How can we stop Insect Armageddon?

CHRIS HATZIS

Eavesdrop on Experts – stories of inspiration and insights. It’s where expert types obsess, confess and profess. I’m Chris Hatzis, let’s eavesdrop on experts changing the world – one lecture, one experiment, one interview at a time.

Declining insect population sizes are causing grave concern around the world as insects play essential roles in food production and ecosystems. Environmental contamination by intense insecticide usage is consistently proposed as a significant contributor, among other threats.

Phil Batterham is Professor Emeritus at the School of BioSciences and the Bio21 Institute, University of Melbourne. His research looks at the interaction of chemical insecticides with pest and beneficial insects. Understanding this interaction will underpin the development of more effective and sustainable control strategies, with a reduced environmental impact. Agricultural productivity and ecosystem health are both absolutely dependent on insects.

Phil Batterham sat down for a Zoom chat with Dr Andi Horvath.



ANDI HORVATH

Phil, if I was your taxi driver and I asked you, what do you do, what would you say?

PHIL BATTERHAM

Good question. I’d say that I work on insecticides and what they do to insect pests but also to beneficial organisms that we rely on, such as honeybees.



ANDI HORVATH


So, are we trying to eradicate a lot of insects in farms all around the world?

PHIL BATTERHAM

No, that number is pretty small actually. It’s estimated that there are about 5.5 million insect species on Earth and those that are pests may number in hundreds – nowhere near the millions – so it’s a minority of insects that cause damage in agriculture and in fact many insects are beneficial and really vital to us and to ecosystems.

ANDI HORVATH

So Phil what’s the relationship then between controlling pests, insecticides and the ecology?

PHIL BATTERHAM

Okay, well the first step is that insecticides, many of them target the nervous system of insect pests. So, around your house you might use an insecticide – Mortein – and if you spray a fly with Mortein it dies quite rapidly because it binds to a target protein in the brain of the fly and it’s a very rapid response. For that reason, many insecticides are targeted to proteins in insect brains and these insecticides are not particularly pest specific, in fact, they’re not really pest specific at all. In other words, they bind to proteins that are found not only in the brains of pests but also in the brains of non-pest insects.

ANDI HORVATH

Have humans altered insect populations around the world?

PHIL BATTERHAM

Well, clearly, we do in a number of ways, so that will be via the use of insecticides, but it can also just be due to all sorts of agricultural practices that we employ beyond insecticides. It can be due to the clearing of forests; it can be due to pollution. So, there are many ways in which we are impacting insects and clearly global climate change is really high up on that list because insects are unable to modulate their body temperature. Humans are able to control their body temperature – it sits normally around 37 degrees – for insects their body temperature is the temperature that is around them, the ambient temperature.

They have a certain range of temperatures over which they are able to survive and reproduce and if temperatures get outside of that range, then they will not be able to survive and reproduce. So, we are impacting insects in many ways by things that we do quite actively and the things that we are doing maybe actively and passively in terms of just allowing the climate change issue to get worse.

ANDI HORVATH

Phil, I’ve heard you use the term ‘Insect Armageddon’. Is that what you’re referring to?

PHIL BATTERHAM

It’s not a term of my making but there are now many published studies that are showing that insect populations – particularly land-based insects, terrestrial insects – those populations are shrinking at a really worrying rate. So, one study said that the decline had been 10 per cent per decade since 1925 and more recent studies are saying one to two per cent per year would be the average decrease for land-based insects.

ANDI HORVATH

Is there a tipping point that’s estimated for insect populations to collapse that really are irreversible?

PHIL BATTERHAM

There is a tipping point, and it will be species-specific, so there’s not going to be a general rule, but I think one thing that’s really important to note is that it won’t be just a matter of the insect populations dying out, but there’s recent research that suggests that maybe the first thing that we would see – particularly considering climate change – are reduced rates of fertility, and Ary Hoffmann at Melbourne University has been involved in this research. It turns out that male fertility drops in insects at temperatures that are several degrees cooler than temperatures required to kill. So, you may see populations gradually shrinking with elevated temperatures because of this impact on fertility way before you would see death via increased temperature, so that’s a really important point.

On the other side of the coin, organisms that are dependent upon insects in their food chain will be progressively impacted as insect population sizes shrink. So, there is research that birds, for example, that depend upon insects for their food, their populations are shrinking in a way that’s correlated with decreases in insect population size.

ANDI HORVATH

This is quite critical for the planet. Are there plans in place to cater for this possibility?

PHIL BATTERHAM

Well, I have to respond firstly to your observation. Yes, it’s significant for the planet and often we don’t give much thought to this, but insects are really critical elements in ecosystems. So, I’ve given the example of birds. Insects are a very important part of the food chain and so you remove that food resource, or it becomes more limiting, and you have an impact on organisms that we seem to care more about.

ANDI HORVATH

You mentioned honeybees earlier. What’s the status of honeybees globally?

PHIL BATTERHAM

Well, honeybees – species Apis mellifera – is used widely around the world and it is used to produce honey, but those honeybees do provide pollination services. Our agriculture is dependent upon pollination services from a very wide range of pollinator species, some of them wild bees and there are other insects that also pollinate. Without those pollination services, we would be in dire straits producing food. There’s a site on the web called Two World Clocks and you can see there two clocks, one shows increasing human population size – it’s going up rapidly – and the other clock shows the amount of arable land – the land available and suitable for agriculture – and that’s going down quite quickly, so the amount of food per hectare that we need to produce is effectively going up by the minute.

At the moment if we shared food equally around the world there would be more than enough but there may come a time in the future where that is not true, so we cannot afford to lose the pollination services of these insects. Unfortunately, at the moment, we can’t afford to lose insecticides either, as a control agent, because agricultural productivity is heavily dependent upon the use of insecticides. So, it concerns me that insecticides are important for food production, but they may be having impacts on pollinators which are also essential for food production.

ANDI HORVATH

This is very important stuff. What has been one of your projects that you’ve really enjoyed doing research about?

PHIL BATTERHAM

I had a PhD student who examined low-dose impacts of insecticides on a model organism called Drosophila. So, it’s not a honeybee, but as I said before, the targets of these insecticides are highly conserved between Drosophila – the vinegar fly – and the honeybee, Apis Mellifera. So, the things that we saw in Drosophila really are most likely to apply to the honeybee. The student – his name is Felipe Martelli – he’s graduated and he’s now working at Monash University as a postdoctoral research fellow, but he worked on two classes of insecticides and they both did pretty similar things. One of them is a neonicotinoid insecticide called imidacloprid.

Its use in agricultural settings has been banned in Europe because of demonstrated impacts on the honeybee and the other was an organic insecticide called spinosad. Now, both of these insecticides Felipe was able to show cause an elevation in chemicals that we call reactive oxygen species. These chemicals have the capacity to damage other molecules inside an organism. They damage DNA, they damage proteins, they damage lipids or fats, and they are highly toxic. Felipe was able to show that these insecticides were damaging mitochondria, which are the energy centres in cells. There was a precipitous drop in levels of energy, mitochondria were being damaged, and this happened quite quickly in short term exposures. In longer chronic exposures in adults, he saw neurodegeneration and blindness.

So, this was clearly very concerning because it extends the observation that people have been making. Of course, people have observed that these insecticides impact the behaviour of honeybees, that’s natural because they function in the nervous system. The targets of these insecticides are there in the nervous system and the insecticides interact with them, perturbing behaviour. But Felipe showed mass perturbations of metabolism which would have a range of other impacts upon survival in natural environments. He also showed impacts on immunity, and this is really important in terms of honeybees because while the compound that Felipe worked on – imidacloprid – is so often blamed for the demise of honeybee populations, particularly in Europe, it does not do that alone because we’re not seeing major impacts on honeybee colonies in Australia, but they do in Europe.

The big difference is that in Europe they have this mite which is parasitic called the Varroa mite and both the mite itself and the viruses it carries have an impact on honeybee colonies. So, we think that clearly the neonicotinoid insecticide – imidacloprid – is maybe not the major cause but we think it predisposes – it makes bees more susceptible – to this Varroa mite and the viruses that it carries. So, this research, it concerned me a lot.



ANDI HORVATH

Yeah, it’s pretty important. I can imagine it – if you’re predisposing bees and weakening their system so they get the Varroa mite, I mean that could lead to colony collapse much easily.

PHIL BATTERHAM

Yes. But those other effects that Felipe saw – energy loss – there are a range of functions that are really energy-dependent. Let me give you three. Bees are really dependent upon behaviours that allow them to locate sources of pollen and nectar and that requires both brain activity and in the going and returning it also requires energy. The brain consumes a disproportionate amount of the energy that an insect produces and clearly flight requires energy and reproduction requires energy and so we’re very concerned about the downstream impacts that we see following low dose insecticide exposures.

ANDI HORVATH

What are some of the surprises that you’ve encountered in your research projects or turning points that you might have…?

PHIL BATTERHAM


Well this was a major turning point for us. I’ve spent most of my career looking at what insecticides do to pests and in fact the most important work I’ve done, particularly with Trent Perry – working in my lab – and Trent has been very active in using Drosophila to identify the targets of insecticides, so that’s been a major focus for decades for my lab. But we’ve really – this work of Felipe’s has turned around what we do, and my major focus now is on these low dose impacts because we have good reason to believe that most chemical insecticides will cause the sort of damage that Felipe has seen with imidacloprid and spinosad. I have to say that although spinosad is labelled as organic, it creates more damage at much lower doses than imidacloprid does.

So, I’m really concerned generally about insecticides and these downstream impacts that they will have in non-pest insects, and I think it’s really important for us to get on and study other insecticides and verify that they are causing such damage or clear them of it. Because, as I said, at the moment we need to use insecticides in agriculture and as a bare minimum we need to be using the safest ones.

ANDI HORVATH

What got the whole ball rolling for you in getting into the world of insects and genetics?

PHIL BATTERHAM

Genetics [laughs] – it’s kind of an interesting story. I was an undergraduate student at La Trobe, I wanted to be a schoolteacher and in those days La Trobe University had a 4-3-2 system. So, you took four subjects in first year, three in second year and two in third year. I wanted a broad-based scientific education so that I could teach a number of different subjects in high school and so in first year I took a couple of biology subjects that included some genetics, and I took chemistry and maths. I dropped maths in second year, and I took chemistry, botany and genetics and at the end of second year I was really keen to drop chemistry and so in third year I did botany and genetics.

I loved both but botany tended to be taught like everything was known where genetics, it was taught like nothing much was known, and it was all there to discover and that excited me. So, I did honours in genetics, and I worked with a man who went on to be a deputy vice-chancellor of Melbourne University – John McKenzie – and I was his first student. I worked on actually an enzyme called alcohol dehydrogenase and I was working on a toxin – clearly ethanol – and that was in Drosophila. In my PhD I also worked on toxins, and I was looking at phenols, and then I went off to the United States and I worked more on alcohol, came back to Australia and I was working on heavy metals and then began to renew my working relationship with John McKenzie and began to work on insecticides.

Initially, I was interested in them as a model of evolution because in pests insecticides caused – well the exposure to insecticides ultimately leads to the evolution of insecticide resistance. It’s a kind of evolution that you can study in the field – so it had a lot going for it – but the further I went the more I became interested in the applied dimension of the work.

ANDI HORVATH

Where are we with insecticide resistance?

PHIL BATTERHAM


It was almost guaranteed to happen. So, if you use an insecticide, you will be applying it to pests at doses that will kill them. So, if a mutation arises in a single insect that will allow them to survive a dose of insecticide, then that particular mutation is going to increase in frequency because that organism is going to reproduce whereas those that are susceptible will not reproduce. So, that mutation will increase in frequency, and it can happen really quite quickly. So, there was a case in Australian agricultural history, there was an insecticide called dieldrin which was used to control the Australian sheep blowfly and within two years of that chemical being introduced, there was high-level resistance from one end of this country to the other.



ANDI HORVATH

Next time we stop and smell the roses and we notice an insect crawling on it, what would you like us to think about?



PHIL BATTERHAM


I’d like us to think about the interconnectedness of life on this planet. Now, there’s two dimensions to that. Firstly, that the welfare of all of the organisms on this planet that are not human is interdependent upon other organisms. I’d like them to think about a game of Jenga that if you pull out a block it may not make the tower fall but if you pull out the wrong block or too many blocks then the tower collapses and ecosystems are like that. The second thought I’d like people to have is our interdependence. We are a lifeform here and we are interdependent on other lifeforms. Humans are very self-centred so we rejoice with advances in medicine that may keep us alive because we have concerns about disease – and at this moment particularly infectious disease – but in reality, our health and wellbeing is dependent upon so much of the biodiversity that is around us.

So, research on insects becomes really important if we’re talking about ecosystems collapsing, about beneficial species such as pollinators disappearing. This is every bit as important to us as the latest medical advances and so we do need to think about the environment. Climate change is the biggest issue on planet Earth now and going forward, we need to be aware of that. COVID-19 is really rocking our foundations but it will pass but the damage that we are doing to the environment with greenhouse gas emissions, with land clearing, with all sorts of other things that we are doing, present long-term danger and we need to focus on that, not in a morbid way, but by taking every opportunity to find the solutions that are being offered to us by science that’s already been done.


ANDI HORVATH


Professor Phil Batterham, thank you.

PHIL BATTERHAM

Thank you.


CHRIS HATZIS

Thank you to Phil Batterham, Professor Emeritus at the School of BioSciences and the Bio21 Institute, University of Melbourne. And thanks to Dr Andi Horvath.

Eavesdrop on Experts – stories of inspiration and insights – was made possible by the University of Melbourne. This episode was recorded on June 15, 2021. You’ll find a full transcript on the Pursuit website. Production, audio engineering and editing by me, Chris Hatzis. Co-production – Silvi Vann-Wall and Dr Andi Horvath. Eavesdrop on Experts is licensed under Creative Commons, Copyright 2021, The University of Melbourne. If you enjoyed this episode, review us on Apple Podcasts and check out the rest of the Eavesdrop episodes in our archive. I’m Chris Hatzis. Join us again next time for another Eavesdrop on Experts.