Mat and liquid-type electric insecticide vaporizers continuously emit insecticides into the surrounding air. Because both the target insects, mostly mosquitoes, and humans are exposed to those insecticides, it is crucial to understand and monitor their deposition and spatial distribution in treated areas. In the current study, we examined the evaporation of insecticides from seven commercial liquid and mat vaporizers and measured their knock-down and insecticidal activity against the adult females of the Asian tiger mosquito, Aedes albopictus (Skuse). Electric vaporizers from three manufactures had differences in their heaters and active ingredients. Most had continued evaporation during hourly and daily monitoring; however, some liquid vaporizers failed to continue emission to their designated end periods. Overall, mosquitoes located at the upper position in a Peet-Grady chamber and in a field-simulation room exhibited faster knock-down activity than did mosquitoes in other areas, indicating that the insecticides accumulated on the ceiling area. Although most of mat and liquid vaporizers had <60 min of average KT90 values when tested in the Peet-Grady chamber (1.8 × 1.8 × 1.8 m), they failed to have any knock-down in 2 h of observation in the field-simulation room (6.8 × 3.4 × 2.7 m) but showed 72. 8 ± 11.7% and 56. 7 ± 7.3% knock-down in the mat and liquid vaporizers, respectively, in 3 h of operation. Further study will be required to examine whether this relatively limited efficacy can be compensated by other physiological and behavioral effects, including disruption in host-seeking or blood-sucking activities.
For the indoor and outdoor pest controls, various types of insecticide formulations are available including aerosols, sprays, electric vaporizers, mosquito coils, and traps. In the present study, the insecticidal activity of aerosols, the most commonly used formulation of household insecticides for mosquito control, against Aedes albopictus (Skuse) was assessed using seven commercial products and some attributes which can affect the efficacy of aerosol were investigated as well. The products had difference in their chemical composition of active ingredients, propellant/liquid phase ratios, solvent types, and nozzle orifice sizes, and these characteristics seem to affect the overall insecticidal activity. In general, solvent type dominantly determined the insecticidal activity, where four products in oil-based solvent system showed greater mortality (97.5% in average) than water-based aerosols (38.3% in average) against the mosquitoes located at the far side of the test chamber. The contribution of solvent type and nozzle orifice size were further examined with the sample aerosols, and the orifice size were determined more influential to the spray distance. Regardless of solvent types, the sample products attached to a bigger actuator (0.96 mm in diameter) showed greater knock-down activity (>98%) than the smaller ones (0.48 mm, 62.5% in average) to the back panel in the chamber. On the other hand, solvent system significantly affected the residual activity, as the oil-based and water-based aerosols showed 2.3- and 4.8-fold decrease in KT50 values, respectively, between 1 and 10 min after the spray.
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