The extent of the much-reported "insect apocalypse" has been called into question by a new wide-ranging analysis of insect population studies from across the globe.

Key points: Average decline is closer to 9 per cent, with freshwater insects increasing

Average decline is closer to 9 per cent, with freshwater insects increasing But 9 per cent decline is still concerning and could have severe consequences economically and environmentally if the trend continues

But 9 per cent decline is still concerning and could have severe consequences economically and environmentally if the trend continues Accurate long-term data is needed to focus conservation efforts

Previous estimates have put average global insect declines at as much as 25 per cent per decade, stoking fears that we are on the precipice of a mass insect-extinction event that could have huge ripple effects throughout the world's ecosystems.

But new research, published in the journal Science today, has found the average rate of decline is more like 9 per cent, and some freshwater populations are actually increasing at an average rate of 11 per cent per decade globally.

The meta-analysis of more than 160 long-term insect population studies across 41 countries, found there is a high range of variability in terrestrial insect population trends depending on location.

While North America and parts of Europe had the biggest population losses, some sites in western Europe and Asia showed an overall increase in insect numbers.

There was not enough data from Australia to establish a trend.

Lead author Roel van Klink from Leipzig University in Germany said he was not surprised to find the rate of insect loss wasn't as dramatic as we'd feared.

"We were aware of the existence of many datasets that had not made it into the discussion about insect declines," Dr van Klink said.

"We had hypothesised that the reason why they were not published was that they showed no declines — we call this publication bias."

Publication bias can happen when a study achieves "no result" or doesn't find any trends of interest.

Journals may not rush to publish a study that finds, for instance, that there are the same number of insects in place A in 2020 as there were in 1970.

On the flip side, a study that finds a total collapse of insect numbers at place B in the same period is likely to get a lot of interest.

What we end up with in the published literature is only the studies showing dramatic results.

Disappearing insects has 'dangerous consequences' despite 'alarmist papers'

Insect numbers increased on average across cropping areas of North America, with researchers suggesting some agricultural practices have improved. ( Getty Images: Michael Xiao )

David Merritt, an entomologist at the University of Queensland who wasn't involved in this study, was also not very surprised by these latest findings.

"I am aware of some of the, what you might call 'alarmist' papers [on insect decline]," Dr Merritt said.

"It's spoken about in the insect world, but people are hesitant to be seen to be playing down what is still a serious issue."

While a reduced rate of insect decline is good news, the researchers behind the latest study hastened to stress that 9 per cent per decade was still very high and that there were likely to be severe consequences if the trend wasn't reversed.

"This [still] amounts to about a quarter [of the population] in 30 years, and because this is an average, it also means there are places that are doing much worse than this," Dr van Klink said.

"If insects are disappearing this has dangerous consequences for our food security, because all our fruits are pollinated by insects.

"We believe this is something to be taken seriously, but it's not yet too late to do something about it."

Factors that can lead to insect decline

Research has linked the widespread use of some pesticides, in particular neonicotinoids, to global declines in insect numbers, but Dr Merritt said there were other significant factors at play.

"Habitat loss is the big one — a reduction in the diversity of different grasslands and other ecosystems," he said.

"When you throw in climate change on top of that you can almost throw your hands up in the air because climate change is something that's happening really fast."

While the latest study found a correlation between increasing urbanisation and insect loss, the researchers were surprised to see a trend of increasing average insect numbers over cropping land in North America since the 1990s.

They hypothesised that improved farming methods and more targeted use of insecticides may have taken the pressure off insect populations that had been decimated by intensive agriculture in the previous decades.

Improvements in insect abundance in parts of Asia also coincided with the fall of the Soviet Union, and the demise of some of the polluting Soviet-era industries.

Likewise, improved management of catchment areas may have contributed to greater water quality and by extension, increasing freshwater insect numbers, they suggested.

But, while the trend in freshwater insect populations was encouraging, freshwater ecosystems cover only 2.4 per cent of the Earth's landmass and therefore don't counterbalance the terrestrial insect decline.

'It's not your imagination', there are a lot of insects right now

Some insects have boomed in eastern Australia following fresh rains. ( ABC Science: Nick Kilvert )

Dr Merritt said there has been a noticeable decline in insect numbers during the drought that has gripped eastern Australia for the last few years.

"Some guy rang up [talk-back radio] saying he drove from Alice Springs to Adelaide and didn't get any splats on his windscreen," he said.

"There was this real alarmist 'where have all the insects gone?' feeling."

But since rains in summer this year, many places are now experiencing a boom of things like butterflies, moths and even flies.

"It's not your imagination. I've noticed it, people working at the museum have definitely noticed it, because they're getting contacted by the public [about the insects]," he said.

"We've had a longish period of drought and then we got that heavy rain in I think it was February …it's just like nature kicking back into gear."

To get accurate long-term population trends that iron out those natural fluctuations, Dr Merritt said you need studies to span decades.

Which is why meta-analyses like the latest research were valuable.

While insect declines are certainly of very serious concern, Dr van Klink said we need research to be accurate in order to best target efforts to reverse those trends.

"Our data shows that the trend is extremely variable across the world, and some places need urgent action whereas others don't."

"We really believe this nuance is needed in this debate, and in the actions we take. Otherwise we'll be wasting the little money that we have available for insect conservation on ineffective actions."