One Trap or Two? Detection Probability for a Light Clothes Moth Infestation in a Wool Store

Pheromone traps are used to detect webbing clothes moth in stored woolens, and the value of the trap is the chance it notices a small infestation before damage spreads. This study models a 12 m2 store room in which a trap draws males from a floor disc of about 8.0 m2, a male inside the disc is caught with probability 0.22 on a flying night, and males fly on 60 percent of nights. Against a light infestation of 12 males, a single trap detects with probability 1.000 within 14 nights and catches an expected 8.7 males — detection at that density is not the problem. The discriminating case is a single founding male: one trap detects him within 14 nights with probability 0.725, while two traps raise this to 0.862 and three traps add nothing further, because floor coverage is already complete. Against three males, one trap reaches 0.979. The originated rule is two traps per small store room, placed apart at low level, replaced every eight weeks at a cost of USD 12 per round; further traps should be justified only in larger or subdivided rooms. This study is simulated, not measured. SIMULATED, NOT MEASURED.