From the last module you learned that there are some insects, like bees, that are clearly valuable to farmers in healthy agricultural systems. Agroecology goes a step further and re-thinks even the idea of insects as “pests”. In this module, you’ll explore how agroecology turns pest eradication into pest management, and then finish the module with an even more radical way of interacting with insects on our farms (hint: they’re on our plates!).
Below, you’ll learn how agroecologists think about pest control in agroecosystems.
Excerpt 1: Healthy Soils – Healthy Plants
by Alteri, M. and Nicholls, C. | from Ecologically based pest management: a key pathway to achieving agroecosystem health
The loss of yields due to pests in many crops, despite the substantial increase in the use of pesticides is a symptom of the environmental crisis affecting agriculture (Altieri and Rosset, 1995). It is well known that cultivated plants grown in genetically homogeneous monocultures do not possess the necessary ecological defense mechanisms to tolerate out breaking pest populations. Modern agriculturists have selected crops for high yields and high palatability, making them more susceptible to pests by sacrificing natural resistance for productivity (Robinson, 1996). On the other hand, modern agricultural practices negatively affect natural enemies (predators and parasites), which do not find the necessary environmental resources and opportunities in monocultures to effectively suppress pests (Altieri, 1994).”
A key feature of modern cropping systems is the frequency of soil disturbance regimes, including periodic tillage and pesticide applications, which reduce soil biotic activity and species diversity in agroecosystems. Such soil biodiversity reductions are negative because the recycling of nutrients and proper balance between organic matter, soil organisms and plant diversity are necessary components of a productive and ecologically balanced soil environment (Hendrix et al., 1990). The ability of a crop plant to resist or tolerate pests is tied to optimal physical, chemical and biological properties of soils. Adequate moisture, good soil tilth, moderate pH, right amounts of organic matter and nutrients and a diverse and active community of soil organisms all contribute to plant health. Organic rich soils generally exhibit good soil fertility as well as complex good webs and beneficial organisms that prevent infection by disease causing organisms as Pythium and Rhizoctonia. On the other hand, farming practices that cause nutrition imbalances can lower crop resistance. High nitrogen fertilizer levels can enhance the incidence of diseases such as Phytophtora and Fusarium and stimulate outbreaks of Homopteran insects such as aphids and leafhoppers (Campbell, 1989). In fact there is increasing evidence that crops grown in organic rich and biologically active soils are less susceptible to pest attacks. Many studies suggest that the physiological susceptibility of crops and pathogens may be affected by the form of fertilizer used (organic vs. chemical fertilizer). Studies documenting lower diversity of several insect herbivores in low-input systems, have partly attributed such reduction to a low nitrogen content in organically farmed crops (Magdoff, 1992). In California, a series of comparative experiments conducted on various growing seasons between 1989-1996 where broccoli was subjected to varying fertilization regimes (conventional vs. organic) showed that agroecological techniques can reduce the abundance of key insect pests, cabbage aphid (Brevicoryne brassicae) and flea beetle (Phyllotreta cruciferae), while sustaining yields. Lower herbivore numbers in organically managed plots were attributed to low foliage nitrogen content in compost fed broccoli plants (Altieri, 1994).
In Japan, density of immigrants of the planthopper Sogatella furcifera was significantly lower while the settling rate of female adults and survival rate of immature stages of ensuing generations were lower in organic rice fields. The number of eggs laid by a female of the invading and following generations was smaller, and the percentage of brachypterous females in the next generation was also lower. Consequently, the density of nymphs and adults in the ensuing generations decreased in organically farmed fields (Kajimura, 1995).
In England, conventional winter wheat fields developed a larger infestation of the aphid Metopolophiunt dirhodum than its organic counterpart. This crop also had higher levels of free protein amino acids in its leaves during June, which were believed to have resulted from a nitrogen top dressing of the crop in early April. However, the difference in the aphid infestations between crops was attributed to the aphid’s response to relative proportions of certain non-protein to protein amino acids in the leaves at the time of aphid settling in the crops (Kowalski and Visser,1979). In greenhouse experiments when given a choice of maize grown on organic versus chemically fertilized soils, European corn borer females preferred to significantly lay more eggs in chemically fertilized plants (Phelan et al., 1995).
Nutrition is also important in determining susceptibility or resistance of plants to pathogens. Mineral nutrients are essential metabolic regulators of plant growth, and most studies indicate that nutrition affects pathogens and diseases indirectly. Biological activity in the soil becomes very intense in response to organic amendments and increase fungistasis as well as populations of existing microbial antagonists. Composts of diverse organic materials have proven effective in controlling diseases. Many types of compost host beneficial organisms that feed directly on pathogens, compete with them for nutrients or produce antibiotics (Tjamos et al., 1992)
Balanced soil nutrition helps plants stay more vigorous, increase the growth rate, make better use of soil water, and improve anatomical or histological characteristics. These factors enable plants to produce greater numbers of roots, allowing more surface area for root absorption and nutrient uptake, and possibly, shortening susceptible stages of plant growth. This allows plants to function more efficiently even when some roots are infected. Histological changes strengthen plants and possibly create barriers more difficult for pathogens to breach. A healthier plant may also increase quality of exudates, which can stimulate increases in populations of antagonistic microorganisms. These, in turn, may compete with pathogens for nutrients or possibly produce toxins that directly affect pathogen development and survival (Palti, 1981).
Application of nutrients (especially N) may increase competitive suppression of crops by weeds, as most weeds, (especially C4 species) are often more responsive to application of nitrogen than other crops. A study reported that application of chemical N fertilizer to wild oat-spring wheat mixtures increased wild oat growth and decreased wheat yields. On the other hand other studies have shown that N fertilizer can improve the competitive status of crops. What seems critical in determining the outcome of competitive interactions, is the timing of nutrient availability relative to crop and weed demands upon nutrient supplies (Liebman and Gallandt,1997). Emerging research shows that the species composition and general ecology of weeds is radically different in organic versus conventionally fertilized systems. Yield reductions of wheat due to interference from Italian ryegrass (Lolium multiflorum Lam.) were greater under conventionally fertilized conditions than under organic fertilized conditions. In many cases weed suppression is related to delayed N release from the organic N source compared to nitrate fertilizer. In other cases soil incorporated organic residues increase phytotoxicity or pathogen activity, which suppress weed seed and/or seedlings (Liebman and Ohno, 1998).
Achieving health in agroecosystems requires that management be directed at improving soil and plant quality, as the link between healthy soils and healthy plants is fundamental to EBPM (Ecologically-based Pest Management). Of key importance is also the realization that the level of internal regulation of function in agroecosystems is largely dependent on the level of plant and animal biodiversity present. In agroecosystems, biodiversity performs a variety of ecological services beyond the production of food, including recycling of nutrients and regulation of pest populations. For this reason agroecologists promote multifunctional technologies that enhance biodiversity, as their adoption usually means favorable changes in various components of the farming systems at the same time. For example, legume based crop rotations; one of the simplest forms of biodiversification can simultaneously optimize soil fertility and pest regulation. It is well known that rotations improve yields by the known action of interrupting weed, disease and insect lifecycles. However, they can also have subtle effects such as enhancing the growth and activity of soil biology, including vesicular arbuscular mycorrhizae (VAM), which allow crops to more efficiently use soil nutrients and water, and thus better resist pest attack.
The ultimate goal of agroecological design is to integrate components so that overall biological efficiency is improved, biodiversity is preserved, and the agroecosystem productivity and its self-sustaining capacity is maintained. The goal is to design a quilt of agroecosystems within a landscape unit, each mimicking the structure and function of natural ecosystems, that is, systems that include:
- Vegetative cover as an effective soil- and water-conserving measure, met through the use of no-till practices, mulch farming, and use of cover crops and other appropriate methods.
- Nutrient recycling mechanisms through the use of crop rotations, crop livestock systems based on legumes, etc.
- Pest regulation assured through enhanced activity of biological control agents achieved by introducing and/or conserving natural enemies and antagonists
Excerpt 2: Prevention (Cultural Methods)
adapted from UC IPM
The most effective, long-term way to manage pests is by using a combination of methods that work better together than separately. Approaches for managing pests are often grouped in the following categories.
- Biological control is the use of natural enemies—predators, parasites, pathogens, and competitors—to control pests and their damage. Invertebrates, plant pathogens, nematodes, weeds, and vertebrates have many natural enemies.
- By protecting or building habitat for natural enemies, you will attract and support natural enemy populations- explore the following brochure to learn more: Farming for Pest Prevention
- Cultural controls are practices that reduce pest establishment, reproduction, dispersal, and survival. For example, changing irrigation practices can reduce pest problems, since too much water can increase root disease and weeds.
Mechanical and physical controls
- Mechanical and physical controls kill a pest directly or make the environment unsuitable for it. Traps for rodents are examples of mechanical control. Physical controls include mulches for weed management, steam sterilization of the soil for disease management, or barriers such as screens to keep birds or insects out.
For example of the physical controls mentioned in the excerpt above, row cloth, as we learned about in the last lesson, both prevents evapotranspiration and can provide a physical barrier to protect crops from insect pests. Pictured below: Intercropping (L) and row cloth creating a physical barrier (R).
“Crop rotation is one of the oldest and most effective cultural control strategies. Growing a single crop year after year in the same field gives pest populations sufficient time to become established and build up to damaging levels. Rotating the field to a different type of crop can break this cycle by starving pests that cannot adapt to a different host plant. Farmers in the Midwest, for example, can reduce populations of wireworms (Elateridae) and rootworms (Diabrotica spp.) in corn fields by switching to oats, wheat, or legumes. Similarly, the clover root curculio (Sitona hispidula) that feeds exclusively on legumes can be eliminated by switching from clover or alfalfa to corn or small grains. Rotation schemes have also proven successful for controlling pests in pasture lands. Crop rotation schemes work because they increase the diversity of a pest’s environment and create discontinuity in its food supply. In diversified vegetable production, crop plans for effective crop rotation are important to reduce pest populations. Each crop family has different pests and soil diseases it’s susceptible to. If you continue to plant the same crop family in the same location, you provide food for the pests and they thrive. Different crop families have different “return times” – the time that a farm should wait before growing that crop familiy to the same growing area.” ( from Meyer, NC State University, Source here)
It’s important to note that Agroecology is inherently organic and not compatible with applying any chemical pesticides or fertilizers. Pest control in agroecology relies mainly in the effective design of the agroecosystem that includes principles and practices to enhance the natural control of pest, weeds and diseases. However, in the case of emergency, some agroecological farmers apply “organic” pesticides until they find out and correct the cause of the pest outbreak. Pests can be a “messenger” by telling the farmer that a process or element at the farm is not working well. In this sense a pest can be seen as a symptom of a problem, rather than a problem itself. Here is a list of approved organic inputs that can be used in case of emergency, it is important to note that even if the organic pesticides come from natural sources, the majority of them are broad spectrum pesticides, meaning they decrease the populations of all insects and even other creatures, not only the “pests.” Because beneficial insects such as predatory insects and natural enemies are also affected, the farmer must be ready to implement practices that recover the populations of beneficial insects, for example plant more flowers with pollen to attract them or buy eggs of beneficial insects and provide them suitable conditions to re-establish.
Article 1: Farming for Pest Prevention
Rethinking Pests – Edible Insects
Going beyond just managing pests, what if we thought about insects in another way? For instance, did you know that a lot of the world’s cultures eat insects? Indeed, insects are a very good source of protein that can be produced in a sustainable way. They also can provide environmental services such as pests control and pollination. However, in 2001, total expenditures for pesticides in the U.S. were $11.09 billion, of which $7.4 billion was spent by the agricultural industry. This begs the question, if the United States deemed insects a food crop, how many pesticides might we use?
Edible Insects for sale
Excerpt 3: Edible insects contributing to food security?
by Arnold Van Huis | Agriculture and Food Security, 2015
Insects as Food
In tropical countries most insect species are collected from nature. An inventory of the edible insect species eaten from all over the world, incorporating only scientific names and not vernacular names, yielded more than 2000 species . Some countries stand out in the number of insect species eaten. This, however, is mostly related to the amount of research done. For example, Ramos-Elorduy wrote an impressive numbers of articles on entomophagy (the eating of insects) in Mexico (e.g. ), and Belgian scientists recorded more than 60 edible caterpillars from the Democratic Republic of Congo, a former Belgian colony . This also means that many edible insect species have not yet been identified, requiring further exploration .
The reason that insects are predominantly eaten in tropical countries is that they are larger and often occur clumped, which facilitates harvesting. Also, in the absence of a winter season, insect species can be found during the whole year. Most insect species occur seasonally as they depend on the availability of their host plant; others may occur throughout the year such as most aquatic insects. Representatives from almost all insect groups are eaten such as beetles (31 %), caterpillars (18 %), wasps, bees and ants (15 %), crickets, grasshoppers and locusts (13 %), true bugs (11 %), and termites, dragonflies, flies and others (12 %) . Other arthropod groups such as spiders and scorpions are also eaten. Some species are semi-domesticated which means that certain measures are taken to make the harvesting more predictable . For example, palm trees may be cut deliberately, in order to trigger palm weevils of the genus Rhynchophorus (Coleoptera: Curculionidae) to oviposit on the trunk. After a certain time the larvae are then harvested. These larvae are considered an absolute delicacy in many parts of the world. In Central Africa the collection of arboreal, foliage consuming caterpillars is facilitated by manipulating host tree distribution and abundance, shifting cultivation, fire regimes, host tree preservation, and manually introducing caterpillars to a designated area.
There is little information about how often and how much insects are consumed in the tropics (see for some examples chapter 2 of Van Huis et al. ). This is mainly because national agricultural statistics do not include insects as food or feed. The large majority of insects in developing countries are gathered from wild populations in nature, in farmlands or in forests. Those are self-consumed and the access sold for cash at village markets or to middlemen and wholesalers at the farm gate. Edible insects offer a cheap and efficient opportunity to improve livelihoods and the quality of traditional diets among vulnerable people.
Recently in western countries the interest of using insects as food has gained momentum. A number of companies have started to produce insects for human consumption. For example in the United States, these are often crickets which are marketed in processed products such as protein bars. In some countries they are already sold in supermarkets.