Ordering

Insects found in stored agricultural products and food are classified into different classes. The main species of insects belong to the order Coleoptera and Lepidoptera, but there are also species of the order Diptera, Psocoptera etc. In the broadest sense of the word, storage insects are also cockroaches (Blattaria) or “fish” (Thysanura). Hymenoptera and Hemiptera, as predators or parasites of other species, can also often be found in places that host food. In addition, in the stored food there are many species of mites, mainly of the order Astigmata but also Prostigmata, Mesostigmata etc. Finally, important animal enemies of warehouses are rodents, which are mentioned in another section of the Guide. Below we will mention only the two most important classes, the Coleoptera and the Lepidoptera.

Biology

The ecosystem of the warehouse is very complex, as it is a unique “closed” ecosystem, which has been created exclusively by man (man-made) and is not affected by the external environment (temperature, sunshine, etc.) to the extent that it occurs with other related systems (eg greenhouses). Thus, insects (as well as other animal enemies), in most cases, have adapted their biology to the characteristics of each space that hosts each habitat. Characteristic of these insects is their ability to “travel” long distances (insect travelers) with the same means by which food travels, via land, sea and air. For this reason, the main warehouse insects are now widespread worldwide. Although evolutionarily, these insects have been field insects in the past, many of which are found almost exclusively indoors and, therefore, are also related to Public Health (see below). Both Coleoptera and Lepidoptera are full-bodied, while as a boom, only Coleoptera feed.

Most species found in stored food follow a specific ecological sequence, which is determined to the greatest extent by the type and condition of the product. Thus, the infestation often starts with the so-called “primary” species (primary colonizers) which are able to easily infect whole product, such as grain seeds and other related “solid” products (pasta, etc.). Several species are classified here, such as Sitophilus oryzae, S. granarius, S. zeamais (Coleoptera: Curculionidae), Rhyzopertha dominica (Coleoptera: Bostrychidae) and Sitotroga cerealella (Lepidoptera: Gelechiidae), Acanthoscelch obus. (Coleoptera: Bruchidae). For these species, the larvae develop inside the seeds and the infestation develops without being seen. Secondary colonizers are those that grow on already infected products (eg infected seeds from primary species) or processed products (eg flour, bran, etc.). For these species, the larvae grow on the outside of the products. Most warehouse insects belong to this category. Indicatively, the species Tribolium castaneum, T. confusum, Tenebrio molitor, Palorus spp., Latheticus oryzae (Coleoptera: Tenebrionidae), Ephestia elutella, E. kuehniella, E. cautella, Plodia interpunctella, Pyralis farinale (Lepidopaella): (Lepidoptera: Tineidae), Oryzaephilus surinamensis, O. mercator, Ahasverus advena (Coleoptera: Silvanidae) and Cryptolestes spp. (Coleoptera: Laemophloeidae).

These species grow rapidly in large populations while some have a particularly large cycle of food preferences. For example, P. interpunctella is found in flour as well as in herbal collections, chocolate, legumes and nuts. Similarly, the so-called “tobacco beetle”, Lasioderma serricorne (Coleoptera: Anobiidae), although the most important entomological enemy of stored tobacco, is found in flour, bran, chocolate, spices, dried fruits, pasta, etc. In contrast, some species, such as Carpophilus hemipterus (Coleoptera: Nitidulidae), have a shorter food cycle, such as dried fruit. Then another category of insects, generally called fungus feeders, plays an important role. Many species belong here, most importantly the species of the families Cryptophagidae and Mycetophagidae. The presence of these species is directly related to the decomposition and degradation of the product and their finding in places that host food betrays poor hygiene conditions. Generally, these species do not grow on the product itself but on fungal spores and textures that grow on it. The last stage of the ecological succession are the “scavengers” which cause the further quantitative impairment and qualitative degradation of the product. This includes the species of the family Dermestidae but also the fungi. Also worth mentioning are many species of the genera Attagenus, Trogoderma, Anthrenus and Dermestes, which feed easily on materials of animal origin.

In addition, a class of insects are predators and parasites, which belong to the Hemiptera and Hymenoptera. These should be considered “beneficial” because they feed on other species present in the product. However, the addition of beneficial species to the area and the product does not have the same significance as the corresponding use of beneficial plant protection products, given that it is essentially the addition of other insects to food. Therefore, the biological control of insects of stored products with predators and parasites should be considered with special care. The same applies to the addition of preparations of pathogenic insects, such as insect pathogenic fungi.

Finally, it should be noted that there is a last category of insects, the so-called “visitor insects” which are often found indoors, but are not related to the product. Their presence in warehouses and related areas is therefore random and any decision to take control measures should be decided based on the seriousness of their presence. These are mainly large Coleoptera but also Orthoptera such as Gryllidae.

Curculionidae

This includes species of the genus Sitophilus. Sitophilus grows primarily on whole grains, such as wheat, maize and rice, but more rarely on legumes. They are also often found in packaged foods, such as peeled rice and pasta. Only the blossoms are visible, while the imperfect stages develop inside the seeds, without the infestation being visible. Indicatively, it is stated that until the emergence of the blossoms, the larvae can internally reduce the weight of the infected seeds by more than 50%.

Bostrychidae

This is a family of wood-eating species. However, one species, Ryzopertha dominica, is one of the most important enemies of stored cereals worldwide. It is favored by high temperatures, while it can infect seeds that have a low moisture content (even 8%). The female lays eggs on the outside of the seed and the larva enters it causing severe damage. In addition to attacking stored products, this species has the ability to easily pierce various packages, such as polyethylene and polypropylene.

Laemophloeidae and Silvanidae

This includes the species Cryptolestes and Oryzaephilus, respectively. They are found in starchy products, but also in dried fruits. These are secondary species, ie they are usually found in already infected or processed products and that is why their larvae are located on the outside of the products. It should be noted, however, that many species are able to feed on the “soft” parts of the seed, ie the embryo, with great ease. They also prefer products and places with high humidity.

Tenebrionidae

This includes a large number of species, mainly species of the genus Tribolium. These species are mainly found in starchy products, such as flour and bran, but also in cereal seeds. They develop rapidly important populations and are highly resistant to many categories of insecticides with different modes of action.

Bruchidae

The so-called “loops” are insects that are found exclusively in stored legumes. In fact, each type of legume is affected by a different loop. For example, A.obtectus is found only in beans and soybeans, Bruchus lentis in lentils and B. pisorum in peas. As primary insects, they infect the seeds from the inside. In many of the Bruchidae the infestation starts from the field, just before the harvest, and for this reason it is recommended to treat with insecticides in the pre-harvest stage.

Dermestidae

Dermestidae include species that feed on materials of animal origin, such as species of the genera Anthrenus and Dermestes. Their presence in warehouses is associated with the simultaneous presence of other species. They affect leathers, carpets, wool but also paintings, entomological collections etc. The infestation is carried out exclusively by the larvae. However, this family also includes species that are herbivorous, ie they feed on stored materials of plant origin, such as species of the genera Trogoderma and Attagenus.

Health Significance

Due to the relationship of these insects with food, but also with the places that host them, it is clear that their presence is directly related to Public Health. Their presence has direct effects on humans but also chronic and cumulative action. In general, the effects on Public Health can be divided into four categories.

A first category of animal enemies are those that cause asthma, dermatitis and rhinitis in humans. For example, Dermestidae larvae have hairs that can cause severe dermatitis, blisters and itching. Likewise, cockroaches, after dust mites, are a major cause of asthma.

A second category is species that can carry dangerous organisms into products, such as fungi, which produce aflatoxins, or enterococci, but also other bacteria that are important to human health. Here, many species of Coleoptera (eg Tenebrionidae) but also mites or Psocoptera, seem to be able to “contaminate” the product with other organisms which will cause, depending on the case, liver damage, diarrhea, etc. .

A third category is the intake of insects (and other animal enemies) with food. Although the intake of insects, ie body particles and their derivatives with food seems to be a common phenomenon, however, it is not always associated with harm to human health. Since most of the species mentioned above grow inside the product, the insects themselves, the garments, the droppings and their secretions often end up in the food, through processing. The most common symptoms are vomiting, diarrhea and indigestion but also allergies, spastic colitis, etc.

Finally, one last category is species that produce the same toxins. For example, some of the Tenebrionidae found in flour, pasta and bran produce the so-called quinones (benzoquinones), which can cause dermatitis, erythema, blurred vision and more. Even more important, however, is the fact that quinones appear to be associated with carcinogenesis and are currently classified as “broad-spectrum” toxic substances. Note that quinones react directly with certain substances in food, such as proteins, making them difficult to even detect.

Management Ways

Prevention: By prevention we mean the set of measures that must be taken to prevent the entry of insects into the space and the product. Apart from the processing and storage areas, we should not forget that the houses are also small food processing and storage units. Therefore, the condition of the space and the product should be such as to prevent infestation. Significant interventions can take place at this level, such as so-called “hermetic” storage.

Monitoring: There are two sampling techniques. The first, called “absolute” sampling, is based on product sampling, using a variety of methods (often using a sampler). In this case, the number of insects is reduced per unit of product. The second, the so-called “relative” sampling, is based on various trapping devices, which may have some attractive, pheromone or not. In general, the traps used in stored agricultural products and food vary depending on the use, from “probe and pitfalltraps” traps used unattractive to hanging pheromone-containing adhesive traps. In this case, the traps are checked at regular intervals and depending on the arrests, it is decided to take control measures.

Management: There are various ways to deal with insect repositories, with the main, even today, chemical control. Chemical control is based on two broad categories of insecticides, contact insecticides and fumigants or gaseous insecticides. The former are applied to the premises, usually by spraying, while some are approved for direct application to the product (eg. cereals). Most of them are neurotoxic, ie they act on the nervous system through contact or through ingestion (stomach). Gaseous insecticides, on the other hand, act through the breath of insects. These include phosphine, which is the most important insecticide in the category of fumigants with widespread use in cereals and other products.

Today, the development of other methods is considered imperative, due to the development of resistance by many insects but also due to the adverse effects of chemical insecticides on health. Thus, in recent decades, various alternative methods have been developed. These include the applications of various gases such as carbon dioxide and nitrogen. Other gases, such as sulfuryl fluoride, ozone and propylene oxide, have also been successfully evaluated.

In general, in addition to the very toxicity of the above gases, the death of insects also results from the reduction of oxygen (usually below 3%).

Another promising method is the use of pheromones to disrupt the biology of insects in order to reduce their population.

Extreme temperatures and especially the so-called “thermal disinfestation” are today one of the most important methods for dealing with insect warehouses in food processing areas. Finally, the application of vacuum, infrared radiation and the use of packaging that does not favor the growth of insects, also have important prospects for the immediate future.