Sunday 25 February 2018

Australia's plummeting insect population

Insect population decline leaves Australian scientists scratching for solutions

24 February, 2018

A global crash in insect populations has found its way to Australia, with entomologists across the country reporting lower than average numbers of wild insects.

University of Sydney entomologist Dr Cameron Webb said researchers around the world widely acknowledge that insect populations are in decline, but are at a loss to determine the cause.

"On one hand it might be the widespread use of insecticides, on the other hand it might be urbanisation and the fact that we're eliminating some of the plants where it's really critical that these insects complete their development," Dr Webb said.

"Add in to the mix climate change and sea level rise and it's incredibly difficult to predict exactly what it is."

'It's left me dumbfounded'

Entomologist and owner of the Australian Insect Farm, near Innisfail in far north Queensland, Jack Hasenpusch is usually able to collect swarms of wild insects at this time of year.

"I've been wondering for the last few years why some of the insects have been dropping off and put it down to lack of rainfall," Mr Hasenpusch said.

Rain mothPHOTO: Jack Hasenpusch says he usually collects thousands of insects at this time of year, but this summer is particularly quiet. (ABC South East: Cassie Steeth)

"This year has really taken the cake with the lack of insects, it's left me dumbfounded, I can't figure out what's going on."

Mr Hasenpusch said entomologists he had spoken to from Sydney, Brisbane, Perth and even as far away as New Caledonia and Italy all had similar stories.
The Australian Butterfly Sanctuary in Kuranda, west of Cairns, has had difficulty breeding the far north's iconic Ulysses butterfly for more than two years.

"We've had [the problem] checked by scientists, the University of Queensland was involved, Biosecurity Queensland was involved but so far we haven't found anything unusual in the bodies [of caterpillars] that didn't survive," said breeding laboratory supervisor Tina Kupke.

Blue Ulysses butterfly on a leafPHOTO: There are concerns far north Queensland's iconic Ulysses butterfly species is also disappearing from the wild. (Supplied: Australian Butterfly Sanctuary)

"We've had some short successes but always failed in the second generation."
Ms Lupke said the problem was not confined to far north Queensland, or even Australia.

"Some of our pupae go overseas from some of our breeders here and they've all had the same problem," she said.

"And the Melbourne Zoo has been trying for quite a while with the same problems."

Limited lifecycle prefaces population plummet

Dr Webb, who primarily researches mosquitoes, said numbers were also in decline across New South Wales this year, which was indicative of the situation in other insect populations.

"We've had a really strange summer; it's been very dry, sometimes it's been brutally hot but sometimes it's been cooler than average," he said.

Cracked mud in a dry outback creek bed.PHOTO: Entomologist Dr Cameron Webb says dry conditions can affect the lifecycle of many insects, which in turn affects entire populations. (ABC: Nicola Gage)

"Mosquito populations, much like a lot of other insects, rely on the combination of water, humidity and temperature to complete their lifecycle.
"When you mix around any one of those three components you can really change the local population dynamics."
According to Dr Webb, when conditions are less than ideal the lifespan of mosquitoes and other insects plummets, thus reducing the sustainability of the entire population.

"If you're used to living for about three weeks when it's nice and warm and humid, and then you're only living for a week or so because it's really hot and dry then you don't have to chance to lay as many eggs, or do as much mating," he said.

"Those things have a knock on effect and it means the overall populations can often be much lower."

Important to listen to anecdotal evidence

At this stage, reports of insect population declines in Australia are only anecdotal.
And, without formal scientific research into the phenomena, Dr Webb said it was difficult to make accurate predictions or assessments about insect numbers.

A field researcher walks along an orchard row looking down at his clipboard.PHOTO: Dr Webb says corroborated anecdotal evidence from field researchers is often a sign that more formal research is required. (Supplied: Stuart Pettigrew)

On the other hand, he said, it is important to listen to the entomologists, ecologists and researchers who are in the field on a regular basis.
"You get a feel for what the general insect populations are like when you're doing a lot of field work," he said.
"I don't study cicadas, but I know what cicada numbers are like from year to year because I'm out and about in my local wetlands.

"When experts are relaying this kind of information it is something that we need to turn our mind to and think about what could be going on, and more importantly how do we work out if this is actually happening and what we do about it."

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