Understand the biological control of mites

There are dust mites everywhere, and we are in contact with them every day, although often without realizing it. They are usually very small, and many are light in color, making them difficult to see. The mites that most scare people in general are those found inside our homes, among the fibers of the carpet, carpet, curtains, bedding, under the bed, etc. Many people suffer greatly from the presence of these, due to respiratory allergy problems caused by them.

Farmers are well aware, however, of another type of mite that causes them a lot of concern. These are mites that feed on plants, often significantly reducing the productivity of various crops. These are pest mites, whose main representatives belong to the families Tetranychidae, Eriophyidae, Tenuipalpidae and Tarsonemidae.

Several important species can be cited within each of these families. One is the two-spotted mite (

, family Tetranychidae), which attacks more than a hundred important plant species, including cotton, beans, papaya, soybeans, tomatoes, etc. They leave the attacked leaves yellow and covered in webs that they produce. The tomato rust mite (

, family Eriophyidae) attacks very few plants in the solanaceae family, being best known for attacking tomato plants, a crop that causes enormous damage in several parts of the country, especially in the driest regions of the Northeast. The attacked leaves first turn dark and shiny, then dry and fall. The citrus leprosy mite (

, family Tenuipalpidae) is the main pest of citrus in the state of São Paulo, but it also attacks several other important crops throughout Brazil. They attack leaves, branches and fruits, but their attack is most pronounced on the fruits, which have rounded brown spots and fall prematurely. The white cotton mite (

, family Tarsonemidae) is one of the smallest mites that cause damage to cultivated plants, being found mainly on the youngest leaves of cotton, papaya, beans, etc. Despite its small size, it causes great damage, precisely because it attacks the regions of the plants that are still growing, causing the leaves to appear deformed at a later stage.

Several other species of pest mites could be mentioned in each of those families, causing greater or lesser damage depending on various factors, such as climatic conditions prevailing each year, variety of plant cultivated, irrigation system used, types of pesticides used for the control of other pests associated with mites, planting time, etc.

Mite control

To prevent damage caused by these mites, farmers generally use chemical products, many of which are considered effective in reducing the population of pest mites shortly after their application. Despite the undesirable side effects of many of these products, in the current cultivation system of many crops, the use of these products represents the only viable way to allow the reduction of certain pest mites. Reducing the use of pesticides, in these cases, is only viable through the adoption of new cultivation systems, which favor the balanced development of the crop and disfavor the development of pest mites.

In several situations, however, alternative control methods exist and have been used to reduce the population of various mites. One of these methods refers to the use of natural enemies, generally bred on a large scale under controlled conditions and released into fields where the pest is present. These releases may be temporary, until the natural enemy (usually exotic to the region) establishes itself in the field and can control the pest indefinitely. In other cases, releases have to be made periodically, in the form of a true biological acaricide.

There are now hundreds of laboratories, especially in North America and Europe, that produce these natural enemies and sell them to farmers. The most widely traded species today

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, for the control of pest mites (specifically for the control of two-spotted mites). These natural enemies are predatory mites that belong to the Phytoseiidae family, and are also known as “phytoseiids”. In addition to these, other phytoseiid mites are used to control thrips in greenhouses:

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. Another species of predatory mite belonging to the Laelapidae family has more recently been used commercially to control fly larvae from the Sciaridae family, serious pests in the soil of greenhouses in Europe; This is the mite known scientifically as

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European researchers have informed us that these predators are increasingly used in greenhouses in Europe to control pest mites, especially due to the considerable problems of pest resistance to currently registered acaricides. In strawberry farming, predatory mites are also frequently used to control the two-spotted mite, both in Europe and the United States. Another possibility is to make use of natural enemies that are already present in the environment, promoting their action through the adoption of cultivation practices that allow greater development and activity of these natural enemies. Many well-recorded cases exist regarding this biological control strategy, which refers to the use of predatory mites that only require a certain “collaboration” from man so that they can perform their role as pest mite controller. What actually happens is that, often, a potentially efficient predator present in the field is disadvantaged by the cultural practices in use, such as the application of non-selective pesticides, which eliminate the population of this predator when they are used for control. of pests.

In general, the “little help” needed corresponds to reducing the volume of pesticides used in the field, by determining the maximum levels of mites that a certain crop can tolerate or by using more specific pesticides, which kill pests but do not affect enemies. natural. This is what is normally called “integrated pest management”.

Importing dust mites

Another type of biological control of pest mites on plants is done with the use of predatory mites that are taken from one country to another, usually to control a species of pest that has been introduced. An example of this control strategy refers to the biological control of the cassava green mite (

) in Africa, through the introduction of its predators collected in Brazil and other South American countries over 17 years. The successful establishment of these predators in around 13 African countries has resulted in considerable savings for farmers, which is now growing year after year, with the permanent action of these predators, without the need for human action.

In practice, what is being done in Brazil in this regard? A lot, but still not enough. Brazil currently has a good number of professionals linked to the area of ​​biological control of mites, but considering the size of the national territory, this number should be higher.

Basic studies have already been carried out for some time, in order to indicate which of the species of natural enemies that occur in Brazil have the greatest potential for use. This requires years of studies, personnel and resources, but the most important thing is making institutions aware of the importance of the subject.

Interested companies

Little by little there is a positive evolution, such as the involvement of the private sector in these activities, either through greater demand from public institutions for studies in this area, or through partial financing of these activities, or, at the other extreme, through the offering of techniques and products to farmers. Regarding the involvement of public institutions, as resources are limited, sectors that present greater demands will tend to benefit more. Seeking to anticipate the occurrence of actions, some companies have proposed to finance the carrying out of work that puts them at the forefront of the use of biological control, whether due to economic reasons, the lack of options, or a conscious option to promote the use of more natural control methods. At the “other end of the line”, small companies are beginning to emerge in Brazil interested in occupying a space that is still open, as producers of natural enemies for commercialization, or offering consultancy in the area of ​​biological control of mites, both in the South and Southeast states. from the country.

The future looks promising, especially if we take into account that every day the size of the population interested in consuming products in which the use of pesticides is absent or reduced to a minimum is growing. Large supermarket chains already offer consumers this option, having separate shelves for this type of product. The current availability of these products on the market will be significantly influenced by the implementation of this alternative control method, through the action of public research bodies and consultancy companies.

Gilberto J. de Moraes

ESALQ / USP