Drying-out: Most food pests can survive during fairly dry conditions. This applies to both flour moths and rice weevils. When they have enough to eat, they can live by just 1% RH. Drying will however even for these pests be a stress factor that may increase the effect of simultaneously applied chemical control agents. Xeric insects can be killed by drying-out when you also dust with diatomatic earth. It is the fossilised remains of small diatoms. The fine, sharp particles in the powder scratch the insects’ protective wax layer, and when they lose water too quickly, they die. Against established granary weevil infestation in stored grain, diatomatic earth will not be the first choice because the larvae are securely protected in the kernels. For beetles and moths living freely between the kernels, the method provides good results.
Mites, booklice, plaster beetles and brown house moths are dependent on a damp environment and are easiest fought by drying-out the premises and goods. Chemical control of these animals will rarely be useful for long if the humidity is not simultaneously reduced.
Cooling: The cooler food is stored, the less the risk that there may develop pests in them. At very low temperatures, e.g. -20 ° C for one week, one will usually have killed all stages of all kinds of pests. Many pests can survive freezing temperatures for some time. This applies especially to those pests, which also overwinters outdoors. Species that actually belong further south, such as cigarette beetles, are so sensitive to cold that they do not tolerate refrigerator temperatures below 4 ° C. For regular extermination deep freezing is a rather expensive solution, but for small batches, such as herbal substances, freezing is very suitable.
Mites are generally not sensitive to cold. Many species reproduce well at 4 ° C and are killed only after prolonged freezing. Beetles in food rarely multiply when the temperature is below 12 – 15 ° C. Cooling of products, however, is always an advantage. Even if you do not get temperatures cold enough for reproduction to stop, the life processes take place more slowly and you win some time so the product can be processed or eaten before it goes bad. On the other hand, it is worth remembering that in a refrigerated product poisons practically do not work on insects or mites, so cooling can thus eliminate the effect of a simultaneously applied chemical control agent.
Heat treatment: All stages of insects and mites that are discussed in this book will be killed by a 30-minute stay in 55 ° C warm and dry air. At 50 ° C, it should take about an hour. Heating of the products that can tolerate it, may thus be an effective control measure. In practice, however, it is harder than you might imagine achieving these temperatures generally in a building, which of course is the prerequisite for the method to work. Heat is a stress factor that can amplify the effect of chemical insecticides.
Heating rooms can be a non-toxic alternative to fumigation. Here one must maintain a temperature of 50 ° C for at least 12 hours in order to be assured of a reasonable effect. Please note that pests will try to move away from the heat and try to hide in cooler cracks or simply run away if they can find a way out. Heating a single infected machine that may be difficult to disassemble can often be carried out under an insulating cover while working elsewhere in the room.
Suffocation: Insects can survive remarkably long without oxygen – some even up to 8 days – but in the long run they will need oxygen. This fact is used in airtight silos, the so-called gastight silos, where the carbon dioxide added or developed reduces the insects’ ability to survive the low oxygen content. Insects can also be deprived of their access to oxygen using oils or fats, but this method only makes sense in relation to food, where these substances are nevertheless added. In connection with low oxygen content one must generally count on a decrease in the effect of chemical control agents. A toxic gas, as phosphoresced hydrogen gas, does not work on insects, which are in an oxygen-free pocket during gassing.
Mechanical destruction: Many pest problems will come to an end eventually because the goods at some point are to be ground, pressed or otherwise processed so that any pests are killed. There are machines on the market that by heavy spinning kills insects and mites in grain. Flour can be treated in such an “entoleter” to ensure that it is free of intact eggs and other living things within the packaging. Stirring and transportation of grain, for example, from one silo to another, has beneficial effects because the zones with high temperature are removed, but also because the physical handling of goods directly kills many pests. A free fall of as little as few centimetres kills a certain percentage of the pests, but few products can withstand the mechanical stresses that are necessary to kill all the pests. Insects and mites tolerate surprisingly many bruises. For the sake of completeness we should probably mention that fly-swatters are fine, but of course you cannot use it for anything other than to keep the worst bugs away.
Radioactive contamination: Ionizing radiation, such as for example. X-ray and gamma radiation, produce physical and chemical changes in living cells. The effect depends on the dose and the cell type and condition, and thus what kind of organism is subjected to radiation. Mammals are generally about 100 times more sensitive than insects and mites. Ionizing radiation can affect insects and mites in three different ways: A slight dose will increase the number of mutations, a somewhat stronger dose will sterilize and a really strong dose will be deadly.
In practice, you will usually use gamma radiation from a cobalt-60 source. By radiation of grain or other goods at a dose of 100 Krad one can achieve full extermination of all pests in goods within a week. In practice, however, one can manage with very small doses. A dose of between 10 and 20 Krad will only kill a small part of the population, but the rest will within a week or two become sterile. This can be an advantage because the irradiated and sterile males for a period to some extent protect the goods against new infestations by mating with any newcomer females. The females that mate with sterile males will not get offspring that is capable of reproducing.
Some use this method for the treatment of grain, but it can hardly be price-competitive compared to fumigation.
Single-celled micro-organisms are often less sensitive to radiation of this kind compared to insects and mites. The doses used for the actual radiation-sterilisation of food and equipment will also kill all stages of the pests.
Light traps: Many insects seek towards light. It is particularly light with wavelengths around the ultraviolet part of the spectrum that is attractive to them. Different light traps work in different ways: The light can come from bulbs or fluorescent lamps, and the catch mechanism may consist of either a mesh basket or bag in which the insects are sucked into using a fan or a grill of wires with high electrical voltage.
Light traps are generally very effective against wasps, and if properly positioned they can keep bakeries and fruit shops practically free from these pests. Also moths, blowflies, many small species of flies and mosquitoes are caught fairly effectively with light traps. Light traps have been a disappointment when it comes to common house flies.
Light traps in food industries are not a guarantee against pests, but when strategically set up with a sluice system in doorways, they can reduce the risk of insects flying in from outside. Light traps should be inspected frequently, and can also provide a clue as to which animals currently operate in the premises.
Outdoor light traps will attract more insects to the area than they kill, and among them you will kill, most will be harmless.
Sticky traps: Paper strips with glue and possibly honey are a good, old way to catch flies in the kitchen.
Today these sticky traps are designed in various ingenious ways and are sometimes added attractants (pheromones). However, they are not more effective than the well-known spiral traps.
Sticky traps can alleviate a fly infestation in kitchens and in smaller stores, but in most food companies they will probably be seen as outdated. Sticky traps for cockroaches are designed as small cardboard boxes with entrance holes and glue in the bottom. They will not exterminate a cockroach population, but they can help to keep the number down, and they can show where and in what numbers they exist on the premises. Sticky traps for rats and mice in the form of sheets smeared with a very strong adhesive are marketed in the United States. The method is unlikely to be accepted by many European countries.
Appealing and deterrent fragrances and flavours: Many insects react to certain fragrances by moving towards the source or by being repelled by it. It is also certain flavours that determine whether insects begin to eat or if something is rejected by them.
Fragrances that are appealing to pests are called attractants. Deterrent fragrances are called repellents.
Pheromone is the name for a special type of fragrances emitted by the animals, which triggers a particular behaviour within the species. The best known pheromones are sexual pheromones, fragrances emitted by the one or both sexes to attract the opposite sex.
Attractants in the form of synthetic sexual pheromones can be used to attract insects to traps and to make insecticides more attractive and thus more effective. For proper control of storage pests, fragrances are not sufficient, but they are in many cases useful for monitoring pests. They are often used in traps for various moths and sexual pheromones are also used in cockroach traps. The sexual pheromones, Muscalure, are added to certain poisons of the type which the flies must eat. Repellents are mainly used to protect humans (mosquito oils) and livestock. They are not used for protecting food.
Scare sounds: Scare sounds have in some cases been used to keep birds away from fruit orchards, etc., but never with particularly good results.
In recent years, ultrasound machines have penetrated the market.
They emit sounds with variations from 18 KHz to 40 KHz that is what most people perceive. The theory is that ultrasounds and high volume is a nuisance to rats and mice and certain other pests, and it drives them away. Neither experiments in the laboratory or in practice, however, have noted any effect of these devices.
Some of these devices run with volumes of up to 130 dB, which is far above what is considered harmful to the human ear.
Biological control, in which pests’ natural enemies are exploited, is not a method used against storage pests. There is no doubt that predators and parasites in some cases help to keep storage pests down. Possibly, natural enemies can be exploited more efficiently than we do today. However, the problem is that the requirement will often be a rapid and complete control, while the natural enemies usually only are able to keep pest populations below a certain level.