Efficacy of a commercial liquid vaporiser (Transfluthrin 0.88% (w/v)) under various room sizes against Culex quinquefasciatus Say.

Abstract

The standard protocol (WHOPES) efficacy testing on flying insect is under Peet Grady Chamber (PGC) of size 6m 3 in closed condition. However, in the real scenario, the efficacy is bound to vary with the room size, ventilation and mode of activity of the vaporising machine etc. To know the role of room size in the efficacy of vaporisers, efficacy studies were carried out with a commercial liquid vaporiser with Transfluthrin 0.88% w/v as active. The heating device used had two different modes of operation viz., low setting and high setting. At low setting, the liquid is expected to emanate slowly compared to high setting. Evaluation was carried out at different settings under various room size viz., 6 m 3 , 20 m 3 and 40 m 3 and the results are compared. All the experiments were conducted without ventilation, so that all the chamber ports remained closed throughout the experiment. The time required to knock down 50% and 95% of test population (KT50 and KT95), and mortality at 24 hours after exposure were analysed and compared. The results revealed that experiments in 6m 3 at high emanation mode recorded minimum KT50 value (10.61 min.) followed by experiments at high emanation mode in 20m 3 room size (15.06 min.). Evaluation at low emanation mode in PGC recorded faster knock than in higher volume rooms with high emanation rate. Efficacy was found to decrease with the increase in room size which was reflected in increase in KT50 and KT95 values and decrease in mortality at 24 hours of exposure indicating the importance of room volume for the product performance. It is concluded from the present investigation that performance of the products with varying room size should be considered as criteria for efficacy as it reflects the real scenario and to avoid the failure of any household products under field conditions.