Australasian Science: Australia's authority on science since 1938

Is Australia Undergoing an Insect Armageddon?

Credit: Kevin/Adobe

Credit: Kevin/Adobe

By K. Tracy Reynolds & Ary Hoffmann

Long-term studies all over the world show a dramatic decline in insect diversity and numbers, but we know little about the health of Australian insect populations.

Insect species and other invertebrates have been quietly disappearing in many parts of the world for decades without fanfare. Being small and often viewed negatively, the decline or extinction of insect species has, apart from two or three cases, gone largely unnoticed and unreported in the wider community. Yet the loss of insects could have dramatic effects, from the loss of vital pollinators of the world’s food crops to the collapse of ecosystems.

But a shift is happening. Reports of dramatic declines in insect numbers have begun to be noticed.

Most recently, a review of the scientific literature received significant attention in the world’s media. Published in Biological Conservation (https://tinyurl.com/yxkhbbqc), Dr Francisco Sánchez-Bayoa of The University of Sydney and Dr Kris A. G. Wyckhuys of The University of Queensland examined studies documenting the loss of insect species across the globe. Based on these reports, they estimated that one-third of all insect species are under threat. This lends support to the suggestion that Earth is undergoing a sixth mass extinction event.

The importance of this review lies in its extensive examination of the literature. To begin with the authors identified a total of 653 papers dealing with insect declines. They then selected all those that documented quantitative changes in insect numbers over periods longer than 10 years. This is an important consideration: insect population numbers can vary markedly from year to year due to normal variations in the natural environment. Long-term studies are therefore required to show if an insect population is in decline. A good example is a recently published study of protected nature areas in Germany in PLoS ONE (https://tinyurl.com/y3c33rna), which estimated a 76% seasonal decline in flying insect biomass in several protected areas over a 27-year period.


Having documented declines, the next step is to determine the causes. Several factors were identified by Sánchez-Bayoa and Wyckhuys. Of these, agricultural intensification was the driver in the greatest number of cases. Agricultural intensification brings with it numerous changes in farming practices. Beginning in the 1950s and coined the “Green Revolution”, agricultural intensification greatly increased the productivity of farmland via the introduction of mechanisation, pesticides, herbicides and chemical fertilisers.

This resulted in significant changes to the farm landscape. Habitats such as hedgerows and natural drainage systems were removed, and agricultural regions shifted from a patchwork of smaller fields growing different crops to large fields of monocultures. The more effective removal of weeds via herbicides also further reduced plant diversity. The result has been a change from biodiverse communities of insects, many with specialist food and habitat requirements, to communities consisting of a small number of mostly generalist species.

The impacts of habitat removal and insecticides are predictable and easily understood. However, sometimes the impacts are not immediately obvious. For example, a 2008 paper published in the Annual Review of Entomology (https://tinyurl.com/y2jr3hdw), found that the introduction of chemical fertilisers has caused the decline of three species of bumblebees in Britain. Why should this be the case?

In the past, farms had practised crop rotation. Clover and legumes, upon which these species forage for nectar, were planted to achieve an increase in soil nitrogen content. However, this practice ceased when chemical fertilisers, which provide much quicker and easier ways to increase soil fertility, were introduced. Hence the foraging plants for these three bumblebee species was greatly reduced, resulting in their decline.


So what is happing in Australia? The publicity surrounding the Sánchez-Bayoa and Wyckhuys paper led to nostalgic discussions of the disappearance of insects that people recalled from childhood. A common story was that people noticed a reduction in the number insects on car windscreens after long drives in the country. Many people recall having to frequently clean car windscreens, whereas this is now no longer the case. Another common story was the loss of Christmas beetles, groups of shiny and colourful beetle species that used to appear in summer but are now reported rarely.

So is there major decline in insects in Australia? The worrying answer is that we don’t actually know. A surprising fact that was highlighted by Sánchez-Bayoa and Wyckhuys was the almost total absence of long-term studies in Australia. At this point, although it is strongly suspected that there has been a decline, we have little concrete data to support the anecdotal reports. Anecdotes can be very useful in suggesting the existence of a possible phenomenon, but they are pointers rather than representing rigorous scientific evidence. It could be the case, for example, that the reduction of insect strikes on windscreens reflects changes in the design of cars, which are now more aerodynamic than in the past, or perhaps the removal of roadside vegetation that formerly supported a higher abundance of insects.

Given the importance of insects in natural and urban environments, it is a matter of urgency that we establish the situation in Australia. Insects and other arthropods form vital links in food chains, as well as performing ecological services in ecosystems. These services include the pollination of plants, including food crops, and the decomposition of organic matter.

We have certainly experienced many of the factors that are thought to have reduced insect numbers around the globe, including habitat removal, agricultural intensification, the expansion of cities into what was once farmland, the increased use of a diversity of insecticides, and invasions by exotic species. We are also likely to be strongly affected by the effects of global climate change, which the review identified as the fourth main driver of insect declines. Increases in average as well as extreme temperatures, and changes to drought frequency and intensity, are likely to have major impacts on insects in ecosystems here.


One case recently highlighted is the lack of Bogong moths in two caves in the Snowy Mountains over a 2-year period. The cause is suspected to be a lack of vegetation for the caterpillars, resulting from drought conditions in their breeding grounds. Other caves still contained moths, and the suggestion is that they may come from breeding grounds not affected by drought. These moths are a crucial food source for the mountain pygmy possum, without which possums cannot maintain good condition while they hibernate over winter. Dr Dean Heinze of La Trobe University, who is involved with researching this endangered species, told The Guardian that many possums are currently underweight, with dead young being found in the pouches of females.

Like the mountain pygmy possum, many small marsupials in Australia depend on insects as a food source. Evidence of the effect of insect loss on vertebrates has also been documented in other parts of the world. In Puerto Rico, a decline in insect biomass reported in the Proceedings of the National Academy of Sciences (https://tinyurl.com/y26gc8r2) in 2018 was accompanied by a parallel drop in the numbers of birds, frogs and lizards. In the UK, a paper published in Conservation Biology in 2004 (https://tinyurl.com/yxn3b2cu) reported that a reduction in insect biomass due to pesticide use resulted in a decline in bat species in some areas.

Australia does, however, have an excellent resource to begin investigating this phenomenon. Although recent data are lacking, we have a rich store of historical information on the distribution of species from the past. Beginning in 1929, expeditions to find insects were mounted all over the country, including in remote regions, with the aim of surveying and documenting the nation’s insect fauna. These collections and donations from private collectors now form the Australian National Insect Collection in Canberra.

One example of the use of historical collections is a 1990 study in the Proceedings of the Ecological Society of Australia that examined the changing distribution of the trapdoor spider species Idiosoma sigillatum in Western Australia following land clearing and urbanisation. Perhaps it is time to mount new expeditions to see if there have been similar changes in the distribution of other species. Insects collected and recorded by amateur and professional entomologists could provide useful information on the issue. With such information, we can help predict the likely insect losers (and winners) in our increasingly variable climate, and with this knowledge develop strategies to mitigate the potential consequences.


K. Tracy Reynolds is a biology teacher at Viewbank College in Melbourne. Ary Hoffmann is a professor and biologist at the Bio21 Institute of The University of Melbourne.