Trading Standards Institute Advice

Pest control in a food business: stored product insects

This leaflet is for all food businesses including those involved in food preparation and production, retail premises, catering businesses, restaurants, pubs, cafes, and takeaway and fast-food shops.

What are stored product insects (SPI)?
Stored product insects (SPI), are a range of insects which can infest dry stored food. The SPI that cause most of the problems are small beetles, weevils, silver fish and some moths.

As stored product insects need time to develop to noticeable levels, an infestation is often a sign of poor stock rotation.

The SPI problem
SPI are usually attracted by carbohydrate-based foods, but dried foods such as nuts, pulses and fruits can also be a target. Buying these foods in bulk to be sold in smaller bags over a period of time can be a problem if you do not take precautions.

Many of these insects are only found inside a building. They are capable of surviving with limited moisture and the dry environment of this type of storage may attract an infestation.

Other insects, classed as scavengers, are found outdoors and are able to survive much colder temperatures. They are sometimes found in birds' nests which may have been built in the eaves of buildings, and so the insects may have easy access to the food stored inside.

Larvae, adult insects and mites may cause physical contamination to food stock, and the larvae of moths are capable of causing damage to the stored food.

All insects or fragments of insects can cause a problem. They could just be a nuisance but may prove expensive if they contaminate stock which has to be thrown away.

Beetles can infest a wide range of food products in warehouses, grain stores and retail premises.

The grain beetle and flour beetle are significant food pests. They are common throughout the UK and are found in bakeries and flour mills.

The adults and larvae feed on grain dust and broken kernels. They have been found in barley, corn, breakfast cereals, crackers, flour, millet, oats, rice, rye, wheat and wheat bran, dried fruits, beans, peas, powdered milk, sunflower seeds, spices and even milk chocolate. Some survive on bits of food dropped in cracks and crevices. 

The beetle often gets into food premises in the flour that is delivered. Small numbers can then multiply into large infestations. If they are found in grain, it will all have to be thrown away.

The female lays up to three eggs a day over a period of five to eight months, a total of about 300 to 450 eggs. The fully grown larvae change to pupae, and after a week the adults emerge. The adults live for three years or more.

Ideally, the flour beetle prefers temperatures of about 30°C and will not breed at temperatures below 18°C.

The biscuit beetle can live in extremely dry conditions and in the UK may produce two generations a year.

The confused flour beetle has glands on its abdomen which make chemicals that produce a bad-smelling, sour smell in flour, making it unfit for baking. This chemical may cause cancer in humans.

The saw toothed grain beetle is now common in the UK and can often be found in packaged food. These insects are able to survive the winter months without difficulty, so relatively small numbers of insects can quickly grow into a serious infestation.

Moths can be found in many food products.

The larvae can cause a lot of damage to stored goods through the process of feeding. They can also contaminate food with the waste products they produce from feeding on the outer layers of timber (known as frass). 

Insect webbing can also build up in areas, causing problems.

The warehouse moth is a major pest of not only warehouses but also retail businesses, infesting cereals, fruit, shelled nuts and spices.

The Mediterranean flour moth is a particular problem in mills, bakeries and catering premises.

The Indian meal moth and the rice moth may be brought to the UK in flour, as well as rice and other cereals, or with peanuts, cocoa beans and dried fruit. However, they cannot survive in the UK in cold conditions.

Grain weevils are found in grain stores throughout the UK. They are regularly brought into the UK in grain and cereal products and in vehicles used for carrying and storing grain. Sacks may also be a source of infestation as the insects sometimes live in the seams and weave of the storage bags.

Rice and maize weevils come from tropical and sub-tropical areas. The maize weevil will breed in maize in the field. The rice weevil will only breed in stored grain. Once established, they are then able to infest undamaged stored grain and possibly move on to other products such as dried pasta.

Control methods for all food businesses
To control the problem of SPI successfully, food stores should be built to provide good storage conditions at all times:

  • food stores should be well ventilated and damp-proof, and made of materials that are easy to clean
  • seal cracks and crevices to prevent insects from getting in and also to make internal surfaces easier to clean efficiently
  • keep storage areas very clean and ensure they are included as part of your cleaning schedule
  • keep stored products above floor level and away from the walls and ceiling
  • a gap between each stack will help ventilation and make it easier for you to clean and check for pests
  • throw away old or spilt stock immediately
  • thoroughly clean farm stores before harvest - dry any grain you take into the store to a moisture-content level below 15%, and then keep the temperature below 15°C
  • several insecticides for grain beetle and grain weevil are available that can be applied to the grain as it enters the store - they will protect the grain for several months, as long as you maintain the correct storage conditions 
  • many insects are attracted to pheromones, which are chemicals produced and given out by the insects - there are a number of traps available to help as part of a pest management system
  • always follow a good system of stock rotation

How to deal with an SPI problem in your catering or retail business
If you have an infestation of SPI, you must remove the source of it as soon as possible:

  • throw away infested foods in wrapped, strong plastic bin bags or in sealed containers
  • use a suitable insecticide to treat the cupboards and storage areas
  • thoroughly clean the storage area before restocking it with food
  • insecticide treatments are useful to kill off any insects once you have removed the source of the problem - these should be applied by a capable pest control contractor if possible

More information
You will find further guidance in our other leaflets on this website. Information can also be found on the Food Standards Agency website.

Alternatively, contact your local environmental health service for advice.

Please note
This leaflet is not an authoritative interpretation of the law and is intended only for guidance.

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