The standardization of air-flow in insect suction traps

The air-flow and its variations in sixteen insect suction traps of five different types have been measured, using regularity of air sample size as the criterion of efficiency. Traps with the air-filtering cone enclosed in a cylinder and using axial flow fans with single-phase capacitor-start-and-run or three-phase motors are most efficient and can have normal working limits of +/- 4 % of the mean air delivery. However, for smaller traps which are to be used only close to the ground or in cover, the original type with exposed cone and shaded-pole motor is quite satisfactory provided certain precautions are taken. Normal working limits of +/- 8 % are then obtained. These errors are derived in detail and the expected errors in more extreme conditions and with other traps are indicated.