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Insects that protect the city

  • City Model
  • Sustainability

Insects, which often go unnoticed or have a poor reputation, play an essential role in self-regulating urban ecosystems.

Cities are increasingly focusing on certain species to control pests, activate pollination, and promote biodiversity.

Una abeja polinizando en las praderas del parque

 

When we talk about biodiversity, we think of natural spaces and wildlife, but rarely insects. In reality, these small invertebrates are essential for the health of all our ecosystems, including urban ones.

Certain beneficial insect species have proven to be great allies of urban sustainability. These small animals have an increasingly larger role in the planning of new green areas and public spaces. Indeed, insects can play a dual role in the environmental health of cities. On the one hand, some species, including the eye-catching ladybugs and certain beetles, are a sustainable alternative to pest control chemicals that are harmful to the environment. Insects such as bees, bumblebees and butterflies are directly involved in the pollination of 75% of cultivated plant species. It should not be forgotten that insects are the primary source of food for many animals, especially the birds that populate our parks and streets.

 

ricino planta

 

Parks, gardens and nurseries, as well as vegetation on balconies, hard shoulders and open fields are the primary refuge for these tiny living beings in urban areas. A habitat that, a priori, may seem hostile to them, but really is not because the use of plant protection products and pesticides is more restricted in cities. Indeed, a recent study published in the journal Nature Communications by scientists from the German Centre for Biodiversity Research (iDiv) concludes that the most successfully pollinated plants are in cities, where insects visit flowers more frequently than in rural areas, given the large variety of plant species and good nesting opportunities.

Owing to its beneficial effects on the environment, experts are calling for these small living beings to be taken into account when planning new parks. The size of green areas, as well as their management, selection of species and distance to other green spaces can be decisive for these animals.

In this sense, the scientific community advises a less intensive management of green areas, less mowing, more flower rich meadows and less manicured lawns, which are less useful for insects, and increased use of native and resistant plant species.

The Royal Botanical Garden (CSIC) highlights that connectivity between green areas in Madrid allows insects to move around easily and access the city centre, for instance, from the El Pardo Forest or the Sureste Regional Park, through the Dehesa de la Villa or the Manzanares Linear Park. According to this institution, the best environments for insects are forest parks on the outskirts of the city, such as El Pardo Forest, Casa de Campo or Soto de Viñuelas. However, there are also places in the city centre which, despite their smaller surface area, also play a role, including parks and gardens such as the Royal Botanical Garden or the Retiro Park, or vegetable gardens.

 

Biological control: insects versus insects

Biological control (also known as integrated biological control or protection) consists of combating certain pests using other insect species that are their natural enemies. When faced with an overpopulation of harmful insects, this sustainable system allows the ecosystem to find its balance releasing other indigenous species that help control pests.

The Estufas Nursery, at the historical Retiro Park, is a pioneer in integrated biological control strategies that were first applied in 2006, building on the experience of Paris nurseries. Javier Spalla, head of this municipal nursery, points out that the most common pests in Madrid are aphids and mealy-bugs. The experts at the nursery carry out several controlled releases each year of what they call “auxiliary insects” that feed on harmful insect species.

 

Liberación del escarabajo Cryptolaemus montrouzieri

The method consists of releasing insects that are already naturally present in the environment based on a strategy that Spalla calls “augmentative fight”. They never use non-indigenous species. He underlines that “it is imperative to understand that the pest species should not be completely suppressed. It is a matter of finding a beneficial balance”.

Allied insect species include the Chrysoperla carnea, a stylish “green bug” with large wings that feeds on aphids, something that certain wasp and lady beetle species also do. Meanwhile, the little beetle called Cryptolaemus is an effective predator of mealy-bugs. Another beneficial insect is the Anthocoris nemoralis or “pirate bug”, which protects laurel and pear trees.

 

More resistant plants and “reservoir plants”

Current regulations have drastically reduced the use of plant protection products and chemical pesticides. Spalla clarifies that “these strategies are being applied in Madrid’s parks, although self-regulation is clearly the trend today”. “New urban developments take all this into account,” he added “by planting more resistant, native species and designing more sustainable gardens”.

The Retiro Park’s municipal nursery cultivates seasonal flowering plants, perennials, and ornamental indoor and outdoor plants to identify the varieties best adapted to Madrid’s climate and pests. “The choice of plant species with fewer pest problems plays a major role in the biological control strategy,” said Spalla.

This expert pointed out that it is possible to attract beneficial insects “without the need to release them and run the risk of losing them”. You need only to plant so-called “reservoir plants” in the gardens, together with the rest of the plant species. Beneficial insects are specially attracted by the pollen of these aromatic plants. The insects establish themselves in the plant “using them as refuge and alternative food source”, said Spalla. These natural habitats include “certain flowering plants, castor beans, marigolds and fennel that attract ladybugs and others” added the municipal officer.

 

An insect sanctuary in Milan

A good example of a new park designed for and managed with beneficial insects is the Biblioteca degli Alberi (BAM) or Library of Trees, a large green space between skyscrapers, next to the Porta Garibaldi train station, at the heart of the great urban regeneration project at Porta Nuova (Milan). The BAM Park is an open-access botanical garden with a vibrant cultural program that connects the surrounding streets. The park is characterised by a wide variety of plant species distributed across twenty circular forests and linear paths that form irregularly shaped fields.

 

El parque BAM de Milán, frente al Bosco Verticale, edificio emblemático del proyecto urbanístico Porta Nuova.

 

Petra Blaisse, founder of the Dutch studio Inside Outside, who designed this green space, hopes that its proper maintenance and use will contribute to “attract insects, birds, frogs and toads, and even fish and salamanders, if people do not allow their pets inside the pond”. She also anticipates that “the change of seasons will dazzle the public with chirping birds and the sound of bees, bumblebees, grasshoppers and various amphibians”.

Jana Crepon, a landscaper at the same study, is committed to achieving a natural balance in parks and “letting the worms breathe the earth, the ladybugs feed on green flies and the birds and caterpillars fight other pests”. The expert highlights the presence of “clover grass, a plant that blooms almost all year round and attracts many insects” in the BAM park. “There are also lavender and other aromatic, herbaceous insect plants found in France and Italy,” she continued, “while less interesting plants for insects, such as bamboo gardens, provide other habitats and shelter”.

 

Las coloridas mariquitas son utilizadas frecuentemente para el control de plagas.

 

The Fondazione Riccardo Catella, responsible for the upkeep of the BAM Park, attests the success of these design measures. Proof of this is the abundance of two beetle species in the park, the Staphylinidae and the Carabidae, which are considered bioindicators of a healthy and habitable environment. This foundation is implementing various initiatives to enhance the park’s biodiversity further with rose bushes and other less common garden species, such as nettles, which serve as a habitat for insects. All these efforts have resulted in the presence of different varieties of butterflies, ladybugs, bees, ants, dragonflies and many other insects.

Very close to the BAM Park is the so-called Bosco Verticale, an iconic building by the architect Stefano Boeri, whose façades are covered by lush vegetation, complementing the biodiversity of the neighbouring park, while contributing to the presence of beneficial insects. “We created a horizontal forest and he, a vertical one, but they are part of the same landscape,” said Crepon. “This place has become a sort of oasis for the city’s insects,” she concluded.

 

Madrid Nuevo Norte committed to biodiversity

The search for urban biodiversity, a hallmark of Madrid Nuevo Norte and its commitment to the preservation of environmental values, includes harnessing the benefits of insects in the city’s green spaces, as part of its naturalisation strategy. This is complemented by other measures such as greater use of native plant species, reducing mowing frequency, promoting shrub masses and flower meadows, and creating small ponds and seasonal flood zones.

19 January 2021

Author

Distrito Castellana Norte


19 January 2021

for Distrito Castellana Norte