View source for Biology:Decline in insect populations

{{Short description|Ecological trend recorded since the late 20th century}}
[[File:Journal.pone.0185809.g004.PNG|thumb|An annual decline of 5.2% in flying insect biomass found in nature reserves in Germany – about 75% loss in 26 years.<ref name=Hallmann2017PLoS/>]]

[[Biology:Insect|Insect]]s are the most numerous and widespread [[Biology:Class|class]] in the animal [[Biology:Kingdom|kingdom]], accounting for up to 90% of all animal species.<ref name="number">{{cite book |author=Erwin, Terry L. |url=http://entomology.si.edu/StaffPages/Erwin/T's%20updated%20pub%20PDFs%2010Jan2014/121_1995_Biodiversity-at-its-utmost.pdf |title=Biodiversity at its utmost: Tropical Forest Beetles |year=1997 |pages=27–40 |access-date=16 December 2017 |archive-url=https://web.archive.org/web/20181109151957/https://entomology.si.edu/staffpages/Erwin/T's%20updated%20pub%20PDFs%2010Jan2014/121_1995_Biodiversity-at-its-utmost.pdf |archive-date=9 November 2018 |url-status=live}} In: {{cite book |url=https://archive.org/details/biodiversityiiun00reak |title=Biodiversity II |publisher=Joseph Henry Press, Washington, D.C. |year=1997 |isbn=9780309052276 |editor1=Reaka-Kudla, M.L. |editor2=Wilson, D. E. |editor3=Wilson, E. O. |url-access=registration}}</ref><ref>{{cite journal |last=Erwin |first=Terry L. |year=1982 |title=Tropical forests: their richness in Coleoptera and other arthropod species |url=https://repository.si.edu/bitstream/handle/10088/4383/Classic_papers_in_Foundations.pdf?sequence=1&isAllowed=y |url-status=live |journal=The Coleopterists Bulletin |volume=36 |pages=74–75 |archive-url=https://web.archive.org/web/20150923014947/https://repository.si.edu/bitstream/handle/10088/4383/Classic_papers_in_Foundations.pdf?sequence=1&isAllowed=y |archive-date=23 September 2015 |access-date=16 September 2018}}</ref> In the 2010s, multiple reports about the widespread '''decline in insect populations''' across multiple [[Biology:Order|orders]] have emerged. The reported severity had shocked many observers, even though it was preceded by the earlier findings of [[Biology:Pollinator decline|pollinator decline]], as well as anecdotal evidence of greater apparent abundance of insects earlier in the 20th century, such as the windscreen phenomenon.<ref name="Leather2017" /><ref name="SchwägerlYale2016" />  Possible causes are similar to those causing other [[Biology:Biodiversity loss|biodiversity loss]], namely [[Earth:Habitat destruction|habitat destruction]], including intensive agriculture; the use of [[Biology:Pesticide|pesticide]]s (particularly [[Biology:Insecticide|insecticide]]s); urbanisation, and industrialisation; [[Earth:Introduced species|introduced species]]; and - to a lesser degree and only for some regions - [[Earth:Climate change|climate change]].<ref name="Sánchez-Bayo2019" /> 

Most commonly, the declines involve reductions in abundance, though in some cases entire species are going extinct. The declines are far from uniform. In some localities, there have been reports of increases in overall insect population, and some types of insects appear to be increasing in abundance across the world.<ref name="Vogel2017" /> Not all insect orders are affected in the same way; most affected are [[Biology:Bee|bee]]s, butterflies, [[Biology:Moth|moth]]s, [[Biology:Beetle|beetle]]s, dragonflies and damselflies. However, many of the remaining groups have simply received less research, and comparative figures from earlier decades are often not available.<ref name="Vogel2017" /> In the few major global studies, estimates of the total number of insect species at risk of extinction range between 10% and 40%,<ref name="IPBES" /><ref name="Sánchez-Bayo2019" /><ref name="vanKlink2020" /><ref name="Isbell2022" /> though all of these estimates have been fraught with controversy.<ref name=Komonen2019>{{cite journal |last1=Komonen |first1=Atte |last2=Halme |first2=Panu |last3=Kotiaho |first3=Janne S. |title=Alarmist by bad design: Strongly popularized unsubstantiated claims undermine credibility of conservation science |journal=Rethinking Ecology |volume=4 |date=19 March 2019 |pages=17–19 |doi=10.3897/rethinkingecology.4.34440|doi-access=free }}</ref><ref name="Thomas2019" /><ref name="Desquilbet2020" /><ref name="Jähnig2021" />

Studies concur that in areas where insects are declining, their abundance had been diminishing for decades. Yet, those trends had not been spotted earlier, as there has historically been much less interest in studying insects in comparison to [[Biology:Mammal|mammal]]s, [[Biology:Bird|bird]]s and other [[Biology:Vertebrate|vertebrate]]s. One reason is the comparative lack of charismatic species of insects. In 2016, it was observed that while 30,000 insect species are known to inhabit [[Place:Central Europe|Central Europe]], there are practically no specialists in the region devoted to full-time monitoring.<ref name="Leather2017" /> This issue of insufficient research is even more acute in the developing countries. As of 2021, nearly all of the studies on regional insect population trends come from [[Earth:Europe|Europe]] and the {{wipe|United States}}, even though they account for less than 20% of insect species worldwide. With few exceptions, [[Earth:Africa|Africa]], [[Earth:Asia|Asia]] and [[Earth:South America|South America]] still lack multi-decade observations of insects which are required to draw conclusions about population trends on a large scale, and overcoming this obstacle is considered a top priority by expert entomologists.<ref name="Wagner2021">{{cite journal | publisher=National Academy of Sciences | last1=Wagner | first1=David L. | last2=Grames | first2=Eliza M. | last3=Forister | first3=Matthew L. | last4=Berenbaum | first4=May R. | last5=Stopak | first5=David | title=Insect decline in the Anthropocene: Death by a thousand cuts | journal=Proceedings of the National Academy of Sciences | volume=118 | issue=2 | date=2021-01-12 | pages=e2023989118 | issn=0027-8424 | pmid=33431573 | doi=10.1073/pnas.2023989118| pmc=7812858 | bibcode=2021PNAS..11823989W | doi-access=free }}</ref>

In response to the reported declines, increased insect related conservation measures have been launched. In 2018 the German government initiated an "Action Programme for Insect Protection"<ref name=FAO2019/><ref name=BMU/> Their goals include promoting insect habitats in the agricultural landscape, and reducing pesticide use, [[Astronomy:Light pollution|light pollution]], and pollutants in soil and water.<ref name="BMU" /> In 2019 a group of 27 British entomologists and ecologists wrote an open letter calling on the research establishment in the UK "to enable intensive investigation of the real threat of ecological disruption caused by insect declines without delay".<ref name=Leather2019/>

==Context==
[[File:Melanoplus spretusAnnReportAgExpStaUM1902B.jpg|thumb|A 1902 illustration of a Rocky Mountain locust. These insects were seen in swarms estimated at over 10 trillion members as late as 1875. Soon after, their population rapidly declined, with the last recorded sighting in 1902, and the species formally declared extinct in 2014.]]

The fossil record concerning insects stretches back hundreds of millions of years. It suggests there are ongoing background levels of both [[Biology:Speciation|new species appearing]] and extinctions. Very occasionally, the record also appears to show mass extinctions of insects, understood to be caused by natural phenomena such as volcanic activity or meteor impact. The [[Earth:Permian–Triassic extinction event|Permian–Triassic extinction event]] saw the greatest level of insect extinction, and the [[Earth:Cretaceous–Paleogene extinction event|Cretaceous–Paleogene]] the second highest. Insect diversity has recovered after mass extinctions, as a result of periods in which new species originate with increased frequency, although the recovery can take millions of years.<ref name=fossil/>

Concern about a human-caused [[Earth:Holocene extinction|Holocene extinction]] has been growing since the late 20th century, although much of the early concern was not focused on insects. In a report on the world's [[Biology:Invertebrate|invertebrate]]s, the [[Organization:Zoological Society of London|Zoological Society of London]] suggested in 2012 that insect populations were in decline globally, affecting [[Biology:Pollination|pollination]] and food supplies for other animals.<ref name=ZSL/><ref name=BorrellSA4Sept2012/><ref name="SchwägerlYale2016"/><ref name=NYTeditorial29Oct2017/> It estimated that about 20 percent of all invertebrate species were threatened with extinction, and that species with the least mobility and smallest ranges were most at risk.<ref name=ZSL/>

Studies finding insect decline have been available for decades—one study tracked a decline from 1840 to 2013—but it was the 2017 re-publication of the German nature reserves study<ref name=Hallmann2017PLoS/> that saw the issue receive widespread attention in the media.<ref name=Leather2017/><ref name="SchwägerlYale2016"/> The press reported the decline with alarming headlines, including "Insect [[Unsolved:Apocalypse|Apocalypse]]".<ref name=NYTeditorial29Oct2017/><ref name=JarvisNYT27Nov2018/> Ecologist Dave Goulson told ''The Guardian'' in 2017: "We appear to be making vast tracts of land inhospitable to most forms of life, and are currently on course for ecological [[Unsolved:Armageddon|Armageddon]]."<ref name=DCGuardian18Oct2017/> For many studies, factors such as [[Earth:Relative species abundance|abundance]], biomass, and [[Biology:Species richness|species richness]] are often found to be declining for some, but not all locations; some species are in decline while others are not.<ref name="Thomas2019"/> The insects studied have mostly been butterflies and moths, bees, beetles, dragonflies, damselflies and stoneflies. Every species is affected in different ways by changes in the environment, and it cannot be inferred that there is a consistent decrease across different insect groups. When conditions change, some species adapt easily to the change while others struggle to survive.<ref name=Reckhaus2017/>

A March 2019 statement by the Entomological Society of America said there was not yet sufficient data to predict an imminent mass extinction of insects and that some of the extrapolated predictions might "have been extended well past the limits of the data or have been otherwise over-hyped".<ref name=FAQEntSocAm2019/> For some insect groups such as some butterflies, moths, bees, and beetles, declines in abundance and diversity have been documented in European studies. These have generally led to an overall pattern of decline, but there are variable trends for individual species within groups. For instance, a minority of British moths are becoming more common.<ref>{{Cite journal|last1=Boyes|first1=Douglas H.|last2=Fox|first2=Richard|last3=Shortall|first3=Chris R.|last4=Whittaker|first4=Robert J.|date=2019|title=Bucking the trend: the diversity of Anthropocene 'winners' among British moths|url=https://escholarship.org/uc/item/6hz0x33v|journal=[[Earth:Frontiers of Biogeography|Frontiers of Biogeography]]|volume=11|issue=3|doi=10.21425/F5FBG43862|s2cid=204900275 |doi-access=free}}</ref>  Other areas have shown increases in some insect species, although trends in most regions are currently unknown. It is difficult to assess long-term trends in insect abundance or diversity because historical measurements are generally not known for many species. Robust data to assess at-risk areas or species is especially lacking for arctic and tropical regions and a majority of the southern hemisphere.<ref name=FAQEntSocAm2019/>

In March 2019 Chris D. Thomas and other scientists wrote in response to the apocalyptic "Insectageddon" predictions of Sánchez-Bayo, "we respectfully suggest that accounts of the demise of insects may be slightly exaggerated". They called for "joined-up thinking" in responding to insect declines, backed up by more robust data than were currently available.<ref name="Thomas2019" />

==Causes ==

=== Destruction and pollution ===
The causes of the declines in insect populations, and their relative importance, are not fully understood. They are likely to vary between different insect groups and geographical regions.<ref>{{Cite journal|last=Wagner|first=David L.|date=2020-01-07|title=Insect Declines in the Anthropocene|journal=Annual Review of Entomology|volume=65|issue=1|pages=457–480|doi=10.1146/annurev-ento-011019-025151|pmid=31610138 |s2cid=204702504 |issn=0066-4170|doi-access=free}}</ref> A study placed these causes in the order of importance as follows: "(i) [[Earth:Habitat destruction|habitat loss]] and conversion to intensive agriculture and [[Earth:Urbanization|urbanisation]]; ii) pollution,<ref>{{cite journal |last1=Eggleton |first1=Paul |year=2020 |title=The State of the World's Insects |journal=Annual Review of Environment and Resources |volume=45 |pages=61–82 |doi=10.1146/annurev-environ-012420-050035 |doi-access=free}}</ref> mainly that by synthetic pesticides and fertilisers; iii) biological factors, including pathogens and introduced species; and iv) climate change."<ref>{{Cite journal |last=Sánchez-Bayo |first=Francisco |last2=Wyckhuys |first2=Kris A.G. |date=2019 |title=Worldwide decline of the entomofauna: A review of its drivers |url=https://linkinghub.elsevier.com/retrieve/pii/S0006320718313636 |journal=Biological Conservation |language=en |volume=232 |pages=8–27 |doi=10.1016/j.biocon.2019.01.020}}</ref> 

[[Astronomy:Light pollution|Light pollution]] also plays a role.<ref name="OwensLewis2018" /><ref>[https://www.theguardian.com/environment/2019/nov/22/light-pollution-insect-apocalypse Light pollution is key 'bringer of insect apocalypse'] The Guardian, 2019</ref><ref>{{Cite journal |last1=Boyes |first1=Douglas H. |last2=Evans |first2=Darren M. |last3=Fox |first3=Richard |last4=Parsons |first4=Mark S. |last5=Pocock |first5=Michael J. O. |date=August 2021 |title=Street lighting has detrimental impacts on local insect populations |journal=Science Advances |language=EN |volume=7 |issue=35 |bibcode=2021SciA....7.8322B |doi=10.1126/sciadv.abi8322 |pmc=8386932 |pmid=34433571}}</ref> Other factors that are thought to be important are [[Earth:Introduced species|introduced species]]<ref name="Wagner2010" /><ref name="Sánchez-Bayo2019" /> and [[Earth:Eutrophication|eutrophication]] from fertilisers. 

The use of increased quantities of [[Biology:Insecticide|insecticide]]s and [[Biology:Herbicide|herbicide]]s on crops have affected not only non-target insect species, but also the plants on which they feed. 

For example, a review in 2017 commented on a large study in Germany about insect population decline as follows: "The authors of the German study were not able to link the observed decline to climate change or pesticide use; although agricultural intensification and the practices associated with it, were, however, suggested as likely to be involved in some way."<ref name=Leather2017/>

===Climate change===
Climate change and the introduction of exotic species (see [[Earth:Climate change and invasive species|climate change and invasive species]]) that compete with the [[Biology:Indigenous (ecology)|indigenous]] ones put the native species under stress, and as a result they are more likely to succumb to pathogens and parasites.<ref name="Reckhaus2017" /> Plants grow faster in presence of increased CO<sub>2</sub> (due to the [[Earth:CO2 fertilization effect|CO<sub>2</sub> fertilisation effect]]) but the resulting plant biomass contains fewer nutrients.<ref>{{cite journal |last1=Welti |first1=Ellen A. R. |last2=Roeder |first2=Karl A. |last3=Beurs |first3=Kirsten M. de |last4=Joern |first4=Anthony |last5=Kaspari |first5=Michael |title=Nutrient dilution and climate cycles underlie declines in a dominant insect herbivore |journal=Proceedings of the National Academy of Sciences |date=31 March 2020 |volume=117 |issue=13 |pages=7271–7275 |doi=10.1073/pnas.1920012117 |pmid=32152101 |pmc=7132292 |bibcode=2020PNAS..117.7271W |language=en |issn=0027-8424|doi-access=free }}</ref> While some species such as flies and [[Biology:Cockroach|cockroach]]es might increase as a result,<ref name="Sánchez-Bayo2019" /> the total [[Earth:Biomass (ecology)|biomass]] of insects is estimated to be decreasing by between about 0.9 to 2.5% per year.<ref name="MainNatGeographic14Feb2019" /><ref name="vanKlink2020" />

{{excerpt|Extinction risk from climate change#Insects|paragraphs=1-3|file=no}}

== Consequences ==
[[File:00_1680_Bumblebee.gif|thumb|Bumblebee collecting pollen.]]
Insect population decline affects ecosystems, and other animal populations, including [[Humans|humans]]. Insects are at "the structural and functional base of many of the world's ecosystems."<ref name="Sánchez-Bayo2019" /> A 2019 global review warned that, if not mitigated by decisive action, the decline would have a catastrophic impact on the planet's ecosystems.<ref name="Sánchez-Bayo2019" /> Birds and larger mammals that eat insects can be directly affected by the decline. Declining insect populations can reduce the [[Biology:Ecosystem services|ecosystem services]] provided by beneficial bugs, such as [[Biology:Pollination|pollination]] of agricultural crops, and biological waste disposal.<ref name="MainNatGeographic14Feb2019" /> 

According to the [[Organization:Zoological Society of London|Zoological Society of London]], in addition to such loss of instrumental value, the decline also represents a loss of the declining species' [[Philosophy:Intrinsic value (ethics)|intrinsic value]].<ref name="ZSL" />

==Methodology==
Three principal metrics are used to capture and report on insect declines:
* ''Abundance'' – simply put the numerical total of individual insects. Depending on context, it can refer to the number of insects in a particular assembly, in a geographical area, or the sum total of insects globally  (regardless of which species the individuals belong to).
* ''Biomass'' – the total weight of insects (again regardless of species).
* ''Biodiversity'' – the number of extant insect species. Depending on context, a reduction in biodiversity can mean certain species of insects have vanished locally, though it may mean species have gone totally extinct across the entire planet.<ref name=WagnerJ2020/><ref name=vanKlink2020/><ref name="Sánchez-Bayo2019"/>

Most of the individual studies tracking insect declines report just abundance, others just on biomass, some on both, and yet others report on all three metrics. Data directly related to diversity loss at global level is more sparse than for abundance or biomass declines. Estimates for diversity loss at a planetary level tend to involve extrapolating from abundance or biomass data; while studies sometimes show local extirpation of an insect species, actual world wide extinctions are challenging to discern. In a 2019 review, David Wagner noted that currently the [[Earth:Holocene extinction|Holocene extinction]] is seeing animal species loss at about  100–1,000 times the planet's normal background rate, and that various studies found a similar, or possibly even faster extinction rate for insects. Wagner opines that serious though this [[Biology:Biodiversity loss|biodiversity loss]] is, it is the decline in abundance that will have the most serious ecological impact.<ref name=WagnerJ2020/><ref name=vanKlink2020/><ref name="Sánchez-Bayo2019"/><ref name=Dirzo2014/>

In theory it is possible for the three metrics to be independent. For instance, a decline in biomass might not involve a decrease in abundance or diversity if all that was happening was that typical insects were getting smaller. In practice though,  abundance and biomass tend to be closely related, typically showing a similar level of decline. Change in biodiversity is often, though not always,
directly proportional to the other two metrics.<ref name=vanKlink2020/><ref name="Sánchez-Bayo2019"/> Some studies find cases where, in certain locations, change in biodiversity is inversely proportional to the other metrics. For example, a 42 year study of insects in the pristine Breitenbach stream near Schlitz, which is believed to have been unaffected by anthropogenic decline related causes except for climate change, found that while abundance of insects decreased, biodiversity actually rose, especially during the first half of the study.<ref name= Baranov2020/>

== Global studies ==
[[File:Percent of insect species.svg|thumb|Insects with population trends documented by the [[Organization:International Union for Conservation of Nature|International Union for Conservation of Nature]], for orders Collembola, Hymenoptera, Lepidoptera, Odonata, and Orthoptera.]]A 2020 meta-analysis found that globally terrestrial insects appear to be declining in abundance at a rate of about 9% per decade, while the abundance of freshwater insects appears to be increasing by 11% per decade. The study analysed 166 long-term studies, involving 1676 different sites across the world. It found considerable variations in insect decline depending on locality – the authors considered this a hopeful sign, as it suggests local factors, including conservation efforts, can make a big difference. The article stated that the increase in freshwater insects may in part be due to efforts to clean up lakes and rivers, and may also relate to global warming and enhanced primary productivity driven by increased nutrient inputs.<ref name="vanKlink2020" />  However, the data selection and methodology of the article were criticised in several publications.<ref name="Desquilbet2020">{{Cite journal |last1=Desquilbet |first1=Marion |last2=Gaume |first2=Laurence |last3=Grippa |first3=Manuela |last4=Céréghino |first4=Régis |last5=Humbert |first5=Jean-François |last6=Bonmatin |first6=Jean-Marc |last7=Cornillon |first7=Pierre-André |last8=Maes |first8=Dirk |last9=Dyck |first9=Hans Van |last10=Goulson |first10=David |date=2020-12-18 |title=Comment on 'Meta-analysis reveals declines in terrestrial but increases in freshwater insect abundances' |journal=Science |volume=370 |issue=6523 |pages=eabd8947 |doi=10.1126/science.abd8947 |issn=0036-8075 |pmid=33335036 |doi-access=free}}</ref><ref name="Jähnig2021">{{cite journal |last1=Jähnig |first1=Sonja C. |last2=et. |first2=al. |year=2021 |title=Revisiting global trends in freshwater insect biodiversity |journal=Wiley Interdisciplinary Reviews: Water |volume=8 |issue=2 |doi=10.1002/wat2.1506 |doi-access=free|hdl=1885/275614 |hdl-access=free }}</ref>

In 2022, 66 researchers conducted a survey of 3331 biodiversity experts (meaning scientists who published a study on the subject of biodiversity over the past decade). This included 629 experts in terrestrial and freshwater [[Biology:Invertebrate|invertebrate]]s: on average, they believed that around 30% (with an uncertainty range between 20 and 50%) of these species are or have been threatened with extinction (including the species which had already gone extinct since 1500).  As insects account for the vast majority of the world's invertebrates, this figure by extension applies to them as well.<ref name="Isbell2022">{{Cite journal |last1=Isbell |first1=Forest |last2=Balvanera |first2=Patricia |last3=Mori |first3=Akira S |last4=He |first4=Jin-Sheng |last5=Bullock |first5=James M |last6=Regmi |first6=Ganga Ram |last7=Seabloom |first7=Eric W |last8=Ferrier |first8=Simon |last9=Sala |first9=Osvaldo E |last10=Guerrero-Ramírez |first10=Nathaly R |last11=Tavella |first11=Julia |last12=Larkin |first12=Daniel J |last13=Schmid |first13=Bernhard |last14=Outhwaite |first14=Charlotte L |last15=Pramual |first15=Pairot |date=18 July 2022 |title=Expert perspectives on global biodiversity loss and its drivers and impacts on people |url=https://esajournals.onlinelibrary.wiley.com/doi/10.1002/fee.2536 |journal=Frontiers in Ecology and the Environment |language=en |volume=21 |issue=2 |pages=94–103 |doi=10.1002/fee.2536 |s2cid=250659953 |hdl-access=free |last16=Borer |first16=Elizabeth T |last17=Loreau |first17=Michel |last18=Crossby Omotoriogun |first18=Taiwo |last19=Obura |first19=David O |last20=Anderson |first20=Maggie |last21=Portales-Reyes |first21=Cristina |last22=Kirkman |first22=Kevin |last23=Vergara |first23=Pablo M |last24=Clark |first24=Adam Thomas |last25=Komatsu |first25=Kimberly J |last26=Petchey |first26=Owen L |last27=Weiskopf |first27=Sarah R |last28=Williams |first28=Laura J |last29=Collins |first29=Scott L |last30=Eisenhauer |first30=Nico |last31=Trisos |first31=Christopher H |last32=Renard |first32=Delphine |last33=Wright |first33=Alexandra J |last34=Tripathi |first34=Poonam |last35=Cowles |first35=Jane |last36=Byrnes |first36=Jarrett EK |last37=Reich |first37=Peter B |last38=Purvis |first38=Andy |last39=Sharip |first39=Zati |last40=O’Connor |first40=Mary I |last41=Kazanski |first41=Clare E |last42=Haddad |first42=Nick M |last43=Soto |first43=Eulogio H |last44=Dee |first44=Laura E |last45=Díaz |first45=Sandra |last46=Zirbel |first46=Chad R |last47=Avolio |first47=Meghan L |last48=Wang |first48=Shaopeng |last49=Ma |first49=Zhiyuan |last50=Liang |first50=Jingjing Liang |last51=Farah |first51=Hanan C |last52=Johnson |first52=Justin Andrew |last53=Miller |first53=Brian W |last54=Hautier |first54=Yann |last55=Smith |first55=Melinda D |last56=Knops |first56=Johannes MH |last57=Myers |first57=Bonnie JE |last58=Harmáčková |first58=Zuzana V |last59=Cortés |first59=Jorge |last60=Harfoot |first60=Michael BJ |last61=Gonzalez |first61=Andrew |last62=Newbold |first62=Tim |last63=Oehri |first63=Jacqueline |last64=Mazón |first64=Marina |last65=Dobbs |first65=Cynnamon |last66=Palmer |first66=Meredith S |hdl=10852/101242}}</ref>

A 2019 survey of 24 entomologists working on six continents found that on a scale of 0 to 10, with 10 being the worst, all the scientists rated the severity of the insect decline crisis as being between 8–10.<ref name="Hance2019" />

=== Global assessment report on biodiversity and ecosystem services ===

The Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services reported its assessment of global biodiversity in 2019.  Its summary for insect life was that "Global trends in insect populations are not known but rapid declines have been well documented in some places.&nbsp;... Local declines of insect populations such as wild bees and butterflies have often been reported, and insect abundance has declined very rapidly in some places even without large-scale land-use change, but the global extent of such declines is not known.&nbsp;... The proportion of insect species threatened with extinction is a key uncertainty, but available evidence supports a tentative estimate of 10 per cent."<ref name="IPBES" /> In 2022, some researchers had expressed concern about the apparent mismatch between this tentative IPBES estimate, and that of 629 experts on invertebrate biodiversity they surveyed, which was closer to 30%. They argued that more investigations into insects and other "hyperdiverse and understudied taxa" are urgently required to clarify the matter.<ref name="Isbell2022" />  

== Survey results for specific regions ==

===United Kingdom===
The Rothamsted Insect Survey at [[Earth:Rothamsted Research|Rothamsted Research]], Harpenden, England, began monitoring insect suction traps across the UK in 1964. According to the group, these have produced "the most comprehensive standardised long-term data on insects in the world".<ref>{{cite web |title=About The Insect Survey |url=https://insectsurvey.com/about |publisher=Rothamsted Research}}</ref> The traps are "effectively upside-down [[Physics:Vacuum cleaner|Hoovers]] running 24/7, continually sampling the air for migrating insects", according to James Bell, the survey leader, in an interview in 2017 with the journal ''Science''. Between 1970 and 2002, the insect biomass caught in the traps declined by over two-thirds in southern Scotland, although it remained stable in England. The scientists speculate that insect abundance was already lost in England by 1970 (figures in Scotland were higher than in England when the survey began), or that [[Biology:Aphid|aphid]]s and other pests increased there in the absence of their insect predators.<ref name="Vogel2017" />

A 2014 review noted: "Of all insects with [[Organization:International Union for Conservation of Nature|IUCN]]-documented population trends [203 insect species in five orders], 33% are declining, with strong variation among orders." In the UK, "30 to 60% of species per order have declining ranges". Insect pollinators, "needed for 75% of all the world's food crops", appear to be "strongly declining globally in both abundance and diversity", which has been linked in Northern Europe to the decline of plant species that rely on them. The study referred to the human-caused loss of [[Biology:Vertebrate|vertebrate]]s and invertebrates as the "Anthropocene [[Earth:Defaunation|defaunation]]".<ref name="Dirzo2014" /><ref name="JarvisNYT27Nov2018" />

Anecdotal evidence for insect decline has been offered by those who recall apparently greater insect abundance in the 20th century. Entomologist Simon Leather recalls that, in the 1970s, windows of Yorkshire houses he visited on his early-morning paper round would be "plastered with tiger moths" attracted by the house's lighting during the night. [[Biology:Arctiinae (moth)|Tiger moths]] have now largely disappeared from the area.<ref name="McKieObserver17June2018" /> Another anecdote is recalled by environmentalist Michael McCarthy concerning the vanishing of the "moth snowstorms", a relatively common sight in the UK in the 1970s and earlier. Moth snowstorms occurred when moths congregated with such density that they could appear like a blizzard in the beam of automobile headlights.<ref name="McCarthyGuardian21Oct2017" />

In 2004 the Royal Society for the Protection of Birds organised a Big Bug Count, issuing "splatometers" to about 40,000 volunteers to help count the number of insects colliding with their [[Vehicle registration plate|number plate]]s. They found an average of one insect per 5 miles (8&nbsp;km), which was less than expected.<ref name="KnaptonTelegraph17June2018" /><ref name="BBC04" />

===Germany{{anchor|Krefeld}}===
[[File:Malaise trap, Germany.jpg|thumb|left|[[Engineering:Malaise trap|Malaise trap]]s in German nature reserves<ref name="Hallmann2017PLoS" />]]

In 2013 the Krefeld Entomological Society reported a "huge reduction in the biomass of insects"<ref name="Leather2017" /> caught in [[Engineering:Malaise trap|malaise trap]]s in 63 nature reserves in Germany (57 in Nordrhein-Westfalen, one in Rheinland-Pfalz and one in Brandenburg).<ref name="Sorg2013" /><ref name="Bundestag2017p5">{{cite web |title=Zum Insektenbestand in Deutschland: Reaktionen von Fachpublikum und Verbänden auf eine neue Studie |url=https://www.bundestag.de/resource/blob/536702/5537cc08d8f54d93ac042fb36bde811e/wd-8-039-17-pdf-data.pdf |publisher=Wissenschaftliche Dienste, Deutscher Bundestag (German parliament) |date=13 November 2017 |page=5 |ref = {{sfnref|Deutscher Bundestag|2017}} }}</ref> A reanalysis published in 2017 suggested that, in 1989–2016, there had been a "seasonal decline of 76%, and mid-summer decline of 82%, in flying insect biomass over the 27 years of study". The decline was "apparent regardless of habitat type" and could not be explained by "changes in weather, land use, and habitat characteristics". The authors suggested that not only butterflies, moths and wild bees appear to be in decline, as previous studies indicated, but "the flying insect community as a whole".<ref name="Hallmann2017PLoS" /><ref name="Leather2017" /><ref name="Nature18Oct2017" /><ref name="Guarino18Oct2017" /><ref name="StagerNYT26May2018" />

Scientists stated in 2019: "In 2017, a 27-year long population monitoring study revealed a shocking 76% decline in flying insect biomass at several of Germany's protected areas (Hallmann et al., 2017). This represents an average 2.8% loss in insect biomass per year in habitats subject to rather low levels of human disturbance, which could either be undetectable or regarded statistically non-significant if measurements were carried out over shorter time frames. Worryingly, the study shows a steady declining trend over nearly three decades."<ref name="Sánchez-Bayo2019" />

According to ''[[Finance:The Economist|The Economist]]'', the study was the "third most frequently cited scientific study (of all kinds) in the media in 2017". It "pushed the governments of Germany and the Netherlands into setting up programmes to protect insect diversity."<ref name="Economist23March2019" /> The British entomologist Simon Leather said that he hoped media reports, following the study, of an "ecological Armageddon" had been exaggerated; he argued that the Krefeld and other studies should be a wake-up call, and that more funding is needed to support long-term studies.<ref name="Leather2017" /><ref name="DCGuardian18Oct2017" /><ref name="McGraneNYT4Dec2017" /> The Krefeld study's authors were not able to link the decline to climate change or pesticides, he wrote, but they suggested that intensive farming was involved. While agreeing with their conclusions, he cautioned that "the data are based on biomass, not species, and the sites were not sampled continuously and are not globally representative".

=== Puerto Rico ===
A 2018 study of the El Yunque National Forest in Puerto Rico reported a decline in [[Biology:Arthropod|arthropod]]s, and in lizards, frogs, and birds ([[Biology:Insectivore|insect-eating]] species) based on measurements in 1976 and 2012.<ref name="Lister2018" /><ref name="Sánchez-Bayo2019" /> The American entomologist David Wagner called the study a "clarion call" and "one of the most disturbing articles" he had ever read.<ref name="Guarino15Oct2018" /> The researchers reported "biomass losses between 98% and 78% for ground-foraging and canopy-dwelling arthropods over a 36-year period, with respective annual losses between 2.7% and 2.2%".<ref name="Sánchez-Bayo2019" /> The decline was attributed to a rise in the average temperature; tropical insect species cannot tolerate a wide range of temperatures.<ref name="Lister2018" /><ref name="Sánchez-Bayo2019" /><ref name="MainNatGeographic14Feb2019" /> The researchers were shocked by the results: "We couldn't believe the first results. I remember [in the 1970s] butterflies everywhere after rain. On the first day back [in 2012], I saw hardly any."<ref name="Economist23March2019" />

===Netherlands ===
In 2019 a study of butterfly numbers in the Netherlands from 1890 to 2017 reported an estimated decline of 84 percent. When analysed by type of habitat, the trend was found to have stabilised in [[Earth:Grassland|grassland]] and [[Biology:Woodland|woodland]] in recent decades but the decline continued in heathland. The decline was attributed to changes in land use due to more efficient farming methods, which has caused a decline in weeds. The recent up-tick in some populations documented in the study was attributed to (conservationist) changes in land management and thus an increase in suitable habitat.<ref name="vanStrien2019" /><ref name="CBS29March2019">{{cite web |title=Over 80% decline in butterflies since late 1800s |url=https://www.cbs.nl/nl-nl/nieuws/2019/13/ruim-80-procent-minder-vlinders-dan-eind-19e-eeuw |publisher=Statistics Netherlands (Centraal Bureau voor de Statistiek |archive-url=https://web.archive.org/web/20190330114126/https://www.cbs.nl/nl-nl/nieuws/2019/13/ruim-80-procent-minder-vlinders-dan-eind-19e-eeuw |archive-date=30 March 2019 |date=29 March 2019|url-status=live}}</ref><ref name="Telegraaf29March2019">{{cite news |title=Veel minder vlinders |url=https://www.telegraaf.nl/nieuws/3364801/veel-minder-vlinders |work=De Telegraaf |date=29 March 2019 |access-date=14 April 2019 |archive-date=28 April 2022 |archive-url=https://web.archive.org/web/20220428064838/https://www.telegraaf.nl/nieuws/3364801/veel-minder-vlinders |url-status=dead }}</ref><ref name="Barkham2019" /> 

=== Switzerland ===
A report by the Swiss Academy of Natural Sciences in April 2019 reported that 60 percent of the insects that had been studied in Switzerland were at risk, mostly in farming and aquatic areas; that there had been a 60 percent decline in insect-eating birds since 1990 in rural areas; and that urgent action was needed to address the causes.<ref name="SWI" /><ref name="SANS" />

===United States and Western Europe {{anchor|Sánchez-Bayo}}===
[[File:SympetrumInfuscatum.jpg|thumb|Except for taxa regarded as beneficial or charismatic, such as the pictured dragonfly, there is relatively little population decline data available for specific insect species.]]
A 2019 review analysed 73 long-term insect surveys that had shown decline, most of them in the United States and Western Europe.<ref name="Sánchez-Bayo2019" /><ref>[https://ars.els-cdn.com/content/image/1-s2.0-S0006320718313636-gr1_lrg.jpg "Fig. 1. Geographic location of the 73 reports studied on the world map"], Sánchez-Bayo and Wyckhuys 2019.</ref> While noting population increases for certain species of insects in particular areas, the authors reported an annual 2.5% loss of biomass. They wrote that the review "revealed dramatic rates of decline that may lead to the extinction of 40% of the world's insect species over the next few decades",<ref name="Sánchez-Bayo2019" /><ref name="LePageNewScientist11Feb2019" /> a conclusion that was challenged.<ref name="Wagner2019" /><ref name="Simmons2019" /> They did note the review's limitations, namely that the studies were largely concentrated on popular insect groups (butterflies and moths, bees, dragonflies and beetles); few had been done on groups as [[Biology:Diptera|Diptera]] (flies), [[Biology:Orthoptera|Orthoptera]] (which includes [[Biology:Grasshopper|grasshopper]]s and [[Biology:Cricket (insect)|cricket]]s), and [[Biology:Hemiptera|Hemiptera]] (such as [[Biology:Aphid|aphid]]s); data from the past from which to calculate trends is largely unavailable; and the data that does exist mostly relates to Western Europe and North America, with the tropics and southern hemisphere (major insect habitats) under-represented.<ref name="Sánchez-Bayo2019" /><ref name="DCObserver10Feb2019" />

The methodology and strong language of the review were questioned.<ref name="Wagner2019" /><ref name="Simmons2019" /><ref name="Sanders16Feb2019" /> Other criticism included that the authors attributed the decline to particular threats based on the studies they reviewed, even when those studies had simply suggested threats rather than clearly identifying them.<ref name="Simmons2019" /> Some reviewers said the study might underestimate the rate of insect decline in the tropics.<ref name="LePageNewScientist11Feb2019" /> Some reviewers also had concerns about the review's search terms, geographic biases, calculations of extinction rates, and inaccurate assessment of drivers of population change. Nevertheless, they found that while it was "a useful review of insect population ''declines'' in North America and Europe, it should not be used as evidence of global insect population ''trends'' and threats."<ref name="Simmons2019" />

In a 2020 paper that studied insects and other arthropods across all Long-term Ecological Research (LTER) sites in the U.S., the authors found some declines, some increases, but generally few consistent losses in arthropod abundance or diversity. This study found some variation in location, but generally stable numbers of insects. As noted in the paper, the authors did not do any ''a priori'' selection of arthropod taxa. Instead, they tested the hypothesis that if the arthropod decline was pervasive, it would be detected in monitoring programs not originally designed to look for declines. They suggest that overall numbers of insects vary but overall show no net change.<ref>{{cite journal |last1=Crossley |first1=Michael |date=10 August 2020 |title=No net insect abundance and diversity declines across US Long Term Ecological Research sites |url=https://www.nature.com/articles/s41559-020-1269-4 |journal=Nature Ecology and Evolution |volume=4 |issue=10 |pages=1368–1376 |doi=10.1038/s41559-020-1269-4 |pmid=32778751 |s2cid=221099483 |access-date=11 August 2020}}</ref> However, the methodology of the article was criticised because it failed to account for changes in sampling location and sampling effort at LTER sites and for the impact of experimental conditions, had inconsistencies in the database constitution and relied on an inadequate statistical analysis.<ref>Welti, E.A.R., Joern, A., Ellison, A.M. et al. [https://www.nature.com/articles/s41559-021-01424-0#citeas Studies of insect temporal trends must account for the complex sampling histories inherent to many long-term monitoring efforts]. ''Nature Ecology and Evolution'' '''5''' 589–591 (2021). {{doi|10.1038/s41559-021-01424-0}}</ref><ref>{{cite journal |last1=Desquilbet |first1=Marion |last2=Cornillon |first2=Pierre-André |last3=Gaume |first3=Laurence |last4=Bonmatin |first4=Jean-Marc |year=2021 |title=Adequate statistical modelling and data selection are essential when analysing abundance and diversity trends |url=http://publications.ut-capitole.fr/43237/1/articles/s41559-021-01427-x.epdf_sharing_token%3DtDqmFjgCiz4n48ij_fI079RgN0jAjWel9jnR3ZoTv0O4mO5CkzfI-WdkSWvtSxayB2To9R1gzYOnve4_aEe4G8rqfGbOk0XrGRUQlGA03a6cVB3e3UP2cPmJ4vZ19RirZFY_MEwFEIuxiGzghVmUfF1WXdY390OkC8nJZo7-xzU%3D |journal=Nature Ecology & Evolution |volume=5 |issue=5 |pages=592–594 |doi=10.1038/s41559-021-01427-x |pmid=33820967 |s2cid=233037619}}</ref>[[File:Windshield phenomenon, Australia, March 2009 (2).jpg|thumb|left|Bug splats, New South Wales, 2009]]
The [[Biology:Windshield phenomenon|windshield phenomenon]] – car windscreens covered in dead insects after even a short drive through a rural area in Europe and North America – seems also largely to have disappeared; in the 21st century, drivers find they can go an entire summer without noticing it.<ref name="Vogel2017" /><ref name="KnaptonTelegraph17June2018" /> John Rawlins, head of invertebrate zoology at the Carnegie Museum of Natural History, speculated in 2006 that more aerodynamic car designs could explain the change.<ref name="LinnPost-Gazette4June2006" /> Entomologist Martin Sorg told ''Science'' in 2017: "I drive a Land Rover, with the aerodynamics of a refrigerator, and these days it stays clean."<ref name="Vogel2017" /> Rawlins added that land next to high-speed highways has become more manicured and therefore less attractive to insects.<ref name="LinnPost-Gazette4June2006" />
== Countermeasures ==

=== Overall policies and conventions ===
The most influential factors, that can be counteracted, are habitat loss and degradation, pesticide use, and climate change. Policies at all levels of government across the globe are required to address these in a meaningful way.<ref name="10.1111/csp2.80">{{cite journal |last1=Forister |first1=Matthew L. |last2=Pelton |first2=Emma M. |last3=Black |first3=Scott H. |date=2019 |title=Declines in insect abundance and diversity: We know enough to act now |journal=Conservation Science and Practice |language=en |volume=1 |issue=8 |pages=e80 |doi=10.1111/csp2.80 |issn=2578-4854 |s2cid=196681430 |doi-access=free}}</ref>

Much of the world's efforts to retain biodiversity at national level is reported to the United Nations as part of the [[Biology:Convention on Biological Diversity|Convention on Biological Diversity]]. Reports typically describe policies to prevent the loss of diversity generally, such as habitat preservation, rather than specifying measures to protect particular taxa. Pollinators are the main exception to this, with several countries reporting efforts to reduce the decline of their pollinating insects.<ref name="FAO2019" />

Following the 2017 Krefeld and other studies, Germany's environment ministry, the BMU, started an ''Action Programme for Insect Protection'' (''Aktionsprogramm Insektenschutz'').<ref name="FAO2019" /> Their goals include promoting insect habitats in the agricultural landscape, and reducing pesticide use, [[Astronomy:Light pollution|light pollution]], and pollutants in soil and water.<ref name="BMU" /> 

=== Reduction of pesticide-use ===
Beyond halting habitat loss and fragmentation and [[Earth:Climate change mitigation|limiting climate change]], reducing pesticide use is required for preserving insect populations.<ref>{{cite journal |last1=Basset |first1=Yves |last2=Lamarre |first2=Greg P. A. |date=28 June 2019 |title=Toward a world that values insects |journal=Science |language=EN |volume=364 |issue=6447 |pages=1230–1231 |bibcode=2019Sci...364.1230B |doi=10.1126/science.aaw7071 |pmid=31249044 |s2cid=195750374 |doi-access=free}}</ref> Pesticides have been found far from their application source and legislatively mandated elimination of cosmetic pesticide use, as well as general reductions of pesticide use, could greatly benefit insects.<ref name="10.1073/pnas.2002547117" /> Organic food/farming-related measures can be solutions.<ref name="10.1111/csp2.80" />

However, some scientists warned that excessive focus on reducing pesticide use could be counterproductive as pests already cause a 35 percent yield loss in crops, which can rise to 70 percent if pesticides are not used. If the yield loss was compensated for by expanding agricultural land with deforestation and other habitat destruction, it could exacerbate insect decline.<ref name="Thomas2019" /><!--not clear what this refers to: Citing a 2010 warning from [[Biography:Robert May, Baron May of Oxford|Lord May]], the authors of the 2019 worldwide review suggest decisive action is needed "to avert a catastrophic collapse of nature's [[Earth:Ecosystem|ecosystem]]s."<ref name=Sánchez-Bayo2019/>-->

=== Wildflower strips and buffer zones ===
[[File:Mechtenberg2009.jpg|thumb|A flowering strip with cornflower dominance between cereal fields as a field trial in Germany]]
A [[Earth:Wildflower strip|wildflower strip]] is a strip of land sown with seeds of biodiverse<!-- unmaintained--> insect- and pollinator-friendly flowering plant species, usually at the edge of an agricultural field, intended to sustain local [[Biology:Biodiversity|biodiversity]], conserve insects, restore farmland birds and counteract the negative consequences of agricultural intensification.<ref>{{cite journal |last1=Haaland |first1=Christine |last2=Naisbit |first2=Russell E. |last3=Bersier |first3=Louis-Félix |title=Sown wildflower strips for insect conservation: a review |journal=Insect Conservation and Diversity |date=2011 |volume=4 |issue=1 |pages=60–80 |doi=10.1111/j.1752-4598.2010.00098.x |s2cid=55210072 |language=en |issn=1752-4598|url=http://doc.rero.ch/record/28343/files/ber_sws.pdf }}</ref><ref>{{cite journal |last1=Ganser |first1=Dominik |last2=Mayr |first2=Barbara |last3=Albrecht |first3=Matthias |last4=Knop |first4=Eva |title=Wildflower strips enhance pollination in adjacent strawberry crops at the small scale |journal=Ecology and Evolution |date=December 2018 |volume=8 |issue=23 |pages=11775–11784 |doi=10.1002/ece3.4631 |pmid=30598775 |pmc=6303775 |issn=2045-7758}}</ref><ref>{{cite journal |last1=Schmidt |first1=Annika |last2=Fartmann |first2=Thomas |last3=Kiehl |first3=Kathrin |last4=Kirmer |first4=Anita |last5=Tischew |first5=Sabine |title=Effects of perennial wildflower strips and landscape structure on birds in intensively farmed agricultural landscapes |journal=Basic and Applied Ecology |date=1 February 2022 |volume=58 |pages=15–25 |doi=10.1016/j.baae.2021.10.005 |s2cid=240256023 |language=en |issn=1439-1791|doi-access=free }}</ref><ref>{{cite journal |last1=Grass |first1=Ingo |last2=Albrecht |first2=Jörg |last3=Farwig |first3=Nina |last4=Jauker |first4=Frank |title=Plant traits and landscape simplification drive intraspecific trait diversity of Bombus terrestris in wildflower plantings |journal=Basic and Applied Ecology |date=1 December 2021 |volume=57 |pages=91–101 |doi=10.1016/j.baae.2021.10.002 |s2cid=240241322 |language=en |issn=1439-1791|doi-access=free }}</ref>

Buffer-zones around nature reserves where pesticide-use is drastically reduced has been proposed for inclusion in the countermeasures. Scientists who proposed the measure conducted a Germany-wide field study and found that insect samples in these areas are contaminated with ~16 pesticides on average, proportionate to the agricultural production area in a radius of 2 km.<ref>{{cite journal |last1=Brühl |first1=Carsten A. |last2=Bakanov |first2=Nikita |last3=Köthe |first3=Sebastian |last4=Eichler |first4=Lisa |last5=Sorg |first5=Martin |last6=Hörren |first6=Thomas |last7=Mühlethaler |first7=Roland |last8=Meinel |first8=Gotthard |last9=Lehmann |first9=Gerlind U. C. |date=16 December 2021 |title=Direct pesticide exposure of insects in nature conservation areas in Germany |journal=Scientific Reports |language=en |volume=11 |issue=1 |pages=24144 |bibcode=2021NatSR..1124144B |doi=10.1038/s41598-021-03366-w |issn=2045-2322 |pmc=8677746 |pmid=34916546}}</ref>

=== Wildlife gardens ===
{{Further|Biology:Wildlife garden}}
The Entomological Society of America suggests that people maintain plant diversity in their gardens and leave "natural habitat, like leaf litter and dead wood".<ref name=FAQEntSocAm2019/> The Xerces Society in the U.S. has been doing a Western Monarch Thanksgiving Count which includes observations from volunteers for 22 years.<ref>{{cite web |title=Record Low Number of Overwintering Monarch Butterflies in California—They Need Your Help! |url=https://xerces.org/2019/01/17/record-low-overwintering-monarchs-in-california/ |website=Xerces Society}}</ref>

It has been suggested that "Because many insects need little space to survive, even partial conversion of [[Earth:Lawn|lawn]]s to minimally disturbed natural vegetation—say 10%—could significantly aid insect conservation, while simultaneously lowering the cost of lawn maintenance".<ref name="10.1073/pnas.2002547117">{{cite journal |last1=Kawahara |first1=Akito Y. |last2=Reeves |first2=Lawrence E. |last3=Barber |first3=Jesse R. |last4=Black |first4=Scott H. |title=Opinion: Eight simple actions that individuals can take to save insects from global declines |journal=Proceedings of the National Academy of Sciences |date=12 January 2021 |volume=118 |issue=2 |doi=10.1073/pnas.2002547117 |pmid=33431563 |pmc=7812750 |language=en |issn=0027-8424|doi-access=free }}</ref>

=== Awareness raising ===
In the UK, 27 ecologists and entomologists signed an open letter to ''{{wipe|The Guardian}}'' in March 2019, calling on the British research establishment to investigate the decline. Signatories included Simon Leather, Stuart Reynolds (former president of the Royal Entomological Society), John Krebs and John Lawton (both former presidents of the Natural Environment Research Council), [[Biography:Paul Brakefield|Paul Brakefield]], George McGavin, Michael Hassell, Dave Goulson, Richard Harrington (editor of the Royal Entomological Society's magazine, ''Antenna''), Kathy Willis and Jeremy Thomas.<ref name="Leather2019" />

More media coverage has been proposed.<ref>{{cite journal |last1=Samways |first1=Michael J. |last2=Barton |first2=Philip S. |last3=Birkhofer |first3=Klaus |last4=Chichorro |first4=Filipe |last5=Deacon |first5=Charl |last6=Fartmann |first6=Thomas |last7=Fukushima |first7=Caroline S. |last8=Gaigher |first8=René |last9=Habel |first9=Jan C. |last10=Hallmann |first10=Caspar A. |last11=Hill |first11=Matthew J. |last12=Hochkirch |first12=Axel |last13=Kaila |first13=Lauri |last14=Kwak |first14=Mackenzie L. |last15=Maes |first15=Dirk |date=1 February 2020 |title=Solutions for humanity on how to conserve insects |journal=Biological Conservation |language=en |volume=242 |pages=108427 |doi=10.1016/j.biocon.2020.108427 |issn=0006-3207 |s2cid=213927925 |doi-access=free |last16=Mammola |first16=Stefano |last17=Noriega |first17=Jorge A. |last18=Orfinger |first18=Alexander B. |last19=Pedraza |first19=Fernando |last20=Pryke |first20=James S. |last21=Roque |first21=Fabio O. |last22=Settele |first22=Josef |last23=Simaika |first23=John P. |last24=Stork |first24=Nigel E. |last25=Suhling |first25=Frank |last26=Vorster |first26=Carlien |last27=Cardoso |first27=Pedro|hdl=2066/216853 |hdl-access=free }}</ref>

In a 2019 paper, scientists listed 100 studies and other references suggesting that insects can help meet the Sustainable Development Goals (SDG) adopted in 2015 by the {{wipe|United Nations}}. They argued that the global policy-making community should continue its transition from seeing insects as enemies, to the current view of insects as "providers of ecosystem services", and should advance to a view of insects as "solutions for SDGs" (such as using them as food and [[Biology:Biological pest control|biological pest control]]).<ref name="Dangles2019" /><ref>{{cite web |title=Sustainable Development Goals |url=https://sustainabledevelopment.un.org/?menu=1300 |publisher=Division for Sustainable Development Goals, United Nations}}</ref> The public in many countries is largely unaware of benefits and [[Biology:Ecosystem service|services]] that insects provide (such as honey, ecosystem balance, food for other animals, pollination, soil health, etc.), and negative perceptions of insects are widespread.<ref name="10.1073/pnas.2002547117" />

== Society and culture ==

=== In arts ===
In April 2019, in response to the studies about insect decline, Carol Ann Duffy released several poems, by herself and others, to mark the end of her tenure as Britain's poet laureate and to coincide with protests that month by the environmentalist movement [[Organization:Extinction Rebellion|Extinction Rebellion]]. The poets included Fiona Benson, Imtiaz Dharker, Matthew Hollis, Michael Longley, Daljit Nagra, Alice Oswald, and [[Biography:Denise Riley|Denise Riley]]. Duffy's contribution was "The Human Bee".<ref name="Duffy27April2019" />

=== Decline of professionals studying insects ===
One reason that studies into the decline are limited is that [[Biology:Entomology|entomology]] and [[Biology:Taxonomy|taxonomy]] are themselves in decline.<ref name=Yong2019/><ref name=Time/><ref name=Wired/> At the 2019 Entomology Congress, leading entomologist Jürgen Gross said that "We are ourselves an endangered species" while Wolfgang Wägele – an expert in [[Biology:Systematics|systematic zoology]] – said that "in the universities we have lost nearly all experts".<ref name=DW/> In 2016, Jürgen Deckert of Berlin Natural History Museum commented that while around 30,000 insect species are known to inhabit [[Place:Central Europe|Central Europe]], there are "only a few specialists" dedicated to the region, and even they often do monitoring as a side job.<ref name="SchwägerlYale2016"/> General biology courses in college give less attention to insects, and the number of biologists specialising in entomology is decreasing as specialities such as genetics expand.<ref name=Leather2007/><ref name=AE/><ref name=PS/> In addition, studies investigating the decline tend to be done by collecting insects and killing them in traps, which poses an [[Philosophy:Environmental ethics|ethical]] problem for conservationists.<ref name=RSB/><ref name=ICD/>

Further, the above describes the situation in the developed countries: the developing countries have typically not had time to build up their entomology in the first place. Consequently, nearly all of the major insect studies to date are from [[Earth:Europe|Europe]] and the {{wipe|United States}}, even though it's estimated that fewer than 20% of insect species worldwide are in those countries.<ref name="Wagner2021" />

==See also==
* [[Biology:Biodiversity loss|Biodiversity loss]]
* Colony collapse disorder
* [[Biology:Decline in amphibian populations|Decline in amphibian populations]]
* [[Earth:Holocene extinction|Holocene extinction]]
* [[Biology:List of endangered insects|List of endangered insects]]
* [[Biology:Pollinator decline|Pollinator decline]]
* [[Earth:Defaunation|Defaunation]]

== References ==
{{Reflist
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<ref name=AE>{{citation |first1=Kiran |last1=Gangwani |first2=Jennifer |last2=Landin |title=The Decline of Insect Representation in Biology Textbooks Over Time |journal=American Entomologist |volume=64 |number=4 |date=12 December 2018 |pages=252–257 |doi=10.1093/ae/tmy064 |postscript=.|doi-access=free }}</ref>
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<ref name=Barkham2019>{{citation |url=https://www.theguardian.com/environment/2019/apr/01/butterfly-numbers-fall-by-84-in-netherlands-over-130-years-study |title=Butterfly numbers fall by 84% in Netherlands over 130 years – study |newspaper=The Guardian |first=Patrick |last=Barkham |date=1 April 2019|postscript=.}}</ref><!--
<ref name=BBC>{{citation |url=https://www.bbc.co.uk/news/science-environment-47198576 |title=Global insect decline may see 'plague of pests' |publisher=BBC News |first1=Matt |last1=McGrath |date=11 February 2019|postscript=.}}</ref-->
<ref name=BBC04>{{cite web |url=http://news.bbc.co.uk/1/hi/sci/tech/3618332.stm |title=Scarce insects duck UK splat test |work=BBC News |first1=Alex |last1=Kirby |date=1 September 2004}}</ref>
<ref name=BMU>{{cite web |url=https://www.bmu.de/download/aktionsprogramm-insektenschutz/ |title=Aktionsprogramm Insektenschutz |date=10 October 2018 |publisher=Bundesministerium für Umwelt, Naturschutz und nukleare Sicherheit |language=de |access-date=4 March 2019 |archive-date=14 October 2018 |archive-url=https://web.archive.org/web/20181014164911/https://www.bmu.de/download/aktionsprogramm-insektenschutz/ |url-status=dead }}</ref>
<ref name=BorrellSA4Sept2012>{{citation |url=https://www.scientificamerican.com/article/one-fifth-of-invertebrate-species-at-risk-of-extinction/ |journal=Scientific American |title=One Fifth of Invertebrate Species at Risk of Extinction |first1=Brendan |last1=Borrell |date=4 September 2012}}</ref>
<ref name=Dangles2019>{{citation |journal=Ecosystem Services: Science, Policy and Practice |date=February 2019 |volume=35 |pages=109–115 |title=Ecosystem services provided by insects for achieving sustainable development goals |first1=Olivier |last1=Dangles |first2=Jérôme |last2=Casas  |doi=10.1016/j.ecoser.2018.12.002|s2cid=169994004 |postscript=.}}</ref>
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{{Insects in culture}}
{{insecticides}}
{{pesticides}}
{{Doomsday}}
{{Extinction}}

[[Category:Entomology]]
[[Category:Insect ecology]]

{{Sourceattribution|Decline in insect populations}}