Mites and dustlice can multiply in products with increased water content and further accelerate the formation of hot spots with increased temperatures. Frass, faeces and the webbings of moth larvae reduce grain convection and keep moisture and heat in the vicinity. Microbial deterioration starts with xerophilic (draught-tolerant) fungi that also require respiration for metabolism. Only at water activity levels close to 1 and corresponding grain moisture contents above 18 per cent will yeasts grow without the need of oxygen. Gases produced by microbials can form flammable mixtures and ignite spontaneously. But even if no fire occurs, mycotoxins produced in heavily infested grain render the formerly valuable stored product a toxic waste.

Where do the pests come from?

If a pest is found in a package, a storage site or a food factory, it may either have been introduced together with the raw product, it may have been present as part of a residual infestation in machinery or hiding spaces in the building or it may have entered through openings being attracted from outside.