3 takeaway lessons from the PNAS Special Feature on “The Global Decline of Insects in the Anthropocene”

“Nature is under siege,” declares the introductory article of the PNAS Special Feature on “The Global Decline of Insects in the Anthropocene.” In an era of elevated atmospheric CO2 levels, intense industrial agriculture, and increasing urbanization, it is no surprise that according to a 2019 United Nations report, around 1 million plant and animal species are now threatened with extinction. Half of those threatened are insects.

The PNAS Special Feature offers a collection of 12 original articles including original research, literature reviews, and perspective pieces by entomologists on the alarming phenomenon of global insect decline. The collection is rich with information, but here are my three main takeaways from the special feature:

1. Insect populations are in decline. This decline, however, is complicated and multifaceted.

To say that insect populations-at least in some species-are in decline is a rather uncontroversial statement in the entomological world. While there is much variation concerning geography, time, and taxa, reports from several studies estimate that insect abundance is declining at a rate of 1–2% per year. In 2020, scientists even issued a ‘warning to humanity’ on the insect extinction crisis.

Image by Michael Anfang from Unsplash

The drivers of insect extinction, however, are many and vary across regions and species. The Anthropocene is unleashing upon insects “death by a thousand cuts” through pollution, pesticides, deforestation, habitat fragmentation, agricultural intensification, invasive species, climate change, and a whole host of human-associated inputs. How and to what extent these drivers interact with each other remains to be deciphered by science, but it is clear that no one input is the single cause for global insect declines and thus there will be no silver-bullet solution to our current crisis.

2. The ‘insect apocalypse” is not upon us, rather, there will be winners and losers in the Anthropocene if we keep with our current course.

Highly publicized studies, such as a 2017 German study which found an over 75% decline in flying insect biomass over 27 years, were initially reported in a manner that painted the picture of an imminent insect apocalypse. The story of global insect decline, however, is a bit more complicated.

Insect declines in both numbers and diversity vary geographically and taxonomically. For example, analyses of hoverfly species data from German reserves reveal stronger declines in more common species than rarer species over 15 years. Researchers also found that declines in hoverfly biomass (i.e., the total weight of all hoverflies in an area) predicted declines in overall hoverfly diversity.

Moreover, the drivers of certain insect declines are still being identified. For example, arthropod declines in the Luquillo Experimental Forest in Puerto Rico initially attributed to climate change were later revealed to be in response to periodic disturbances such as hurricanes.

Image by Wynand Uys from Unsplash

It is also important to note that not all insects are in decline; some insect populations are increasing. Freshwater insects, for example, are increasing by 11% per decade since 1925, likely due to clean water legislation in the latter half of the 20th century. Moreover, insects with close human associations such as cockroaches and honeybees are likely to persist well into the Anthropocene.

None of this, however, is to downplay the threats facing insects in the coming decades. While there will be winners in the Anthropocene, losing the “losers” take a catastrophic toll on even the few “winners”-humans included.

3. Cataloging and documenting insect species before they vanish will be crucial in the coming decades.

Insects are the most diverse group of organisms on the planet and yet the full extent of their vast biodiversity remains understudied. To date, taxonomists have described over one million insect species, yet an estimated 4.5 to 7 million remain to be discovered, most of which are believed to reside in the tropics.

The study of entomology has historically focused on a few, economically important, or charismatic species of interest. Consequently, we lack historical data on many groups which makes it all the more difficult to ascertain the nuances of decline for certain taxa when we lack a historical baseline to compare present-day losses to.

Natural history records from historically wealthy countries in the Global North have created an additional geographic bias that neglects that majority of biodiversity which resides in the Global South. Moreover, these regions tend to lack the resources required to carry out such extensive cataloging projects. Species identification, especially of smaller, microfauna, often requires extensive microscopy, dissection, and DNA analyses, introducing work and costs not required when dealing with vertebrates.

Critically, these understudied tropical regions are the places that are currently experiencing the highest rates of habitat loss and fragmentation, and it will ultimately become a race to catalog these creatures before they are driven to extinction.

Image by Markus Spiske from Unsplash

However, there are promising technological advances that may aid in this endeavor. Remote camera monitoring, bioacoustics, environmental or eDNA, and digitized natural history collections, paired with deep learning computer artificial intelligence may allow us to expedite the rate at which we can catalog these creatures before the window of opportunity is forever closed.

The next few decades will be crucial for insects. Avoiding catastrophic climate change, reforming our agricultural systems, and re-centering biotic communities in all our future decision-making are necessary steps we-particularly in the Global North-will need to take if we are to preserve the integrity of insect systems. We all have a lot of work to do but it can start simply at home. As Kawahara and others write, individuals can take simple actions such as growing native plants, reducing pesticide use, and limiting exterior lighting at night.

An advantage insects have in this fight is that they are rather resilient can bounce back from disaster rather quickly. All we need to do is change and they will do the rest.

Originally published at https://www.notazookeeper.com on January 14, 2021.

Entomology Master's student | Science Writer & Fiction Author | Writes about animals, nature, & the people who study them