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.
Insecticide use in the US.
Several recent reports suggest that insecticide use has decreased in recent decades. Those of us who live in the Great Plains know better 1.
For example, neonicotinoid insecticidal seed treatments currently coat the seeds of nearly all planted corn, soybean, sunflower, canola, alfalfa, wheat, and cotton (to name a few) 4. These crops occupy 13% of the terrestrial land surface of the contiguous United States 6. The dosage of this insecticide is slight (approximately 37.5 g a.i. per acre in corn). But the toxicity of imidacloprid and clothianidin is 7,300–10,800 times more toxic to honey bees than DDT 7. And only 2–20% of the seed coating is taken up by the plant 9. The resting place of the other 80–98% of the chemical is largely unknown, although neonicotinoids are turning up in untreated plants 11,12 and in water systems 14,15. This doesn’t count how much insecticide is sprayed on to crops.
Pesticides can be an important tool, but farmers need to realize that there are consequences of applying pesticides.
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
1 Fausti, S. W. et al. Insecticide use and crop selection in regions with high GM adoption rates. Renewable Agriculture and Food Systems 27, 295–304 (2012).
2 Pedigo, L. P. Entomology and Pest Management. 816 (Prentice Hall, 2010).
3 Corn, L. C., Buck, E., H., Rawson, J. & Fischer, E. Harmful non-native species: issues for congress. Congressional Research Service Issue Brief, RL30123 (1999).
4 Douglas, M. R. & Tooker, J. F. Large-scale deployment of seed treatments has driven rapid increase in use of neonicotinoid insecticides and preemptive pest management in U. S. field crops. Environmental Science & Technology 49, 5088–5097 (2015).
5 Lockwood, J. A. Six-legged Soldiers., (Oxford University Press, 2010).
6 NASS. National Agricultural Statistics Service; http://www.nass.usda.gov/index.asp (USDA, 2015).
7 Pisa, L. W. et al. Effects of neonicotinoids and fipronil on non-target invertebrates. Environmental Science and Pollution Research 22, 68–102 (2015).
8 Basset, Y. et al. Arthropod diversity in a tropical forest. Science 338, 1481 (2012).
9 Sur, R. & Stork, A. Uptake, translocation and metabolism of imidacloprid in plants. Bulletin of Insectology 56, 35–40 (2003).
10 Lundgren, J. G., McDonald, T. M., Rand, T. A. & Fausti, S. W. Spatial and numerical relationships of arthropod communities associated with key pests of maize. Journal of Applied Entomology 136, 446–456 (2015).
11 Pecenka, J. R. & Lundgren, J. G. Non-target effects of clothianidin on monarch butterflies. . Science of Nature 102, 19 (2015).
12 Krupke, C. H., Hunt, G. J., Eitzer, B. D., Andino, G. & Given, K. Multiple routes of pesticide exposure for honey bees living near agricultural fields. PLoS ONE 7, e29268 (2012).
13 Bredeson, M. M. & Lundgren, J. G. Foliar and soil arthropod communities of sunflower (Helianthus annuus) fields of central and eastern South Dakota. . Journal of the Kansas Entomological Society in press (2015).
14 Hladik, M. L., Kolpin, D. W. & Kuivila, K. M. Widespread occurrence of neonicotinoid insecticides in streams in a high corn and soybean producing region, USA. Environmental Pollution 193, 189–196 (2014).
15 Main, A. R. et al. Widespread use and frequent detection of neonicotinoid insecticides in wetlands of Canada’s prairie pothole region. PLoS ONE 9, e92821 (2014).
16 Doxon, E. D. & Carroll, J. P. Feeding ecology of ring-necked pheasant and northern bobwhite chicks in conservation reserve program fields. Journal of Wildlife Management 74, 249–256 (2010).
17 Roseman, E. F., Schaeffer, J. S., Bright, E. & Fielder, D. G. Angler-caught piscivore diets reflect fish community changes in Lake Huron. Transactions of the American Fisheries Society 143, 1419–1433 (2014).
18 Klein, A.-M. et al. Importance of pollinators in changing landscapes for world crops. Proceedings of the Royal Society B 274, 303–313 (2007).
19 Steinhauer, N. A. et al. A national survey of manged honey bee 2012–2013 annual colony losses in the USA: results from the Bee Informed Partnership. Journal of Apicultural Research 53, 1–18 (2014).
20 van Huis, A., van Gurp, H. & Dicke, M. The Insect Cookbook: Food for a Sustainble Planet., (Columbia University Press, 2014).
21 Lehman, R. M. et al. Understanding and enhancing soil biological health: The solution for reversing soil degradation. Sustainability 7, 988–1027 (2015).
22 Bluoin, M. et al. A review of earthworm impact on soil function and ecosystem services. European Journal of Soil Science 64, 161–182 (2013).
23 Bottinelli, N. et al. Why is the influence of soil macrofauna on soil structure only considered by soil ecologists? Soil & Tillage Research 146, 118–124 (2015).
24 Lundgren, J. G. Relationships of Natural Enemies and Non-prey Foods., (Springer International, 2009).
25 Liebman, M. in Ecological Management of Agricultural Weeds. (eds M. Liebman, C. L. Mohler, & C. P. Staver) 375–408 (Cambridge University Press, 2001).
26 McFadyen, R. E. C. Biological control of weeds. Annual Review of Entomology 43, 369–393 (1998).
27 Symondson, W. O. C., Sunderland, K. D. & Greenstone, M. H. Can generalist predators be effective biological control agents? Annual Review of Entomology 47, 561–594 (2002).
28 Landis, D. A., Gardiner, M. M., van der Werf, W. & Swinton, S. M. Increasing corn for biofuel production reduces biocontrol services in agricultural landscapes. Proceedings of the National Academy of Sciences 105, 20552–20557 (2008).
29 Lundgren, J. G. & Wiedenmann, R. N. Tritrophic interactions among Bt (Cry3Bb1) corn, aphid prey, and the predator Coleomegilla maculata (Coleoptera: Coccinellidae). Environmental Entomology 34, 1621–1625 (2005).
30 Lundgren, J. G., Prischmann, D. A. & Ellsbury, M. M. Analysis of the predator community of a subterranean herbivorous insect based on polymerase chain reaction. Ecological Applications 19, 2157–2166 (2009).
31 Lundgren, J. G. & Fergen, J. K. Enhancing predation of a subterranean insect pest: A conservation benefit of winter vegetation in agroecosystems. Applied Soil Ecology 51, 9–16 (2011).
32 Losey, J. E. & Vaughan, M. The economic value of ecological services provided by insects. BioScience 56, 311–323 (2006).
33 Lundgren, J. G. & Fausti, S. W. Trading biodiversity for pest problems. Science Advances 1 (2015).
34 Schmid, R. B., Lehman, R. M., Brözel, V. S. & Lundgren, J. G. Gut bacterial symbiont diversity within beneficial insects linked to reductions in local biodiversity. Annals of the Entomological Society of America in press (2015).
35 Root, R. B. Organization of a plant-arthropod assocation in simple and diverse habitats: The fauna of collards (Brassica oleraceae). Ecological Monographs 43, 95–124 (1973).
36 Andow, D. A. Vegetational diversity and arthropod population response. Annual Review of Entomology 36, 561–586 (1991).
37 Letourneau, D. K. et al. Does plant diversity benefit agroecosystems? A synthetic review. Ecological Applications 21, 9–21 (2011).
38 Denno, R. F., McClure, M. S. & Ott, J. R. Interspecific interactions in phytophagous insects: competition reexaminated and resurrected. Annual Review of Entomology 40, 297–331 (1995).
39 Finke, D. L. & Snyder, W. E. Conserving the benefits of predator biodiversity. 143 (2010).
40 Letourneau, D. K., Jedlicka, J. A., Bothwell, S. G. & Moreno, C. R. Effects of Natural Enemy Biodiversity on the Suppression of Arthropod Herbivores in Terrestrial Ecosystems. Annual Review of Ecology, Evolution, and Systematics 40, 573–592 (2009).
41 Lundgren, J. G., Haye, T., Toepfer, S. & Kuhlmann, U. A multi-faceted hemolymph defense against predation in Diabrotica virgifera virgifera larvae. Biocontrol Science and Technology 19, 871–880 (2009).
42 Lundgren, J. G., Toepfer, S., Haye, T. & Kuhlmann, U. Hemolymph defence in an invasive herbivore: its breadth of effectiveness against predators. Journal of Applied Entomology 134, 439–448 (2010).
43 Welch, K. D. & Lundgren, J. G. Predator responses to novel haemolymph defences of western corn rootworm (Diabrotica virgifera) larvae. Entomologia Experimentalis et Applicata 153, 76–83 (2014).
44 Lundgren, J. G. & Fergen, J. K. Predator community structure and trophic linkage strength to a focal prey: the influence of the prey’s anti-predator defense. Molecular Ecology 23, 3790–3798 (2014).
45 Wardle, D. A. Impacts of disturbance on detritus food webs in agro-ecosystems of contrasting tillage and weed management practices. . Advances in Ecological REsearch 26, 105–185 (1995).
46 Kladivko, E. J. Tillage systems and soil ecology. Soil & Tillage Research 61, 61–76 (2001).
47 Landis, D. A., Wratten, S. D. & Gurr, G. M. Habitat management to conserve natural enemies of arthropod pests in agriculture. Annual Review of Entomology 45, 175–201 (2000).
48 Stern, V. M., Smith, R. F., van den Bosch, R. & Hagen, K. S. The integrated control concept. Hilgardia 29, 81–101 (1959).
49 Van den Bosch, R. The Pesticide Conspiracy. (University of California Press, 1989).
50 Pimentel, D. Environmental and economic costs of the application of pesticides primarily in the United States. Environment, Development, and Sustainability 7, 229–252 (2005).
51 Bianchi, F. J. J. A., Booij, C. J. H. & Tscharntke, T. Sustainable pest regulation in agricultural landscapes: a review on landscape composition, biodiversity and natural pest control. Proceedings of the Royal Society B 273, 1715–1727 (2006).
52 Begum, M., Gurr, G. M., Wratten, S. D. & Nicol, H. I. Flower color affects tri-trophic-level biocontrol interactions. Biological Control 30, 584–590 (2004).
53 Clark, A. Managing Cover Crops Profitably, 3rd Edition. (USDA, 2007).
54 Lundgren, J. G. & Fergen, J. K. The effects of a winter cover crop on Diabrotica virgifera (Coleoptera: Chrysomelidae) populations and beneficial arthropod communities in no-till maize. Environmental Entomology 39, 1816–1828 (2010).
55 Tooker, J. F. & Frank, S. D. Genotypically diverse cultivar mixtures for insect pest management and increased crop yields. Journal of Applied Ecology 49, 974–985 (2012).
56 Parajulee, M. N., Montandon, R. & Slosser, J. E. Relay intercropping to enhance abundance of insect predators of cotton aphid (Aphis gossypii Glover) in Texas cotton. International Journal for Pest Management 43, 227–232 (1997).
57 Khan, Z. R. et al. Intercropping increases parasitism of pests. Nature 388, 631–632 (1997).
58 Prasifka, J. R. et al. Effects of living mulches on predator abundance and sentinel prey in a corn–soybean–forage rotation. Environmental Entomology 35, 1423–1431 (2006).
59 Bullock, D. G. Crop rotation. Critical Reviews in Plant Sciences 11, 309–326 (1992).
60 Collins, K. L., Boatman, N. D., Wilcox, A., Holland, J. M. & Chaney, K. Influence of beetle banks on cereal aphid predation in winter wheat. Agriculture, Ecosystems and Environment 93, 337–350 (2002).
61 Haaland, C., Naisbit, R. E. & Bersier, L.-F. Sown wildflower strips for insect conservation: a review. Insect Conservation and Diversity 4, 60–80 (2011).
62 Choate, B. A. & Lundgren, J. G. Protein-marking-based assessment of infield predator dispersal. Biocontrol Science and Technology 24, 1183–1187 (2014).
63 Tscharntke, T. et al. Conservation biological control and enemy diversity on a landscape scale. Biological Control 43, 294–309 (2007).
64 Gardiner, M. M. et al. Landscape diversity enhances biological control of an introduced crop pest in the north-central USA. Ecological Applications 19, 143–154 (2009).
65 Montgomery, D. R. Dirt: The Erosion of Civilizations. (University of California Press, 2007).
66 FAO. The State of Food and Agriculture: Paying Farmers for Environmental Services., Vol. 38 (Food and Agriculture Organization of the United Nations, 2007).