Pest control and constraints in flour mills

Abstract

Food factories and especially flour mills are object of severe infestations of pest insects. Mediterranean flour moth Ephestia kuehniella and confused flour beetle Tribolium confusum belong to the prevailing pests causing expensive precautions and control measures to avoid complaints of customers. The occurrence of pest insects is not in accordance with food laws and the expectations of buyers of food. Therefore, the biology and behaviour of these pests, the weaknesses of the construction of the premises as breeding place for the pests, the logistic of the flow of product through the machines and the factory have to be understood in the light of pest management. Despite early warning systems and monitoring, inspection of the incoming raw products for possible infestation and many precautions still infestation regularly and often occurs. The choice of possible control procedures is fairly limited. The few remaining contact insecticides lack thorough penetration into infested cracks and crevices let alone the aspect of resistance of pests toward these chemicals. The loss of methyl bromide as quick acting fumigant for thorough pest control of all stages of pests in 2005 opened a chance for sulfuryl fluoride (SF) as alternative fumigant and application of heat in certain circumstances. Also intensive sanitation and partial use of biological antagonists gained its place in the integrated pest management system. The promising use of SF as one to one replacement of methyl bromide found its limitations in the higher cost of the treatment since slightly higher amounts of gas have to be used to be effective possible together with increasing the temperature within the mill to ensure high percentage of mortality. Recently, the maximum residue value for fluorine in treated commodities was reduced in Europe down to 2 mg/kg. This concerns the treatments of large flour mill buildings with in house flour bins that can hardly all be emptied for the fumigation or sufficiently sealed towards the rest of the mill structure. The impact of the high value of the global warming potential (GWP) of SF in comparison with carbon dioxide (higher than factor 1000) is still under consideration.
Heating of all infested parts and machinery and hiding places of pest insects in walls, ceilings and floors sounds easier than it may be in practice. The laws of physics apply and require partially huge amounts of energy to elevate the temperature of concrete, insulating material or other infested parts of the construction to lethal values.
Flour mills and also some other food processing factories offer attractive conditions for surviving for a group of animals like insects, mites, rodents and birds. This group belongs to typical stored product pests. They accompany man since he started after daily hunting and looking for food to store harvested products for a while to become independent from this daily effort some thousand years ago (Reichmuth 2009). These animals are adjusted to live on fairly dry food and get their necessary water supply either outside the premises (rodents and birds) or by chemically cracking the starch into water and carbon dioxide. Together with shelter against uncomfortable weather, elevated temperature due to the electrical machineries and the milling process and plenty of hiding places behind machinery, flour mills are target of pest infestation. Simply, these factories are paradise for certain pests. The preparation of food on the other side does not allow any living or even dead animals that may end up partially in the packages. Therefore, pest management is a very severe issue and requires plenty of dedication in this branch of industry.