these psmall insects that devour pests are introduced by some farmers into their greenhouses, as they are the only alternative to get rid of them. To be effective, it is important that they remain in the crop even when no harmful pests are present. This requires constant monitoring.
The orchard in southern Spain is internationally recognized. The production of fruits and vegetables such as tomatoes, cucumbers or peppers supplies markets in Europe and the United States, but work on these farms is increasingly suffocating due to rising temperatures. Heat, along with humidity, provide an environment conducive to the development of pests.
This problem is even worse in greenhouses. Farmer Manuel Cuadrado, who runs a pepper farm in El Ejido (Almeria), has been facing these obstacles for years, which, on many occasions, do not disappear with the use of pesticides.
That’s why he decided a few years ago to use a biological control method that had already been used successfully in neighboring greenhouses for years: insects that eat the insect pests that hide among their fruits.
“These pests grow faster and faster, become resistant to phytosanitary products and there are no effective solutions. Although he tried to kill them with pesticides, some always remained and reproduced the next day. They were ahead of me. That’s why I tried to remedy using helper insects”, declares Manuel Cuadrado, who has been working as a farmer since he was 15 years old.
Ladybugs, mites or hoverflies as allies
This technique consists of using insects that act as natural predators of other insects or mites that are harmful to crop growth. In this way, they reduce the risk of uncontrolled proliferation and affect the productivity of a crop.
“To carry it out, we must first identify the pest that affects our crop and then know its natural enemy.”, points out Ignacio Morales, doctor in agricultural sciences and researcher at the Crop Protection Unit of the Polytechnic University of Madrid. These beneficial small invertebrates feed on other specific species that pose a threat to agricultural production. “For example, to combat the aphid, which is one of the most common, parasitoid wasps, sirphids (wasp-like flies) or ladybugs can be used.”.
Today, many companies sell these products made from living organisms. These are marketed at different stages of insect development (egg, nymph, larva, pupa or adult) for different reasons. The first depends on its resistance to factors such as transport, temperatures, etc.
“Usually resist more in the form of egg or larva”, explains the researcher. But it also depends on the insect’s own behavior,”some, like Chrysoperla Carnea, only feed on aphids when they are in the larval stage and not as adults. However, hoverflies are usually sold either as eggs or as pupae.”, clarifies.
Among the most popular auxiliary insects, the scientist singles out the spider mite Amblyseius swirskii, “which controls thrips (Thysanoptera) and other harmful insects very well. there was also a case known in which Tuta absoluta pests were eliminated in tomato crops using the insect Nesidiocoris tenuis”.
Integrated pest control, an alternative to resistance
This technique is part of the method called Integrated Pest Management (IPM), which was developed in response to the growing use of pesticides and which generated great resistance in pests, making their control difficult.
Another important factor that contributed to the development of the MIP was the evidence growing cost to health and the environment caused by the intensive use of pesticides.
“In traditional agriculture, excessively aggressive preventive treatments were used. For example, before having a plague, a product was applied. This involves using a pesticide without possibly being necessary, which can affect other living things. However, IPM tries to reduce the use of insecticides as much as possible. In fact, to carry out a treatment, you must always have exceeded a pest limit”, says Ramiro González, researcher at the Institute of Environmental Science and Technology (ICTA-UAB).
In short, it’s about carefully considering all the techniques available to combat pests and avoiding the most harmful ones as much as possible. Farmers point out that this is the only alternative for some pests, given the resistance that pesticides caused in previous years.
“For certain pests, like thrips, there are no other effective products because they have become resistant to them. However, natural enemies do not cause this problem, as the predator eats the living thing. With biological control we can prevent pests from becoming stronger”, says Jairo F. Quindós, an agricultural technical engineer and farm manager at a company that produces organically throughout Spain.
A food bank so that insects that devour pests do not leave
To optimize the work of these beneficial insects, farmers must ensure that they remain close to their plants, even when there are no pests. This is how the so-called biological control for conservation works: as some insects only act when they are in the larval stage, they are interested in reaching the adults and laying eggs. Thus, when they turn into larvae, they will again control future enemies.
To achieve this continuous cycle, farmers must provide a food source for their helper insects so they can eat when there is no pest: the called banker plants (bank plants). “Adults generally base their diet on nectar and pollen. Therefore, we must have enough plants in the greenhouse that have a staggered or constant flowering”, indicates Quintos.
The expert points out thatIn Almeria, sea alder (Lobularia maritime) is used a lot, a plant that blooms constantly because it attracts an insect called Orius, which helps to control the thrips plague.”. It is also common to plant sunflowers or lavender.
Strategies to keep beneficial insects close to the crop
Another way to keep the bugs out It consists of installing other plants with pests close to the crop —that do not harm the crop— so that the helpers can feed on them. “I sow cereals like sorghum or wheat in my greenhouse because they have a specific aphid that doesn’t harm my fruits. This way, when I don’t have a pest on my fruits or vegetables, the natural enemy can continue to feed and survive.”, proposes Esther Molina, farmer and owner of a greenhouse in Almeria for over 30 years.
The expert indicates that the aphid is one of the most aggressive pests. “It reproduces very quickly and in just 15 days it can finish the harvest or the sugar in a watermelon. it’s doing a lot of damage”. The idea is that when harmful aphids appear on your vegetables, there are already helpers who roam the greenhouse.
It is also common to plant fennel, “a very attractive plant for lacewings (a predator that feeds on many pests). In addition, they are affected by a specific aphid that does not cause economic damage to production.”, adds Jairo, who promotes this technique on social networks.
Plant flowers for pest-eating insects
“Over time, I noticed that beneficial insects are more attracted to pests than flowers, because they need to lay eggs to feed on the pests when they reach the larvae.”, points out Molina. “For example, hoverflies or lacewings always lay their eggs where there are aphids.”, emphasizes.
With all these techniques, the farmer manages to have watermelon crops for three years without any pests. “Until I stopped applying phytosanitary products, both conventional and organic, and fully implemented this system of permanent biodiversity, I was not so successful.”, he says with relief.
The specialist, who also publishes on social networks, started with traditional agriculture and then switched to so-called organic agriculture: “I wanted to have 100% farming of this type and that’s why I incorporated helper insects”.
However, integrated pest management can be used in any type of agriculture. That’s why science is now looking to develop ever more effective helper insects that reproduce faster and are even resistant to pesticides.
The importance of knowing the insects that devour pests
Experts say that one of the main limitations of this technique is the need to know well the life cycle of insects. It is important to constantly observe the development of auxiliaries, pests and culture, aiming at balance.
Molina recalls that a specific protocol for each insect did not always work for him. “For me, they don’t work by protocol, but by needs’ he points.
In addition, the economic factor also comes into play when using these pest-eating insects: “The insecticide is usually much cheaper, and its use is more defended by farmers for this reason. A state subsidy to promote its use would help its development”, proposes the doctor in agricultural sciences from the UPM.
In turn, Quindós emphasizes: “In the short term it may seem expensive, but if we maintain adequate biodiversity in our crops, the cost is minimized.”.