Insects as the Solution Instead of the Problem.
Jonathan Lundgren, PhD
Blue Dasher Farm, Brookings, South Dakota
Many people’s innate opinion is that the only good bug is a dead bug. When an insect is out of place, we stomp, spray, scratch, swat, flick, plow, cut, and smash to regain control of the situation. After all, entomologists count thousands of species of insects that can be regarded as pests. Although inherently impossible to know for sure, two numbers I have seen kicked around by experts note 3,500-15,000 insect species worldwide that may be considered pests by humans (2,3). These insects eat our food, destroy our homes and yards, bite our children in the night, get into our cupboards, transmit diseases, etc. Indeed, insects have killed more soldiers than any bullets or bombs; they have literally turned the tides of war (5).
Thousands of species of pest insects! We need to kill all of these insects before it is too late, right?
Wrong. Potentially dead wrong.
What’s wrong with killing pests? When we take a pest-centric view of insects, it is easy to forget that for every pest species, there are between 400-1700 species of insects that are actually helping the human race (8). For example, 93% of species in a corn field are beneficial or neutral to corn production (80% of these species are predators) (10). In one-fifth of the area of a normal South Dakota sunflower field, non-pest arthropods in the soil outnumber the human population on the planet (there are 27.5 million arthropods per acre) (12,13). Without this majority of beneficial and neutral species, food webs and natural ecosystem functioning come to a screeching halt. Pests are important, and should not be ignored. But perhaps we should better understand what pests are telling us before we toss the baby out with the bathwater.
Insects as friendlies. Like it or not, the human race depends on insects. If you like to hunt, fish, or bird watch, thank an insect (16,17). Insects are the nutritional basis for many of the species that we enjoy for recreation. If you like fruits, vegetables, and flowers, then thank an insect. One third of our diets are directly dependent on pollinators like bees, beetles, and butterflies (18). And these pollinators are in steep decline. Imagine losing 45% of your crop every year- this is what bee keepers are experiencing right now (19).
North America and Europe are the only two cultures that do not rely on insects as a major source of protein in their diets (20). Insects are more efficient at converting feed into protein than any of the livestock we currently produce (20); if you enjoy crab legs or lobsters…guess what? These are large “bugs”.
Much of the current dialogue on soil health revolves around the importance soil biology (21). This term is often synonymized with soil microbiology, but soil invertebrates are a crucial aspect in soil health (22,23). For example, insects and earthworms contribute to soil structure and genesis, improve water infiltration, and are a critical component of soil nutrient cycles. Also, estimates by my team suggest that there are as many as 1 billion soil invertebrates per acre; at this number, soil insects, mites and their kin represent a significant source of carbon in their own right!
Insects are nature’s pesticides. Granivores, seed feeding insects, eat the seeds of weeds (sometimes as many as 10% of weed seeds per day) (24). Defoliating insects can act as stressors on weeds (25,26). Predators and parasitoids act as nature’s insecticides, inflicting high tolls against pests (27,28). A single lady beetle larva can eat 300 aphids during its 10 day development, and even more per day as an adult (29). We have identified dozens of predators of corn rootworm larvae in corn fields by looking for fragments of rootworm DNA in the stomachs of predatory insects in the soil (30,31). These insects are a free source of pest management, and we can use them to make farming more profitable and environmentally sustainable.
All told, insects contribute $70 billion to our economy every year, and this is likely an underestimate (28,32).
The elephant in the room. If insecticides were the answer to pest problems, then why didn’t we eradicate pests 60 years ago? Insect pests are not the problem. Insect pests are a symptom of the problem. When faced with a pest problem, many entomologists and crop consultants quickly advise a spray recommendation based on economic injury levels of the pest. In contrast, when I see a farm field with a perpetual insect pest problem, the first question that I ask is “what is out of whack in this field to produce such an outbreak?” If all we are doing is solving symptoms with a quick pesticide application, and ignoring the problem, then we will continuously battle pest outbreaks.
If pests are the symptom, then what is the problem? Two lines of evidence suggest that our highly disturbed agroecosystems have a lack of diversity, and when we return biodiversity to our cropland, farmers find that insect pest outbreaks are attenuated or eliminated altogether.
Innovative farmers are leading the scientists in developing food production systems that regenerate the soil. These processes are based on encouraging biodiversity and reducing disturbances to their cropland (especially tillage). The first line of evidence that diversity is a key driver of pest outbreaks is that farmers that are regenerating soil health through biodiversity are abandoning their insecticide inputs. They no longer need them.
Science is reinforcing these observations with empirical data. Increasing diversity in simplified systems is associated with fewer pests, and we recently documented that the balance of species networks were predictive of pest abundance in corn fields on actual farms (33). Specifically, more diversity and a greater balance of species’ abundances within a community of insects leads to fewer pests. The number of species (insects and plants) that live in a corn field is approximately 25% of the number that lived in a native prairie (at least in eastern South Dakota; (34). This means that we have a lot of work to do to increase species diversity in corn fields to even come close to approaching the healthy insect communities that once inhabited these same fields.
How does diversity stop pest problems? The humbling answer is that we may never fully understand the myriad and complex ways in which diverse communities and their interactions contribute to pest reductions. But we do know a couple of the ways that biodiversity functions (35).
First, as diversity increases within a habitat, especially as more plant species are included, it often reduces herbivore pressure from pests (36,37). This could be because the crop plant is more difficult to find for the pest, or it could be because the crop plant is changed in structure or physiology in ways that make it less suitable for the pest. Additionally, as more insect species occur within a habitat, they often compete for existing niches or alter host plants (38); in this way competition with other herbivores could help to reduce the dominance of a pest species.
Another way that diversity works is that predation on pests is enhanced when species diversity within a community is increased (39,40). Our data suggests that pests are often defended in some way. This defense may come from being well hidden, or having sharp spines or stings, or being poisonous to predators. For example, corn rootworm larvae have distasteful, sticky blood that repels many predators (41-43). And predators only eat these rootworms if the predator community in a cornfield is saturated (the rootworm larvae are the last thing left on the shelf, so to speak) (44).
How do we increase species diversity and still produce food? What can we do to promote beneficial species and minimize pests? The answer is conceptually very simple: Reduce disturbance. Increase diversity. Practically instituting these simple concepts can be more daunting, but there are numerous agronomically proven ways that can function within traditional cropping operations.
Reducing disturbance. Tillage typically kills soil biology- indeed, that is one of its primary goals (45). And while removing the soil dwelling life stages of a pest may seem like a sensible practice in the short term, it can take a long time for that soil community to heal (46). Heavily disturbed systems are difficult for natural enemies to persist in, and so biotic resistance to pest proliferation is minimized when a monoculture of a crop is subsequently planted into a black field (47). So to resist these pest populations whose enemies have now been killed, we add additional inputs (insecticides, for example) to maintain the productivity of the disturbed system.
Unnecessary pesticide use is a form of disturbance, and is a bad business decision. Prophylactic insecticide use (using insecticidal seed treatments, Bt crops, systemic insecticides in cattle, etc.) is expensive and should be strongly questioned. For years, this form of “insurance pest management” (spraying regardless of whether a pest problem is present) was the norm (48). The outcomes of this unnecessary pesticide use were lower farm profitability, increased pest resistance, non-target effects of the pesticides on beneficial species and wildlife, and human health problems (49,50). Those who do not learn from the past are doomed to repeat it. It is often foolish to take advice on whether to spray an insecticide from someone who is selling you the product. Let’s be smarter than that, folks.
Increase diversity. On par with tillage in its negative effects, bare soil should be avoided in cropland. Vegetation cover or plant residue fosters insect diversity and pest suppression by providing a greater number of tiny habitats where insects can make a living, and greater prey diversity for predators (40,47,51,52). Although there are patterns starting to emerge from the scientific research that support the use of diversity, many studies remain to be done from an applied point of view. For example, science needs to evaluate whether diversified food production systems improve farm profitability, rather than simply asking if insect diversity or pest density are affected by a specific practice. In this way, again, innovative farmers are leading the charge by implementing practices that increase diversity in their systems, and scientists can learn by observing these farms.
Covering the soil in cropland can be accomplished in many ways. Cover crops make a lot of ecological and agronomic sense (53). We found that simply including a grass cover crop before corn can increase predators and reduce corn rootworms and the damage that this pest inflicts (54). Now we are assessing whether these cover crops can be economically competitive (or superior) to “traits-based management” (Bt corn, insecticidal seed treatments, etc.) on actual farms throughout the Great Plains. Diversity in cover crop mixes anecdotally seems to be equally important for conserving friendly insects in your farm field. Given that the science is trailing the farmers, I have to rely on observations from operating farms. Regarding cover crop diversity, my experience leads me to advocate “some is better than none, and more is better than less”. And we are now designing the studies to test these observations.
Other ways to increase vegetation diversity include increasing the number of crop varieties within a field (55), intercropping different crops in the same field or undersowing non-crop plants beneath a cash crop’s canopy (56-58), and lengthening crop rotations (59). Some practices work better in certain systems than others, and a lot more research needs to be done that investigates the effects of these different practices on insect communities, and how to use these practice optimally. Often times the synergies and symbioses that drive these interactions remain poorly understood.
Insects move, sometimes over long distances. And decisions elsewhere on one’s farm can have implications for the insect community that resides within a particular field. In close range, field margins can and should be strategized to provide habitat for insect diversity. Practices like conservation strips and setting aside marginal lands with multispecies mixes can attract pollinators and predators that spill over into adjacent farmland (60,61). Although we know that predators can move in-field up to 300 ft per day (62), research that supports strategizing how to implement conservation strips most effectively is still in its infancy.
Farmers can have a fast and dramatic effect on increasing diversity, and the benefits of these practices accrue in space and time. Regional efforts to change crop and rangelands have important implications for local pest populations and biodiversity (63,64); but this requires coordination among land owners that presents challenges. Also, it took decades to degrade soils to their current state, and it will take years to fully restore the range of ecological functions that soil can provide (65). But what an exciting opportunity to document these changes as they happen in your operation.
Up to 40% of the terrestrial land surface of our planet is devoted to agroecosystems (66). Inherently, food production is an invasive, destructive process that lends itself to disturbance. We are never going to productively farm the prairie or the forest. This notwithstanding, pest outbreaks are telling us that we have do a hell of a lot better than we are right now. The question is not whether we can feed the world and conserve biodiversity. The question is what will happen if we don’t.
We can conserve biodiversity and produce food.
Jonathan Lundgren, PhD is an award-winning
research ecologist/entomologist studying the
development of sustainable food production
systems and environmental safety assessment
of pest and farm management practices for
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