Cape Zebra Cockroach from Table Mountain National Park in the Western Cape.
Despite fears over “insectageddon”, there is a lack of data about virtually all insect species globally and there is virtually no data on species in Africa.
This is according to a team of scientists from South Africa and the UK, who have developed a synthesis framework, integrating multiple evidence streams, which will allow for the rapid assessment of changes in insect biodiversity.
“We know that insect biodiversity is changing, and that there have been many declines in parts of the world,” they wrote in a major review article published in the journal Science, recently. “However, we do not know how severe or pervasive the problem is. More critically, we lack a clear understanding of why insect biodiversity is changing.”
Insects are an extraordinarily diverse and abundant group of creatures and are essential to terrestrial and freshwater ecosystem functioning, which in turn is critical to human well-being, the authors wrote in their study.
“Most of the world’s flowering plant species depend on animal pollinators to reproduce, with an estimated 82% of species pollinated exclusively by insects … Insects compose the bulk of food sources for many birds, bats, reptiles, freshwater fishes and other vertebrates.”
There is “overwhelming” evidence of changes in insect communities in recent decades, the researchers said. “These changes include rapid local and regional declines in abundance, occupancy, biomass and diversity as well as the reorganisation of communities.”
Concern over these changes has permeated across scientific, public and policy sectors. And although some narratives have “likely exaggerated” the extent of insect declines, insects are clearly threatened by a combination of widespread human-caused drivers, including land-use change, climate change, agricultural intensification, pollution and introduced species.
Insects are a challenging group to study because they are hyperdiverse, have complex life cycles, are functionally complex and experience substantial population fluctuations.
“In addition, the fragmented and unrepresentative available evidence base means that the global state of insect biodiversity remains unclear. In the face of these challenges, new approaches are required to determine the global status of insects and their responses to drivers of change,” the authors wrote.
There is an urgent need to understand how, and crucially why, insect biodiversity is changing. “This will facilitate more robust assessments of insect biodiversity change and improve our confidence in those assessments so that informed conservation and policy recommendations can be made to protect insect biodiversity.”
The aim of the synthesis framework is to provide a roadmap for an evidence-based synthesis of changes in insect biodiversity on which conservation policies can be built, said Cang Hui, a biomathematician from Stellenbosch University’s department of mathematical sciences and one of the co-authors.
“We cannot wait decades for comprehensive monitoring data,” Hui said. “The Kunming-Montreal Global Biodiversity Framework set an ambitious goal to restore biodiversity by 2050 — to achieve this we need to understand what scale of actions will be required to reverse historical declines.”
Hui is part of a team of scientists working on the Global Insect Threat-Response Synthesis (GLiTRS) project. It is funded by the National Environmental Research Council Highlight Topics programme, a consortium of six institutions in the UK and South Africa.
Their objective is to build a global threat-response model, integrating many lines of existing evidence.
“We argue that the urgency of the situation demands that we make better use of the data that is available now, however limited,” the authors noted in their review paper.
Four lines of evidence are synthesised and integrated in the GLiTRS project to address this challenge — time series, spatial comparisons, experiments and expert opinion. Mathematical ecology and modelling help identify trends from the first two sources.
“Insect time series exhibit intermittent fluctuations, yet they are both temporally auto-correlated and spatially synchronised,” said Hui. “If we can determine the correct spatial and temporal scales, we may be able to extrapolate these trends to unsampled areas and future time periods.”
Rob Cooke, an ecological modeller at the United Kingdom Centre for Ecology and Hydrology, and joint lead author of the study, agreed. “We need to find out whether insect declines are widespread and what’s causing them. The challenge is like a giant jigsaw puzzle where there are thousands of missing pieces but we do not have decades to wait to fill these gaps and then act.”
According to the review, despite the growing recognition of the ecological and economic importance of insects, research on insect biodiversity has been limited and underfunded.
“As a result, the available evidence describing insect trends is spatially, temporally and taxonomically unrepresentative, so that the overall magnitude of the problem remains unclear,” the scientists said.
Current evidence, they said, is biased toward human-dominated landscapes in Europe and North America. “Taxonomic bias favours easily observed or identified groups, such as butterflies, bees and dragonflies, whereas more taxonomically intractable or geographically isolated groups (such as parasitoid wasps, earwigs or icebugs) have been neglected.”
They noted how Goal A of the Kunming-Montreal Global Biodiversity Framework refers to metrics such as population abundance and extinction risk, for which there is excellent data for vertebrates.
By contrast, a mere 1.2% of insect species — 12 100 species out of 1 million described species — have undergone the International Union for Conservation of Nature Red List assessments necessary to calculate extinction risk.
About a quarter (3 107 species) were evaluated as data deficient. “An even smaller fraction has been assessed more than once, undermining any ability to understand changes in extinction risk.”
These shortfalls underline the need for new approaches to deliver a more comprehensive,
globally representative picture of the state of insects to inform scientific research, public understanding and biodiversity policies, the authors argued.
“Because of the sheer number of insects, their vast ecological diversity, and the paucity
of available data, the challenge of understanding global insect biodiversity change is an immense task.
“To date, limited resources have been directed toward this task … Only through harnessing the full breadth of available evidence can we piece together the fragmentary data into a coherent picture. It is a small, but important, first step toward an insect-positive future.”