A diffuser for distributing spray or insects from an aircraft is mounted on an aircraft and comprises a distribution tube connected to an insect source at a first end and open to the outside at a second end for distribution of the insects. A nozzle surrounds the second end and a tube cover surrounds the second end within the nozzle. The tube cover has an aerofoil, or wing-shaped, cross section. The nozzle shape sets up an air transition volume between the aircraft and ambient air designed for a maximum wind shear over any cubic centimeter volume within the air transition volume to be less than 60 km/h, and therefore allowing distribution of insects such as mosquitoes from the aircraft without damage, or allowing aerosols to be spread as large droplets.