Clara Inés Nicholls is a Colombian agronomist with a Master’s degree in Entomology from the Colegio de Postgraduados, Chapingo, Mexico, and a Ph.D. in Entomology and Biological Control of Insect Pests from the University of California, Davis. She is a professor of Sustainable Rural Development in Latin America at the University of California, Berkeley. She also teaches at Santa Clara University and other universities in Colombia, Brazil, Chile, Argentina, Spain, and Italy. Her research focuses on managing vegetation biodiversity on farms to provide habitat to encourage natural control of insect pests in various agricultural systems. She is the author of four books (including Biodiversity and Pest Management in Agroecosystems) and more than 50 articles in scientific journals.
RAFI Farmer Outreach Manager Carolina Alzate Gouzy spoke with Professor Nicholls about agroecology and natural pest control.
Carolina Alzate Gouzy (CAG): Let’s start by understanding what makes an organism a pest.
Clara Nicholls (CN): An organism is considered a pest when its population reaches a level at which, if no action is taken, the economic cost from the loss in production due to the organism will be greater than the cost of control or treatment. Agroecological practices aim to keep phytophagous insects (insects that feed on plants) at low population levels, causing only minor damage that does not affect economic output. In other words, agroecological practices can keep the insect from becoming a pest.
One question that immediately arises is: How can the density of an insect be reduced so that it is not considered a pest and does not cause economic damage? In conventional agriculture, the response is to apply chemical pesticides, which do reduce the insect population, but at a high environmental cost. They also only work until the pest develops pesticide resistance. In agroecology, we ask the question, “What is the root of the problem that allowed the insect to become a pest?”
CAG: What are some reasons a phytophagous insect becomes a pest?
CN: Generally, pest problems arise in monocultures that provide a large supply of a single crop. Insects that feed on plants respond to olfactory and visual signals. If a field has only corn, it will be very easy for a specialized phytophagous insect to find that crop through sight and smell. But if we combine corn with beans, squash, or other crops, the smells and colors change, and that phytophagous insect cannot find corn as easily.
In addition, diversified farms provide habitat for natural predators and parasites that attack the pests. But in a conventional monoculture, pesticide application tends to eliminate these natural enemies. Another issue is that as long as you use a chemical, you constantly expose the insects to the same stimulus so the population can develop resistance. The same thing happens with genetic engineering and GMOs. In summary, farmers who rely on monocultures, pesticides, and GMO crops get trapped in a “pesticide treadmill,” forced to apply more and more pesticides as pests develop resistance and as natural enemies are eliminated.
CAG: How do you address these pests with an agroecological approach?
CN: From an agroecological perspective, the first thing is to prevent phytophagous insects from becoming pests. So, how do we do that? If the root cause of the problem is the monoculture, we act by breaking up the monoculture with diversity. Diversification — through crop rotations, intercropping, or agroforestry systems — makes it more difficult for phytophagous insects to find the host plant and also attracts natural enemies that feed on the phytophagous insects and keep their population under control. The introduction of flowers is key as natural enemies need pollen and nectar for fecundity and reproduction; other plants can serve as “trap crops,” luring pests away from the crop, while others may repel some phytophagous insects that do not like the plant’s smell.
CAG: For example, cilantro and tomato?
CN: Exactly. In that case, the smell of cilantro repels potential pests such as whiteflies from tomatoes.
CAG: What are other ways to attract natural enemies to control pests?
CN: It is important to understand what natural enemies need to thrive and remain in the field. Many parasitoids of pest insects need pollen and nectar for longevity. Not just any flower will do; planting borders or strip rows of flowers that offer exposed pollen, bloom for extended periods, and flower at the same time crops are planted can help ensure the presence of natural enemies during critical periods of the crop’s growth.
Natural enemies also need shelter and nesting sites. Some, like coccinellids (the family of beetles that includes ladybugs), are attracted to herbaceous plants, so leaving a herbaceous layer for them is essential. Ground-walking predators, like spiders, require soil cover in the form of cover crops or mulch. Others, like lacewings, need trees and larger bushes, which can be provided in the form of hedgerows. So, it is vital to know the ecology of natural enemies when designing diversified farms.
In ecology, we always say that the more diverse a natural ecosystem, the more stable it is. In an agroecosystem, you have a crop to protect, so you must work with auxiliary biodiversity that provides benefits for farmers, including pest control.
CAG: How do you visualize and monitor biological pest control in the field to ensure you apply the right strategy?
CN: First, we look at what we have in the field, what the pest is, and how, where, and when it affects the crop. What does the pest feed on: leaves, roots, or fruit? Then, we must understand the pest’s life cycle and when it is most susceptible to predators or parasitoids. For some, when the insect is in the pupal stage, it is generally more difficult for a natural enemy to feed on it, but if a pest is in the egg or larval stage, parasitoids or predators can reach it more easily.
There are many methods to capture and identify the pests and other insects on your farm, including sweep nets, yellow sticky traps, yellow pans, pitfall traps, and direct observation of plants. When farmers observe the diversity and abundance of natural enemies in their fields, they can gain confidence about the potential for natural pest control methods to prevent or reduce their pest problems.
CAG: How can farmers learn more about the insects in their agroecosystem and start implementing biological pest control?
CN: Simple courses and field guides can help farmers identify insects on their farms and understand how biological control works. They can also learn through field visits and experimentation, knowledge exchange with other farmers, and access to clear information.
Training starts on the farm by observing what insects are present and if the farm’s environmental conditions are conducive to biological control. It is important to learn little by little. We work with farmers to collect insects, identifying which are beneficial, which are pests, and which, like decomposers, are neutral but could provide additional benefits in the absence of chemical pesticides. Then we observe if the farm provides habitat (refuge, nesting sites) and alternative food sources (such as flowers) for beneficial insects.
So, if a farmer wants to make an agroecological transition, the first step is eliminating chemical pesticides. But this process involves learning, trust, understanding, and gradually transitioning. The farm doesn’t have to be transformed all at once; farmers can change a small section at a time and observe the differences compared to the rest of the farm. In these experiments, they can observe when natural enemies such as ladybugs and lacewings start coming from the system’s edge to eliminate the pest. Through observation and experimentation, farmers become increasingly confident in agroecology’s ability to activate and sustain ecological processes on their farms.
Carolina Alzate Gouzy joined RAFI in August 2022. She has worked on agroecological projects as a part of non-governmental organizations that seek a more just and regenerative relationship between the rural and urban worlds. She is a biological engineer with a Master’s in Agribusiness and a Ph.D. in Sustainable Development from Universidade de Brasília, Brazil.