Aerially applied, liquid Bacillus thuringiensis var. Israelensis (H-14) for control of spring Aedes mosquitoes in Michigan.

Liquid B.t.i. (Vectobac 12AS), when mixed with water at a 1:3 ratio and applied by helicopter at a rate of 1.17 liters B.t.i. (4.68 liters mix) per ha, was 99% effective in a small (mass median diameter on dye cards: 178 microns) droplet size but ineffective (65%) in a large (553 microns) droplet against spring Aedes larvae in snowmelt pools. There were about 6 times as many smaller droplets as larger ones impacting the treated pools, which probably explained the difference in effectiveness for the 2 treatment regimes. Results indicate that liquid formulations of B.t.i. could be aerially applied for spring Aedes control at a considerable cost savings and efficiency over aerially applied, granular formulations.