Stored-product insects in a flour mill: population dynamics and response to fumigation treatments

In a wheat flour mill, seasonal trends in stored-product insect trap capture, relationships between trap captures inside and outside the mill, and between pheromone trap capture and product infestation, and the impact of fumigation on pest populations, were assessed. Mark-recapture was used to evaluate the potential for movement of insects outside the mill into the mill. For Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae) and Trogoderma variabile Ballion (Coleoptera: Dermestidae), pheromone trap captures outside were higher than inside the mill, and when inside and outside trap captures were correlated, both indoor and outdoor trap captures tended to cycle according to a seasonal pattern; fumigations did not consistently influence pheromone trap captures, and in only one instance were they found in product samples. Mark-recapture data indicated that P. interpunctella was capable of entering the building from outside. Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) trap captures, in contrast, tended to be lower outside compared to inside, followed a pattern of sharp decline after fumigation treatment, and then steadily increased (0.002–0.005 beetles/trap/ day) until the next fumigation. This pattern, other than potentially the rate of increase, was not impacted by season and outside trap capture levels. Tribolium castaneum was the primary species infesting the product. The information generated in this study provides some of the information needed to develop improved monitoring and management programs.