Pest-proof storage structures prevent the infestation of bulk grain

Abstract: Commercial grain storage warehouses for long-term grain storage in northeastern Germany were rendered pest-proof by sealing all visible openings. The project idea was to determine the effect of this measure on the occurrence of infestation in a given grain storage. Each warehouse had a capacity of some 500 to 1900 t. Sealing doors and walls or gaps between walls and roof did not cause significant changes in grain temperatures or relative humidity. Rapid weather changes were rather moderate in better sealed structures, but differences between storage sites were much greater than between sealed and unsealed warehouses. At one site storing a total of 3000 t of wheat an infestation of the Indianmeal moth Plodia interpunctella (Lepidoptera, Pyralidae) was observed in September 2014. Four of five warehouses were found infested with numerous moths but also with various beetles and even neuropteran species (Chrysoperla spp.). Indianmeal moths were also found in funnel traps with sex pheromones around the storage structures. Volatiles above the grain mass and in a down-wind plume outside the unsealed doors were collected with tubes containing activated charcoal and determined by GC-MS. The warehouse found un-infested was the one that had been sealed. A pressure test, however, was not successful which was attributed to remaining openings and cracks in the walls of the building. This finding seems to prove that storage pests can actively be excluded from stored grain by an insect-proof seal. Prerequisite for a sealed or hermetic storage is low grain moisture content, in wheat e.g. max. 13 per cent. Grain must also be stored in boxes remote from outside walls, and windows should be covered to avoid condensation and moisture migration, respectively.