Why are the numbers of insects in fast decline? What does it mean for our food supply and our long term survival? Scientists say climate change is not the only reason. Maria Armoudian speaks with Andrew Dopheide about the current plight of our insect population.
Andrew Dopheide is a Researcher at Landcare Research and has a Ph.D. in Biological Sciences from the University of Auckland.
This interview has been edited for clarity and length
Maria Armoudian: Perhaps it is important to start with why it is important to understand what is happening with our insects?
Andrew Dopheide: Well, insects are the most diverse group of organisms on the planet. There are millions of species of insects basically and invertebrates collectively are the majority of animals on Earth. So they are a really huge group and we don’t really understand much about most of them just because of the sheer number of species there are. But it is known that they have important roles in ecosystems such as nutrient recycling and decomposition, pollination – bees are an obvious example of this they are very important for pollination for something like eighty percent of the world’s crops – also the direct inputs of nutrients into the soil, shredding and decomposing stuff in the soil so it makes the nutrients available to other things. Also food web effects such as insect and invertebrate predators who have been found to have effects on things such as carbon cycling and nutrient mineralisation. There are a small range of insects that we know quite a lot about in terms of their role in ecosystems but there are also a vast array of other invertebrates and insects that we really don’t know anything about, but it is fair to assume they have a very important role in the ecosystem.
MA: So we are hearing a lot about the decline of certain kinds of insects, the bees for example, but I understand it is beyond the bees at this point. What is in decline and how much is it in decline?
AD: There have been a few studies looking at particular insects, such as certain butterflies, for example which have shown they have declined in species richness or abundance in particular locations over periods of several years to a decade or two. That kind of work hasn’t been done on many species at all however, although there was a recent study which looked at total insect biomass over a period of twenty-seven years in Germany, and they observed an eighty percent decline in insect biomass over that period, which is quite striking. They were unable to attribute it to any particular cause. Things such as climate change and habitat degradation are often cited as the reason, in this case they suspect it was possibly an effect of agricultural intensification.
MA: Let’s talk about some of those things. We know that climate change is heating up certain places and causing various types of ecosystem shifts that are making it harder for those organisms that live there to continue. What is causing decline there? I saw you looked at a forested area in New Zealand for example. What do we know about what is happening there and why?
AD: In this particular island, which is called Little Barrier Island, we analysed invertebrates from basically sea level up to the summit using DNA techniques. This is a habitat which is very intact, it has had some forest clearance and impacts such as that at the lower levels back in the 1800s, but unlike most other parts of New Zealand there are no mammalian predators and it is populated with a lot of endangered birds and also things such as the tuatara which is an ancient reptile, and other organisms which are otherwise quite rare, if not extinct on the mainland of New Zealand. So we concluded that there were something in the range of 6000 invertebrate species on this island and that included about 4000 insects, potentially. This was considering both the things that live above the ground and also the invertebrates that live in the soil, which is a part of the ecosystem which is not often examined. So there is actually a lot of invertebrate biodiversity that is in the soil as well as the things you most commonly see such as bees, moths, butterflies, and so on.
MA: How would you compare what you have found in this remote island – where there is not a lot of degradation – compared to another area that might be facing challenges?
AD: When we analysed the invertebrates on the island, we did that by looking at their DNA sequences. So we have got all that DNA sequence data and we can match that up with DNA sequences from other invertebrates collected from other locations. So we can find out if the same species are present in both places or we can use that data to determine how many different species there are, we can compare the number of species on this island versus the number of species in a more degraded habitat. We do actually have data from some other places as well and it appears that the island has considerably higher invertebrate biodiversity than we see in some mainland sites, although we haven’t formally examined that yet.
MA: Do you have a sense in other places of what is causing a decline? And should we be concerned?
AD: The general sense seems to be that it is human development associated factors which are causing declines of invertebrate biodiversity, such as urban development, habitat fragmentation, pollution, agriculture, use of pesticides, that sort of thing. It is the same set of things which feed into the extinction of other groups of organisms such as birds and mammals as well. But the difference with invertebrates is that it hasn’t really been recognised until recently that they are decreasing in biodiversity or biomass. In New Zealand we can say that there is a general decline in invertebrate biodiversity from native forest sites to agricultural sites which is consistent with what has been observed elsewhere and is consistent with these theories about habitat degradation and agricultural intensification.
MA: So how concerning is this to lose the biodiversity, particularly from invertebrates like insects?
AD: I think it is very concerning, actually. There have been some perhaps alarmist estimates that insects will become extinct within a few decades based on current trends. But given the apparent role of invertebrates and insects in all sorts of ecosystem processes that would be very disruptive if that group of organisms was removed from ecosystems everywhere. So it obviously is a very concerning issue everywhere.
MA: Give us some examples. Like suppose we lose a certain number of these invertebrates from an ecosystem, would you be thinking there might be a chance of an ecosystem collapse without them or would there be an adaptation?
AD: My sense is that the effects would be a whole variety of things. I am not sure they would extend to a complete ecosystem collapse. Perhaps at the extreme if there were no invertebrates present whatsoever that would happen, but to give obvious examples: if you removed the pollinator invertebrates from a system then plants would not be able to reproduce and develop. Another example I am aware of is that removing predatory insects from a particular habitat can have an effect, for example, on dung beetles, this changed the degree to which carbon was brought into the soil and made available for primary plant growth and that sort of a thing. So there would be a whole array of different effects depending on the particular invertebrates that were involved.
MA: If you were going to be advising policymakers about where we need to be going from here from a scientific view, what would you say?
AD: I would suggest that some things that could be done would be to try to limit the use of pesticides in agricultural contexts, ensuring that agricultural areas include a range of plants and habitats within that. So you are basically providing a place for the insects to live rather than allowing these monocultures of one crop and then blasting it with pesticides to try to maintain that one crop. We need to have a variety of spaces and resources and a lack of pollution and pesticides in order to enable a rich invertebrate community to exist. So any move in that sort of direction I think will be helpful.
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