Insects are declining – but talk of “insectageddon” is premature

I originally posted this blog on the Nature Ecology & Evolution community forum; you can read the original version here.

Recent research showing severe declines in biomass of flying insects has been much-discussed in the literature and the global media. In a new study of a long-term insect population dataset, we found that the biomass of moths increased before it declined, and remains higher now than in the 1960s.

Insects play a number of vital roles in our ecosystems, and as a consequence, several studies in recent years that have reported sharp declines in their “biomass” (combined weight) have been greeted with alarm by the media and public.

However, the conclusions of these papers have been met with scepticism by the scientific community. There is a widely-held opinion that studies on insect biomass have so far been based on too little data to be certain of their conclusions, variously having too few separate sampling sites, data from too short a time period, or from only the beginning and end of a sequence (rather than continuous data), or data collected with a non-standardized method over time.

To try and understand patterns in insect biomass change over time in a more robust way, overcoming some of these criticisms, my colleagues and I turned to the long-running network of moth-traps of the Rothamsted Insect Survey (RIS). Rothamsted currently operate around 80 identical moth-traps across the UK and Ireland, each of which collects moths (which are then identified and counted) on a nightly basis using a standardized methodology. From among these, we identified 34 traps that had operated continuously for at least 30 years in the 51-year period since the trap network commenced in 1967.

Peppered Moth (Biston betularia) has declined in abundance by 81% since 1967, according to the Rothamsted Insect Survey’s data.

To translate the abundance records collected by the RIS into estimates of biomass, we first needed to know how much each moth weighed. Rothamsted don’t retain every moth they capture, and catching and weighing a representative sample of every species in their database would be prohibitively labour-intensive. Existing dry body mass data weren’t available for most British moth species either, but field guides do list typical forewing lengths for every species as an identification tool, so we resolved to model the relationship between these two variables.

Thanks to the hard work of summer project student Becci Kinsella, we collected an empirical dataset on the forewing length and body mass of 600 individual moths from 94 species and, fitting a model to this data, estimated the body mass of over 1000 species of larger moths. Amazingly, we found this allowed us to predict around 90% of the total variation in the biomass of mixed-species samples of moths.

Next, Masters student Jonny Williams applied these estimates to data from the 34 long-running traps from the RIS, generating annual estimates of moth biomass from each trap. The results were astonishing. We found that the average biomass of moths sampled annually by each trap had approximately doubled over the 50-year duration of our dataset. This was not a simple increasing trend, either: biomass had increased steeply between 1967 and 1982, but gradually declined thereafter. The 10% per decade rate of these more recent declines actually matches up well to the findings of other recent studies of insect abundance and biomass (none of which commenced earlier than 1976), but the overall longer-term pattern of steep increase, then gradual decline does not support the widely-suggested scenario of “insect Armageddon”.

Abundance of the Large Emerald (Geometra papilionaria) reached a peak in 1983, matching the trend for moth biomass as a whole.

To understand drivers of these recent declines, we turned our attention to land-use, categorising sites into four groups: arable, grassland, woodland and urban. Two drivers of environmental change that are often mooted as potential causes of insect decline, especially for moths, are agricultural intensification (most relevant in arable sites) and light pollution (most relevant in urban sites); but we found that the steepest post-1982 biomass declines were in grassland and woodland.

The third of the “usual suspects” is climate change. A strong degree of synchronisation in both year-to-year biomass change and longer-term trends between sites, land-use types, and taxonomic groups of moths, pointed the finger of blame squarely towards factors that operate across all land-use types, such as temperature and rainfall. Yet surprisingly, we found no relationship between either of these variables and biomass change. However, two of the biggest periods of biomass change – a strong increase in the late 1970s and a decline in the late 1990s – directly followed the heatwave/drought years of 1976 and 1996. It seems possible, therefore, that extreme climatic events can perturb populations and communities, with resultant ecosystem feedbacks causing subsequent biomass change – an avenue for further research, perhaps.

Finally, we resampled the full RIS dataset to investigate the influence of data structure on estimates of insect biomass change, taking every possible subset of data of over 5 years’ duration, both for single study sites and the full 34 sites combined. It’s well-known that insect populations can fluctuate wildly from year to year, so unsurprisingly, longer spans of data were less likely to estimate massive increases or declines. Likewise, biomass changes were larger at single study sites than across the full dataset of 34 sites. Many studies rely on single return visits to previously-sampled locations, generating an estimate of biomass change between two points in time. Unfortunately, when compared to the trend fitted by a linear model through annual estimates over the same time periods, we found the two-sample approach incorrectly estimates the direction of biomass change in a quarter of cases. Lastly, it’s unwise to hang your hat on biomass change since an arbitrary start date, since patterns change over time: within our study, biomass increased since 1967, decreased since 1982, but has been roughly stable since 1997.

These findings emphasize the vital importance of long-term, standardized data collection for understanding population change. Several UK initiatives, like the RIS and the UK Butterfly Monitoring Scheme, have been doing this for decades on home soil, but globally very few such datasets exist, particularly in the tropics. Establishing long-term monitoring at a much broader scale is a challenging prospect, but a worthy goal.

Pollinators: switch street lights off at midnight to help moths and nocturnal wildlife

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Callum Macgregor, University of York

Conservation is often a conflict between the demands of development and a desire to do what is best for the environment. It’s rare that we get the chance to report a decision which was taken for the good of people that has also panned out well for nature’s ecosystems. However, that is just what our new research paper found.

Saving energy from street lighting is not just a green option, it also makes good financial sense. Two solutions in particular include replacing old High-Pressure Sodium (HPS) lightbulbs with new and energy-efficient Light-Emitting Diodes (LEDs) and turning the lights out entirely during the latter part of the night when fewer people are around. In the UK, these changes in lighting technology have been gradually taking effect over the last decade or so.

While these decisions were made for good reasons, we knew little about how they would influence nocturnal wildlife. Our team of experts at York and Newcastle universities were interested in finding out how moths might be affected by the switchoff and new LED lighting, as they play an important role as night-time pollinators of a wide range of flowers, and have declined in abundance by 40% in 40 years.

Moths are important pollinators but have endured significant population declines in recent years.
Safwan Abd Rahman/Shutterstock

Light pollution, from street lights and other sources, has been suggested as a possible cause of this decline, though there are other factors such as climate change and habitat loss.

Our previous research showed that under HPS street lighting left on all night, moths were distracted from visiting flowers and instead flew higher up, around street lights. This resulted in less pollen being carried by moths in lit areas, and a subsequent study by Swiss researchers demonstrated that this actually caused reduced fruit production.

Read more:
Fatal attraction: how street lights prevent moths from pollinating

In our study, we asked whether the disruption to nocturnal ecosystems from street lights might be eased or exacerbated by the introduction of new energy-efficient LED street lighting. Working on farmland in East Yorkshire in the UK, we set up a chain of mock street lights alongside hedgerows that would allow us to manipulate the type and duration of lighting.

Older and less energy-efficient HPS lighting near wildflowers.
Callum Macgregor, Author provided

We compared older HPS lights to LEDS, and standard full-night lighting to part-night lighting, in which lights were turned off at midnight. All lighting was compared to an unlit control that replicated natural darkness. Under each lit and unlit treatment we placed several plants of White Campion (Silene latifolia), a common wildflower known to be pollinated by both bees and moths. We left each plant in the field for four days and nights before measuring what proportion of flowers had been pollinated, and the weight and number of seeds in every fruit.

LEDs are rich in blue light which is attractive to moths but we found no difference in the rate of pollination between plants under LEDs and those under HPS lights. Our data did show that the differences between pollination under full-night lighting and in natural darkness were erased when lights were turned off at midnight.

Newer and more energy-efficient LED lighting near wildflowers.
Callum Macgregor, Author provided

Surprisingly, this wasn’t just a partial improvement. We found no significant difference between rates of pollination in part-night lighting treatments and in natural darkness, and this suggests that turning lights off at or after midnight may allow nocturnal ecosystems to function as normal in the second half of the night.

These results are quite encouraging. Local authorities can save money and energy from street lighting and help nocturnal ecosystems recover from light pollution at the same time.

So there’s no evidence that the switch from HPS lights to LEDs increases the negative impacts of lighting on wildlife, and even better, switching to part-night lighting actually appears to reduce them. By switching lights off at midnight there is the potential to tackle two issues at once – reduce energy bills and the ecological impact of light pollution.The Conversation

Callum Macgregor, Postdoctoral research associate, University of York

Moths expert: match report on Ronaldo insect encounter at Euro 2016 final

Callum Macgregor, Newcastle University

After a month of football, Euro 2016 drew to a close with Portugal defeating France 1-0 in extra time to lift the famous trophy for the first time. But the final game was a turgid affair, and perhaps the image most likely to endure involved a rather unexpected participant.

As Cristiano Ronaldo sat in tears on the turf, the reality of his game-ending injury sinking in only 25 minutes into the game, a moth fluttered around his eye and settled on his forehead. This moth was one of thousands in the stadium, pictured in clouds on the pitch as the players warmed up, and being swept with brooms from advertising hoardings.

What were they doing there? The bizarre spectacle appears to have been the result of a coming together of several exceptional circumstances.

A very brightly lit stadium

It is commonly known that moths display an extremely strong attraction to sources of artificial light, although we still don’t really know why. The stronger and brighter the light, the better – and this is our first exceptional circumstance.

Fully lit, the Stade de France shines like a beacon even amid the glow of La Ville Lumière. Worse yet, the format of the lighting – in a ring, facing inwards – means that once a moth finds itself inside the stadium, it would be near-impossible for it to escape the influence of the lights.

One large moth-trap.
Srdjan Suki/EPA

But many football games have been played under floodlights at big stadiums, and this game began while it was still daylight. This brings us to our second exceptional circumstance, then – the stadium lights were left on overnight on the eve of the game, presumably to aid the ultra-tight security effort that has surrounded the whole tournament.

The lights had a full night to attract as many moths as they could into the stadium. When fans and players began to arrive, those moths were nearing the end of their daytime slumber.

Migration spectacular

Still, though, brightly lit stadia have held events on consecutive nights before without experiencing mothy visitations. So to find the third exceptional circumstance, we need to look more closely at the moths themselves.

As the game unfolded, it became clear to those in the know that the vast majority of moths on display were representatives of a single species: Autographa gamma, the Silver Y – both names stemming from the γ-shaped marking on the wing. The Silver Y carries metallic patterns on its wing, like many other species in its sub-family, the Plusiinae, including the beautiful Gold Spot and my personal favourite species, the Burnished Brass.

When not bugging footballers, Silver-Ys enjoy feeding on flowers.
Arto Hakola/Shutterstock

Importantly for our investigation, these moths bear a remarkable similarity to another species recently making headlines, the cabbage-chomping Diamondback moth, which also migrate in huge numbers to UK shores.

Silver Ys make the journey annually from North Africa, travelling through France (including Paris) to breed in Britain. Scientists at Rothamsted Research found that in peak years they number almost a quarter of a billion, and up to four times that number return southwards in the autumn. By a twist of fate, the Euro 2016 final appears to have coincided with this year’s migrating Silver Ys reaching Paris on their northward journey.

Bad news for moths?

We know from several recent studies that the profusion of artificial light at night spells trouble, both for moths and the other organisms they interact with in the ecosystem. Moths have short lifespans – Silver Ys may spend as little as two weeks in their adult form after emerging from the cocoon – and in this time must complete their migration before finding a mate and a suitable location for their eggs. Time spent under the influence of a light is time wasted.

With luck, organisers at the Stade de France will have the sense to leave the stadium lights off on Monday night. Returned to (relative) darkness, most of the stadium’s temporary lodgers will be able to escape the arena and continue their journey merrily northwards – perhaps, for some, to land on British soil within the coming days much to the excitement of moth lovers who, like me, eagerly await their arrival.

The Conversation

Callum Macgregor, PhD Candidate, Newcastle University

This article was originally published on The Conversation. Read the original article.

Fatal attraction: how street lights prevent moths from pollinating

Callum Macgregor, University of Hull/Newcastle University

For centuries, we have observed that artificial sources of light hold a strange fascination for moths. Despite decades of research, we still don’t know the cause of this attraction. Some theories put it down to the way moths navigate; others think it’s a mechanism to help them to escape from perceived danger. But the truth is, little evidence exists to support either of these ideas.

Whatever the cause is, research has shown that this deadly attraction may have even more sinister consequences than we first thought. In an open access paper in Global Change Biology, my colleagues and I describe the first evidence which shows that the effects of artificial light on moths may have serious implications for the wider ecosystem.

There has been plenty written about the danger posed by declining bee and butterfly populations, on the basis that some plants rely on these insects to carry pollen and fertilise flowers, in order to reproduce. But many people aren’t aware that moths also perform this task: our study of field sites across Oxfordshire found that one in four moths were carrying pollen, from at least 28 different plant species.

Danger zone.

And like their cousins the butterflies, moths are in trouble: according to Butterfly Conservation’s Richard Fox: “the total abundance of moths in Britain has decreased by over a quarter since the 1960s”. Research indicates that artificial light, such as street lamps, has contributed to this decline by affecting moths’ development, reproduction and ability to escape predators.

Now, our data suggests that street lights are also directly thwarting night-time pollination, by attracting moths upwards, away from the fields and hedgerows. We found that the abundance of moths at ground level was halved in lit areas, while flight activity at the height of the street light was nearly doubled. The diversity of species was also reduced at ground level, with 25% fewer moth species in lit areas, compared to places without street lighting.

This change is likely to disrupt nighttime pollination by moths, and indeed we found some evidence that moths may carry less pollen, from fewer plant species, in lighted streets. This could mean that the impacts of street lights go beyond posing a health risk to moths. Plants that rely on moths for pollination would also suffer if their reproduction is impeded – and this might, in turn, affect organisms that eat those plants or drink their nectar.

In a best-case scenario, some of these so-called cascading effects might be mitigated where flowers can rely on other insects such as bees for pollination. But there are further factors driving declines in pollinator populations, such as climate change, pesticides and habitat loss. Now, our research suggests that artificial light can be added to the list.

Unnatural selection

So how can we protect these beautiful, under-appreciated insects and the important role they play in our environment?

The Spindle Ermine moth knows what’s good for it.
gailhampshire/flickr, CC BY

Another recent paper published by researchers in Switzerland suggests that moths may be evolving to be less strongly attracted to lights. Under controlled experimental conditions in a flight cage, they found that Spindle Ermine moths from urban populations were less likely to be captured in light-baited moth traps than their rural counterparts.

These findings suggest that moths which can resist the temptation of lights put themselves at a significant advantage over their peers. Over time this has led city-dwelling moth populations to become less attracted to lights, through natural selection. But this is all relative: urban moths are still far from immune to the deadly allure of urban street lights.

We can’t simply switch street lighting off: although the evidence for its actual benefits is questionable, it certainly contributes to many people’s feeling of safety and security when outside after dark and proposals to turn lights off are often unpopular.

But if we don’t wish to wait for the slow crawl of evolution, it may be that recent advances in street lighting technology can help to mitigate the impacts of artificial light. For example, developments born out of a desire for energy efficiency could also minimise the impact of street lighting on moths. Measures such as switching on street lights for part of the night, dimming them or introducing motion-activated lighting would reduce moths’ exposure to street lights. Similarly, the flexibility of LED lights might allow for the creation of street lights that are less attractive to moths, which respond most strongly to short-wavelength blue light.

Nevertheless, artificial light at night continues to increase as we seek to drive darkness from the streets. Our research is another warning that this may have far-reaching consequences for the organisms around us.

The Conversation

Callum Macgregor, PhD Candidate, University of Hull

This article was originally published on The Conversation. Read the original article.

Street lights alter moth activity

This post was originally written for the Butterfly Conservation blog and focuses on the contribution this marvellous charity makes to our research on moths, pollination and light pollution.

Newcastle University PhD student Callum Macgregor explains how a new study has revealed that street lights alter the activity of moths.

The findings of the study, an Open Access paper published today in the scientific journal Global Change Biology, could have potentially serious implications for wildflower species. 

The study forms part of a three-and-a-half  year research collaboration between Butterfly Conservation, the Centre for Ecology and Hydrology (CEH) and the Universities of Newcastle and Hull.

Small Elephant Hawk-moth with Greater Butterfly Orchid pollinia (John Bebbington)3
Small Elephant Hawk-moth carrying Greater Butterfly Orchid pollen. (c) John Bebbington

It is widely accepted that butterflies are among the most important groups of pollinators but the majority of our species of Lepidoptera are moths. As a PhD student co-supervised by Butterfly Conservation staff, my supervisors and I have set out to establish the importance of moths to pollination in the UK and abroad. In a paper published last year (which you can read here), we reviewed evidence from around the globe that moths are important pollinators of a diverse range of plant species, including some evidence of a role in the UK.

Butterfly Conservation’s 2013 report The State of Britain’s Larger Moths showed that our native moths are in trouble, with two-thirds of widespread and common macro-moth species in decline over the last 40 years.

Among the likely causes of this decline is the continuing increase in the use of artificial light at night to illuminate our streets, parks and gardens. Moths are known to be attracted to sources of artificial light and there is a growing base of evidence that this could affect their growth, reproduction and ability to escape predators. We were interested in whether the effects of artificial lights on moths could alter their role as pollinators.

Our research revealed that moth activity in street-lit areas shifts from vegetation level to lamp-post height, with lights attracting moths away from the fields and hedgerows. Moth abundance at ground level was halved in lit areas but flight activity at the height of the street light was nearly doubled. Around a quarter of moths were carrying pollen (from at least 28 plant species), supporting the idea that moths make an important contribution to pollination in the UK. However, we found some evidence that moths may carry less pollen, and from fewer species, in street-lit areas.

Dr Darren Evans of Newcastle University, one of my lead PhD supervisors, compares these findings to worries about more well-known pollinators, bees and butterflies. he said: “There is a great deal of concern at the moment about our falling pollinator populations and the knock-on effect on plant pollination. Our research suggests that it’s a process that is being damaged on two fronts – night and day”.

The project is funded under the NERC Industrial CASE studentship scheme, which aims to place PhD students into “mutually beneficial research collaboration between academic and non-academic partner organisations”. Acting as the CASE partner on the project, Butterfly Conservation staff including Head of Recording Richard Fox, Zoe Randle, Les Hill, Mark Parsons, and Director of Conservation Nigel Bourn have all been able to advise and shape this research.

Richard in particular is one of my PhD supervisors and a co-author on the paper. He said: “Moths are an important part of the UK’s biodiversity, as pollinators of wild flowers and as food for many birds and predators. The role of artificial light in causing moth declines remains unclear, but this new research indicates effects not just on moths but on the whole ecosystem”.

We hope that our findings can help to conserve this beautiful and charismatic group of insects and the flowers that depend upon them. Dealing with an issue such as street lighting can be complex:

Dr Michael Pocock of CEH, my other lead supervisor, said: “Street lighting at night is important for road safety and people’s security but our research is just the latest piece of evidence showing the unintended negative effects of street lighting on wildlife”. We are now investigating a number of recent advances in technology, such as the rise of LED street lighting, to see whether they may offer opportunities to reduce these negative effects.

Follow me on Twitter @Macgregor_Cal