Insects and agriculture

The global tendency to concentrating human population in cities has distanced us from a perception which rural societies have always had: the world is full of insects. However, these abundant, diverse and ubiquitous creatures still play a decisive role in agriculture, not to mention the more or less natural ecosystems.

It is estimated that the number of insects which live simultaneously on the planet is around 10,000,000,000,000,000,000, that is, 10¹⁹ individuals. A figure which it is impossible to understand in its exact dimension. But in addition, arthropods represent about 90 per cent of the diversity of known species of animals (and most of these are insects). We are talking of over a million species of insects, but this figure refers only to the ones we know. Two of every three species of animals are insects; and it is believed that for every human, there are 300 million individual insects. Furthermore, insects can be found in all environments, land, water and air, and, with the exception of the marine environment where there are few species of insects, and the polar regions, insects are found high altitudes and depths in the edaphic and cave environments, from the Equator to parts of Greenland and Antarctica.

As regards human activities, insects are extremely important, although public opinion is dominated by the prejudice they are a prejudice if you will pardon the play on words. In economic terms, their value is very high. For example, in agriculture for every euro produced by a crop of apples, 92 cents come from the pollination service of insects, between 80 and 99 cents for cranberries, 78 cents for kiwis and nearly 50 cents for strawberries, and they represent 2,400 million euros in associated value for Spanish agriculture, according to data from the FAO (Food and Agriculture Organisation). On the other hand, insects are a strategic reserve of proteins for human consumption as entomophagy completes the diet of around two thousand million people, and this will increase in the future.

Insects are undoubtedly important as vectors for disease, some with a huge impact like malaria, dengue and yellow fever; or as competitors for agricultural or forest products (plagues). But the proportion of species that cause problems to human beings is tiny, no more than 2%, although they destroy 15% of crops, when compared with the pollination services to the ecosystem, pest control, and support for the land trophic chain, breaking down waste products etc. This etcetera includes human activities like beekeeping, sericulture, or producing cochineals (mealy bugs) and food for poultry.

Insects also play an important cultural role and therefore deserve our consideration and conservation. Thus, they are part of popular traditions and many elements of culture all over the planet, from European fables to Chinese or Mayan mythology, many linked to the rural world of farming or shepherding.

It is beginning to be commonplace for the diversity of insects to decrease everywhere, and in general terms this is an irrefutable fact. Spain is no exception, but rather, the depressing paradigm. There are many factors behind this decline in the insect population, impoverishing diversity and even wiping out species. The global change in this case is evident from the dispersion of invading species, competitors with an advantage over local fauna, the use of pesticides, herbicides and other poisons, intensifying of crops, with the consequent regression of traditional farming methods, the exploitation of large tracts of forest and grasslands, until recently free of such aggressive agricultural and pastoral techniques, generally for monoculture (single crops) of soya, maize and palm, or for the totally unsustainable rearing of cattle.

The picture with illustrates this article shows a Xylocopa violacea, a «carpenter bee» —as they are commonly known— which pollinates many wild and cultivated species, and is particularly attracted to leguminous plants, although it pollinates generally. In kitchen gardens they are efficient pollinators of the aubergine and tomato plants, and other vegetables, and regularly visit gardens with wisteria (Wisteria sinensis).

Carpenter bees build their nests inside the wood, in which they carve out tunnels, vibrating their bodies while they scratch with their jaws. Each nest has only one entrance, although it may be connected to several adjoining tunnels. The tube (tunnel) acts as a nest for its young and as storage for food.

Let us hope that the image of this solitary bee stirs our interest in the beneficial role of pollinating insects.

José Luis Viejo Montesinos is Professor of Zoology at the Biology Department of the Universidad Autónoma de Madrid (Spain). His specialist field is Entomology, in which he has been working for forty years in diversity, ecology and the conservation of Lepidoptera. He teaches many degree subjects in Biology and Environmental Sciences and masters degrees in Biodiversity and Teacher Training for Secondary Education. He is a member of the editorial board of several publishers, such as Graellsia or Shilap, and was Secretary of the Asociación Española de Entomología (Spanish Association of Entomology) from 2001 to 2009 and President of the Real Sociedad Española de Historia Natural (Spanish Royal Society of Natural History) from 2005 to 2010. 

On his part, Juan Carlos del Villar, whose photograph illustrates this Work of the month, is a prominent member of Fotógrafos de la Naturaleza de Madrid, Fonamad (Photographers of Nature in Madrid, Spain). His photos have been published in different books and magazines, and he has had many exhibitions. His speciality is photographing nature, particularly birds and insects in the Sierra de Guadarrama (Madrid, Spain).