Insects and mites found in flour mills and their importance for human health

“For many stored product pests the data that are related with their importance for human health are few and not fully justified yet. Moreover, there is an urgent need for the development of rapid detection methods of all stored product insects. The role of stored product arthropods in the development of antibiotic resistance should be examined in a more detail, as this type of resistance is a major issue that requires attention. Harmonized efforts should be initiated in different parts of the globe, since currently stored product insects are positively considered as a protein source for food and feed, which is expected to complicate further the risk and hazard evaluation research.”

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Prof. Christos G. Athanassiou – Laboratory of Entomology and Agricultural Zoology, Department of Agriculture, Crop Production and Rural Environment

Most stored product entomologists are aware of the impact of the presence of stored product insects on the commodity, but there are still disproportionally few data on the importance of these pest for human and animal health. In this context, a vast majority of customers’ complaints for durable commodities, such as flour, are linked with the presence of insects or insect fragments in the final product. The question here is: which are the risks and the hazards that are associated with the presence of these contaminants in durable food? In EU, the European Food Safety Authority (EFSA) in 2015 and later the European Commission (2017) underlined the potential of some insect species to be used as protein source. Some of these species that are proposed for this use in EU are common stored product insect species. On the other hand, there are several publications that illustrate the health hazards that are related with stored product insects. The list of these hazards is not short, as the presence of insects in grains, flour and related commodities, seems to be associated with bacteria and fungi, allergens, non-food borne pathogens, and many more. Hence, there are different points of view regarding insect presence in durable products: do we have enough data to justify health hazards?

Chemical contamination and allergens
It is true that the presence of stored product insects in commodities such as flour is likely to leave a certain odor and strongly affect the organoleptic properties of the final commodity. Most importantly, insects produce several chemical contaminants that have been proved to be mutagens and carcinogens. For example, the flour beetles, Tribolium spp., produce quinones, which, apart from their direct effects on the product, may be associated with tumors. In fact, these effects are still likely to occur even when the products are cooked. Mites are also serious agents of durable food contamination, but for most of the chemicals that are produced by stored product insects and mites, there are no data available so far regarding their health importance.

Allergens are the most commonly regarded side effects from the presence of stored product insects and mites, causing different allergic symptoms. While there are many data available for other urban and suburban insect categories, such as cockroaches, again, the data for stored product arthropods are disproportionally few. The consumption of contaminated food may lead to urticaria, facial angioedema, rhinitis and respiration problems. Along with house dust mites, stored product mites can cause serious anaphylactic reactions. The list of the World Health Organization (WHO) for the arthropod species that cause atopic diseases in domestic and occupational environments contains many stored product insects, including psocids (Psocoptera) and stored product mites. For example, the allergen Lep D I has been identified from the common stored product mite Lepidoglyphus destructor.

Allergen production in arthropods occurs in the digestive tract, reproductive organs, and the parenchymal tissues, glands, and muscles. Through these, certain allergens are continuously produced and deposited in the urban environment, and can be present for long periods, even when the insects or mites are not present anymore. The stability of these allergens is enormous, as some can remain “active” for extremely long intervals, which, in some cases, exceeds one year. The Organization and the International Union of Immunological Societies’ (WHO/IUIS) Allergen Nomenclature Sub-Committee has established a list/database that shows that there numerous allergens that may affect human health, produced by Acarus siro, Tyrophagus putrescentiae and other mite species, as well different insect species, such as the psocid Liposcelis bostrychophila and the indian meal moth Plodia interpunctella.

Microorganisms
The presence of stored product insects and mites in the commodity has, first of all, some indirect effects, which are a direct consequence of changes that are able to cause in the stored-product ecosystem. If not controlled properly, insects and mites will seriously contribute to the increase of both temperature and humidity/moisture, resulting in hot spots that can be expanded causing additional qualitative degradation. This is particularly important in the case of stored product beetles and moths, as their population growth and quantitative infestation potential is enormous. Most importantly, these species are able to interact with stored-product fungi, and often aflatoxigenic fungi, especially when moisture content of the product is high, e.g. 14 % or higher for grains. In this regard, insects can mechanically transfer fungi, depending on their feeding mode. Some of the stored product fungi that are found at the post-harvest stages of agricultural commodities, such as species of the genera Aspergillus and Fusarium but also Penicillium and Alternaria, produce serious toxins that can seriously endanger human health, such as deoxynivalenol (DON), trichothecenes, fumonisins, different aflatoxins, ochratoxin, tenuazonic acid and many more. In general, there are numerous paradigms where there is a positive relationship between arthropod presence of mycotoxin content. In fact, the presence of some stored product arthropods promotes population growth of certain fungal species and vice versa and hence, the relationship is purely symbiotic.

Other contaminants that are associated with common stored product insects and mites found in flourmills and related facilities are bacteria. One paradigm is enterococci (Enterobacteriaceae), which have a certain in the development of antibiotic resistance. In US, it was found that species of major stored product insects, such as Tribolium confusum, Tribolium castaneum, Sitophilus zeamais and Trogoderma variabile hosted enterococci species that could transfer their resistance traits though horizontal gene transfer. This is important given that enterococci are not food-borne pathogen and require other means of transfer; thus, insects can serve perfectly for this purpose in the urban environment and food.

Future needs
There are numerous studies that illustrate all the above issues, but for many stored product pests the data that are related with their importance for human health are few and not fully justified yet. Moreover, there is an urgent need for the development of rapid detection methods of all contaminants mentioned above. Among these, allergens seem to be the most commonly regarded subject and it is expected to draw more attention in the near future. The role of stored product arthropods in the development of antibiotic resistance should be examined in a more detail, as this type of resistance is a major issue that requires attention. Furthermore, we need more data on certain stored product pest categories that occur in houses, such as psocids and mites, given that these constitute the so called “emerging pests” in stored product protection. Finally, harmonized efforts should be initiated in different parts of the globe, since currently stored product insects are positively considered as a protein source for food and feed, which is expected to complicate further the aforementioned risk and hazard evaluation research.

We also suggest you to read our previous article titled "The lowest price is never the best price, the cheapest one always the most expensive".

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