Optimal Spacing of Pheromone Traps for Monitoring the Tobacco Moth, Ephestiaelutella (Hübner) (Lepidoptera: Phyralidae), in Tobacco Warehouses

Pheromone traps have been widely used for monitoring insect pests in tobacco factories and warehouses. Generally, these traps are placed 10-20 m apart, although a precise scientific rationale for this practice is not available. We examined the effect of trap density on the recovery and localization of tobacco moths released in a 42.3 × 36.5 × 4.0 m tobacco warehouse compartment (1540 m²). In single-trap experiments (0.06 traps/100m²), 15-51% (33% on average) of the released male moths were captured. The capture ratio was not correlated with the distance between the trap and the release point; the highest catch rate was attained when a trap was placed at the most distant position: 47 m from the release point. Capture data from experiments using groups of 4-23 traps revealed that the highest catch rates were always attained by the trap nearest the release point when more than eight traps (0.5 traps/100 m²) were set. These results indicate that the number of traps required for monitoring purposes should be changed - one trap is sufficient for detecting the presence or absence of infestation in a 1540 m² warehouse compartment (0.06 traps/100 m²); more than eight traps (0.5 traps/100 m²) should be set for localization, allowing the location of the infestation to be inferred from the trap with the highest catch rate.