Models for dispersal of vapors in open and confined spaces: Applications to sex pheromone trapping in a warehouse

Methods are presented for mathematically determining dispersal of a vapor in still air, in turbulent air of zero average velocity, and in turbulent or laminar air currents of constant, nonzero average velocity. The methods are combined with several assumptions about insect behavior to derive an insect attraction model that predicts: (1) In a warehouse a searching insect is likely to be attracted to a calling insect if it comes within an attraction sphere, 0.4–2.5 m in radius. (2) The attraction spaces of typical sex pheromone-baited traps that emit pheromone at rates greater than 0.01 ng/sec extend beyond the boundaries of a 10 × 10 × 10-m warehouse. (3) The searching behavior of an attracted insect is likely to be altered from an extensive to an intensive pattern if it comes within an altered-behavior sphere, 6–60 cm from a calling insect or within 10 m of a trap emitting 0.76 ng/sec. (4) Pheromone does not sink unless it is emitted along with a large amount of a high-vapor pressure solvent. The model is used in support of several hypotheses, including: (1) The effect of an adsorptive surface on the vapor concentration after an extended period of emission is negligible except at positions near the surface. (2) Sex pheromone-baited traps with sources of small dimensions have greater trapping efficiency than otherwise identical traps with sources of large dimensions.