What are insects and why do we need them?
Insects have six legs, three body segments (head, thorax, abdomen), two antennae, and generally one or two pairs of wings. They comprise over 80% of terrestrial species on Earth, and include bees, ants, butterflies, grasshoppers, and beetles, among many others. Insects drive the production of essential seeds, fruits, and vegetables via pollination, and are necessary decomposers of organic matter. Further, insects are keystone species that provide invaluable ecosystem services that extend beyond pollination, by providing biological control of pests, and acting as bio-indicators of healthy streams and soils. Insects form the base of complex ecological food webs in agricultural, natural, and urban areas, shaping the appearance, beauty and complexity of these diverse landscapes.
At the same time, many insects are significant pests of agricultural crops and urban areas. They spread diseases that can endanger human, plant, and animal health. Invasive insect species can destroy crops and upset the balance of healthy ecosystems, which threatens global biodiversity, food security, and human livelihoods. Additionally, insect-borne diseases cause millions of human deaths each year.
Increasing globalization and changing climates are constantly reshaping the abundance, diversity, and distribution of insect communities. It is imperative that we understand the forces underlying where and how insects live, so we can maintain healthy and productive ecosystems that support beneficial insects and eradicate or minimize the impact of pest insects.
The evidence for global insect declines is irrefutable.
Populations of many insect species have been declining worldwide, and entomologists and environmentalists have been acknowledging this phenomenon since the late 1930s.[1, 2] In 2017, a long-term study found declines of more than 75% of insects in protected areas in Germany,[3] sparking an international debate about global insect declines and how widespread they really are[4, 5]. Despite the criticism of specific studies,[5] the overall trend is clear: these declines are occurring not only in developing areas of the world,[6, 7] but also remote places that are not directly touched by human disturbance like the Arctic,[8] providing more than enough evidence to incite alarm and inspire action to halt and reverse these declines.[9]
Multiple factors are driving insect declines.
The factors causing insect declines are similar to those causing overall biodiversity declines.[10] These include loss and fragmentation of habitat;[11] pollution from light, microplastics, and synthetic pesticides;[12, 13, 14] spread of pathogens and parasites;[15] and climate change.[16, 17] In many cases, these stressors are likely working together to drive declines of the world’s insect biodiversity.[10]
A world without insects.
The breadth of ecosystem services provided by insects corresponds with an estimated annual economic value of US$57 billion.[18] Insect pollinators (e.g. bees, flower-flies, and butterflies) pollinate over 85% of wild flowering plants[19] and over 75% of agricultural crop species.[20] The loss of partial or whole insect communities can have disastrous effects for food webs[21, 22] and reduce an area’s ability to recover after disturbances.[23] Many dragonfly species can be biological controls for disease-carrying mosquitoes,[24] and lacewings can control agricultural pests like aphids and mites.[25] Finally, beetles can be highly important for the removal of waste products from the environment,[26] and the introduction of dung beetles onto farms has been shown to promote disease resistance against foodborne pathogens.[27]
References
[1] Patch, E.M. (1938). Without Benefit of Insects Bulletin of the Brooklyn Entomological Society 33(1): 1-9
[2] Carson, R. (1962). Silent Spring. Boston: Houghton Mifflin Company. Cambridge, MA.
[3] Hallmann, C.A., Sorg M., Jongejans E., Siepel H., Hofland N., et al. (2017). More than 75 percent decline over 27 years in total flying insect biomass in protected areas. PLOS ONE 12(10): e0185809
[4] Montgomery, G.A., Dunn R.R., Fox R., Jongejans E., Leather S.R., et al. (2020). Is the insect apocalypse upon us? How to find out. Biological Conservation 241: e108327.
[5] Thomas, C.D., Jones T.H., & Hartley S.E. (2019). “Insectageddon”: A call for more robust data and rigorous analyses. Global Change Biology 25:1891-1892.
[6] Wepprich, T., Adrion J.R., Ries L., Wiedmann J., & Haddad N.M. (2019). Butterfly abundance declines over 20 years of systematic monitoring in Ohio, USA. PLOS ONE 14(7): e0216270.
[7] Macgregor, C.J., Williams J.H., Bell J.R., and Thomas C.D. (2019). Moth biomass increases and decreases over 50 years in Britain. Nature Ecology & Evolution 3: 1645-1649.
[8] Loboda, S., Savage, J., Buddle, C.M., Schmidt, N.M., and Høye, T.T. (2018). Declining diversity and abundance of High Arctic fly assemblages over two decades of rapid climate warming. Ecography, 41: 265-277.
[9] Forister, M.L., Pelton E.M., and Black S.H. (2019). Declines in insect abundance and diversity: We know enough to act now. Conservation Science and Practice 1:e80.
[10] Sanchez-Bayo, F., and Wyckhuys K.A.G. (2019). Worldwide decline of the entomofauna: A review of its drivers. Biological Conservation 232: 8-27.
[11] Hedges, S.B., Cohen W.B., Timyan J., and Yang Z. (2018). Haiti’s biodiversity threatened by nearly complete loss of primary forest. Proceedings of the National Academy of Sciences 115(46): 11850-11855.
[12] Owens, A. C., Cochard, P., Durrant, J., Farnworth, B., Perkin, E. K., & Seymoure, B. (2020). Light pollution is a driver of insect declines. Biological Conservation, 241, 108259.
[13] Oliveira, M., Ameixa, O. M., & Soares, A. M. (2019). Are ecosystem services provided by insects "bugged" by micro (nano) plastics? TrAC Trends in Analytical Chemistry.
[14] Douglas, M.R., Sponsler, D.B., Lonsdorf, E.V., & Grozinger, C. M. (2019). Rising insecticide potency outweighs falling application rate to make US farmland increasingly hazardous to insects. bioRxiv, 715763.
[15] Satterfield, D.A., Maerz, J.C., & Altizer, S. (2015) Loss of migratory behavior increases infection risk for a butterfly host. Proc. Biol. Sci. 282(1801): 20141734.
[16] Harris, J.E., Rodenhouse N.L., & Holmes R.T. (2019). Decline in beetle abundance and diversity in an intact temperate forest linked to climate warming. Biological Conservation 240: e108219.
[17] Soroye, P., Newbold T., & Kerr J. (2020). Climate change contributed to widespread declines among bumble bees across continents. Science 367(6478): 685-688.
[18] Losey, J. E., & Vaughan, M. (2006). The economic value of ecological services provided by insects. Bioscience, 56(4), 311-323.
[19] Ollerton, J., Winfree, R., & Tarrant, S. (2011). How many flowering plants are pollinated by animals? Oikos, 120(3), 321-326.
[20] Klein, A. M., Vaissiere, B. E., Cane, J. H., Steffan-Dewenter, I., Cunningham, S. A., Kremen, C., & Tscharntke, T. (2007). Importance of pollinators in changing landscapes for world crops. Proceedings of the Royal Society B: Biological sciences, 274(1608), 303-313.
[21] Lister, B.C., & Garcia, A. (2018). Climate-driven declines in arthropod abundance restructure a rainforest food web. Proceedings of the National Academy of Sciences, 115(44), E10397-E10406.
[22] Thomas, J.A., Telfer, M.G., Roy, D.B., Preston, C.D., Greenwood, J.J.D., Asher, J., ... & Lawton, J.H. (2004). Comparative losses of British butterflies, birds, and plants and the global extinction crisis. Science, 303(5665), 1879-1881.
[23] Isbell, F., Tilman, D., Reich, P. B., & Clark, A. T. (2019). Deficits of biodiversity and productivity linger a century after agricultural abandonment. Nature Ecology & Evolution, 3(11), 1533-1538.
[24] Ong’wen, F., Onyango, P.O. & Bukhari, T. (2020). Direct and indirect effects of predation and parasitism on the Anopheles gambiae mosquito. Parasites & Vectors 13, 43.
[25] Senior, L. J., McEwen, P. K., McEwen, P., New, T., & Whittington, A. (2001). The use of lacewings in biological control. Lacewings in the Crop Environment, 296-302.
[26] Nichols, E., Spector, S., Louzada, J., Larsen, T., Amezquita, S., Favila, M. E., & Network, T. S. R. (2008). Ecological functions and ecosystem services provided by Scarabaeinae dung beetles. Biological Conservation, 141(6), 1461-1474.
[27] Jones, M. S., Fu, Z., Reganold, J. P., Karp, D. S., Besser, T. E., Tylianakis, J. M., & Snyder, W. E. (2019). Organic farming promotes biotic resistance to foodborne human pathogens. Journal of Applied Ecology 56(5), 1117-1127.