 air change/h) some of the samples, depending on their potentiality, were completely depleted whereas others produced very low concentrations during the 2-month exposure.

A 70–90 min exposure to a dichlorvos vapor concentration of ca. 0.1 μg/liter gave almost 100% mortality of susceptible and 85% of DDT-resistant caged female house fly, Musca domestica L. However, a similar exposure killed only 16% of the field-collected female house flies. When exposed, as free flying, to a similar concentration it took only 45 and 85 min to cause 95% kill of the susceptible and 85% kill of DDT-resistant house flies respectively. However, a 61/2 h exposure of field house flies to a similar concentration killed only 35.5% of them.

A dichlorvos concentration of ca. 0.1 μg/liter gave 100% kill of Tineola bisselliella (Hummel) larvae and Blattella germanica L. male adults in 6 and 3 days respectively, and of Aedes attopalpus Coquillett adults in a 30-min exposure. However, only 19% kill of Attagenus megatoma (F.) larvae occurred in 7 days with a similar concentration.