Electrostatic deposition of charged insecticide sprays on electrically isolated insects

Electrostatic charging has been used to improve targeting and efficacy of agricultural sprays for decades. However, the benefits of electrostatic deposition have not been exploited for the control of flying insects in the domestic environment. The work described here demonstrated that electrostatically charged sprays significantly increase deposition onto electrically isolated insects (R>100 GΩ), and that this translated into improvements in bioefficacy in direct spray bioassay experiments. The time taken to knockdown 50% (KD50) of the houseflies was reduced from 2.63 to 1.98 min by increasing the charge-to-mass ratio of the insecticide spray from 2.66×10−5 to 2.16×10−4 C/kg, the difference being statistically significant (p=0.043). This increase in bioefficacy remained during space spray bioassays when living room furniture was present in the test chamber. Here the rate of KD50 was increased from 7.30 to 5.60 min by increasing the charge-to-mass ratio of the insecticide spray from 2.66×10−5 to 2.16×10−4 C/kg, with the difference being statistically significant (p=0.044). Electrodeposition occurred despite electrical isolation of the target insects and consequent absence of a conductive path to earth. Improvements in the bioefficacy of charged insecticides over uncharged equivalents arise through the attraction of charged droplets onto insects in flight and through space charge effects causing improved dispersion of the aerosol in the chamber. Any increase in deposition of the charged aerosol onto walls, ceilings and items of furniture does not counteract the improved bioefficacy.