File image: Professor Marcus Byrne.

“Small animals run the world.”

That’s how entomology Professor Marcus Byrne, of Wits University, describes the importance of the most abundant, and often overlooked, species on Earth: insects. 

"If you look at both ends of any ecosystem, the insects are utterly critical.” 

Last week, a landmark global review concluded that more than 40% of insect species could vanish within decades as researchers report dramatic rates of decline. 

The study, Worldwide Decline of the Entomofauna: A Review of its Drivers, found that a third of insect species are endangered, though it focused its research predominantly on declines in North America and Europe.

“The pace of modern insect extinctions surpasses that of vertebrates by a large margin It is evident that we are witnessing the largest extinction event on Earth since the late Permian and Cretaceous periods,” warned the authors in the study, published in the journal Biological Conservation. 

“Unless we change our ways of producing food, insects as a whole will go down the path of extinction in a few decades.”

Habitat loss and conversion to intensive agriculture and urbanisation are the chief culprits, followed by pollution mainly from synthetic pesticides and fertilisers, pathogens and introduced species. Climate change, too, is fuelling the insect crisis.

Byrne, who won the 2013 Ig Nobel Prize for Biology/Astronomy for discovering that dung beetles use the Milky Way galaxy for navigation, points to similar recent research from Germany reporting declines in flying insects and the huge drop in insect numbers in Puerto Rico. 

“The evidence is now mounting that the abundance of the small animals that run the planet is frighteningly declining and we need to worry To be honest, if we talk about South Africa, 90% percent of insects in this country don’t even have a name. We haven’t recorded our diversity yet, that’s how short we are of even cataloguing what we’ve got as it’s disappearing under our feet. Taxonomy is not seen as a sexy job and all the time we’re losing species.”

Climate change - changes in temperature and rainfall - will affect insect numbers dramatically, explains Byrne. "Insect metabolic rates are directly affected by environmental temperature, so as the temperature rises, it will increase the rate at which some insects develop, but might preclude some species from areas where they used to flourish because they simply become too hot."

Invasive alien species, too, particularly plants, "have been shown to reduce insect numbers and diversity in invaded areas, because they change the habitat composition".

The study’s authors call for the urgent rethinking of current agricultural practices, in particular a serious reduction in pesticide usage and its substitution with more sustainable, ecologically based practices, “to slow or reverse current trends, allow the recovery of declining insect populations and safeguard the vital ecosystem services they provide. Effective remediation technologies should be applied to clean polluted waters in both agricultural and urban environments”.

Professor Mark Robertson, of the department of zoology and entomology at the University of Pretoria, says the study is the most comprehensive review to date on insects. "It shows some alarming trends. The authors have found studies from around the world for most major groups of insects. 

"Why it matters it that it shows alarming declines in insects around the world. Insects are very abundant and play important roles in ecosystems. This includes things like pollination, pest control, decomposition and they are important food sources for other animals in ecosystems such as birds, reptiles and small mammals. It also shows that even for a group of organisms that is so abundant and diverse, humans are having a major impact."

Robertson says long term datasets on insect species are needed to show whether insect populations in SA and elsewhere on the continent have remained stable, increased or have declined.

"In the global review, there was only one dataset on insects included, work by Professor Michael Samways at Stellenbosch University on dragonflies."

Pesticide use and agricultural intensification are driving insect declines, "but other factors such as habitat transformation and climate change are also important. Unfortunately people do not appreciate the importance of insects in ecosystems or the important roles they play."