Channel-hopping moth plague: our clothes are safe, but mind the cabbages

Callum Macgregor, Newcastle University

The next great plague has descended, and this time it’s moths. Diamondback moths have been crossing the English Channel over the past fortnight in far greater numbers than usual.

Those of you reaching for moth-balls and carpet sprays, stop. There are only two species of British moth (from a cast of thousands) that damage clothes, and the diamondback is not one of them. You, the reader, really don’t need to worry – unless you grow cruciferous vegetables like cabbages or broccoli.

Plutella xylostella – more commonly known as the diamondback – is one of the world’s most widespread and prevalent agricultural pests; so widespread, indeed, that scientists disagree as to where exactly its native range lies.

Their success belongs in part to their preference as caterpillars for eating plants in the Brassicaceae family. This amazing group of crops (notably the species Brassica oleracea) has been selectively bred over hundreds of years to make use of almost every part of the plant, and now contains many popular vegetables such as cabbages, broccoli, Brussels sprouts and turnips, as well as oil-seed rape. The moths lay eggs on brassica leaves; a week later, caterpillars hatch and start eating. An infested plant can quickly be reduced to little more than leaf stems.

Cross-Channel travellers

Despite being one of the smallest moth species to occur in the UK, with a wingspan of under 15mm, diamondbacks are capable of dispersing vast distances, using the wind to make up for their small size. Research has shown that without assistance, diamondbacks are only capable of flying 35 metres – yet when carried along by the wind, they may travel hundreds of miles in a single day.

It is this ability to disperse that leads it to British shores. Every summer, adults cross the Channel and attempt to breed in the UK. A number of butterfly and moth species employ this strategy. In some cases, such as the Painted Lady butterfly, the offspring will return south ahead of the winter. For others, including diamondbacks, the offspring will attempt to remain, but British winters are typically too cold for them to survive.

What’s for dinner? Cabbage, broccoli and Brussels sprouts.
Yuangeng Zhang / shutterstock

For the moths, these fatalities are an unfortunate side effect of a highly dispersive life history; by having offspring constantly travelling beyond the edge of their range and attempting to breed, the moths ensure that no available space is wasted. Should some of the dispersing moths find a new area that is suitable for breeding success, they will benefit enormously from a lack of competition with their peers and, potentially, the absence of specialised predators and parasites. Thus, evolution favours and preserves these intrepid explorers.

Supermoth?

And it is once the moths begin to breed that the problems begin for farmers and gardeners, because these are not your average pest. Diamondback has been referred to in some coverage as a “super-moth”. It’s a title it certainly deserves.

The species has proven itself to be extraordinarily adept at evolving resistance to pesticides. Wild populations have developed significant resistance to almost every significant synthetic insecticide in use, including one of the main classes, pyrethroids.

Perhaps more impressively, diamondback was the first insect recorded to have developed resistance in the field to the bacterial pesticide Bacillus thuringiensis; only one other species is known to have managed this since (the “cabbage looper”, a pest moth named after its favourite food). Interestingly, this has led scientists to target it with the same genetic tools as are employed against the mosquitoes that transmit dengue fever and Zika virus. Field trials are planned in the US for this summer.

Tough times on the veg patch

In the short-term, perhaps. The influx of moths will soon begin to produce larvae, and these may cause substantial damage to crops where they are able to escape death by insecticide. The damage will be most severe to farmers of leaf crops, such as cabbages or kale, as the holes left behind in leaves by caterpillars make the crop unsellable.

Diamondback caterpillars leave cabbage unappetising and unsellable.
Rothamsted Research, CC BY

Looking at the longer term, this year’s invasion will die out over the winter. Next year there will be another, but this is nothing new: these moths come to the UK every year in substantial numbers. I spent the summer of 2014 collecting moths on farms in Oxfordshire for a study on the effects of light pollution on moths. Out of the 203 species of moth I recorded, diamondback was the 26th most common, forming around 1% of my total catch.

Britain’s cabbage-growers have been dealing with diamondback for years and have managed to persist thus far. They may have a hard summer ahead of them but it is not without hope. Although globally diamondbacks have developed resistance to almost all pesticides, most populations are only resistant to a subset of these, and scientists at Rothamsted Research are already studying the current influx to identify their weaknesses. Armed with the results of that research, farmers may be capable of restricting the damage.

The Conversation

Callum Macgregor, PhD Candidate, Newcastle University

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

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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.
from http://www.shutterstock.com

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 

Three steps to save Britain’s butterflies

British populations of butterflies, including some of the most familiar countryside species, will begin disappearing within decades unless we take action. This is the alarming conclusion of new research published in Nature Climate Change by a group of British scientists.

Butterflies are naturally sun-loving creatures, and with the UK sat on the northern edge of many species’ ranges, previous studies have forecast possible benefits to UK populations from a warming climate. However, as the climate changes, extreme weather events including droughts are expected to become more common. Droughts can be a problem for butterflies, especially if they harm the plants upon which caterpillars rely for food. With less food around, populations can crash, and may take several years to recover to pre-drought levels.

The new study used models to predict the frequency of droughts like that of 1995 under different scenarios of greenhouse gas emissions, and examined factors affecting the likelihood and speed of recovery for populations of six species of butterflies that experienced population collapses after the 1995 drought.

While droughts as severe as 1995 have previously only occurred as little as once in 200 years, allowing plenty of time for butterfly populations to recover, the study found that they may become far more frequent. If greenhouse gas emissions continue to increase at current rates, they might even occur on average once every 1.29 years (effectively every summer).

The red admiral is one of the UK’s most common butterflies.
Kenneth Dwain Harrelson, CC BY-SA

Under “business as usual” scenarios, the research forecasts the widespread extinction of local colonies of butterflies as soon as 2050. So, what can be done to conserve our butterflies? Here is my simple, three-step guide:

Step 1: stop global warming in its tracks

Butterflies don’t have to be colourful.
Soebe, CC BY

Clearly, reducing the impacts of climate change will be important. Delegates from around the globe will meet in Paris later this year for the 2015 UN Climate Change Conference, hoping to reach the first deal on reducing emissions since Kyoto 1992. Under the study’s best case scenario for emissions, 1995-like droughts might occur only every six to seven years, giving butterfly populations much more opportunity to recover in between.

Step 2: protect butterfly habitats

Ensuring the availability of suitable habitats for butterflies can also make a big contribution. The researchers found butterfly populations were more likely to persist through droughts and recovered more rapidly if situated in areas with larger, less fragmented patches of semi-natural habitat, such as grassland. Larger areas are likely to contain more abundant and diverse food-plants, helping more species of butterfly, and can also better resist edge effects associated with drought, such as moisture loss from woodland.

Highly fragmented habitats have more edge relative to their area, and therefore experience more severe edge effects. Well connected habitats, through which butterflies can easily mingle and locate breeding sites, could add decades on to the survival of certain populations as the climate warms.

Buddleia, also known as the butterfly bush, is one of the UK’s best plants for encouraging butterflies.
Andy Fogg, CC BY

Step 3: create more butterfly-friendly gardens

While large-scale habitat management programmes, such as the establishment of nature reserves, are an important means to preserve semi-natural habitat, the restoration of connectivity is where butterfly enthusiasts can help at home.

According to Richard Fox from the charity Butterfly Conservation, many drought-prone species can be encouraged to breed in gardens by leaving grass to grow long. “You don’t have to let your prize lawn go to rack and ruin, you can just leave a strip along the fence”, Fox told me. Depending on how much is left, this could provide breeding habitat for species including the speckled wood, ringlet, meadow brown and large skipper.

A female speckled wood butterfly
Charles J Sharp, CC BY

Meanwhile, other species can be helped by choosing garden flowers with care, or letting them choose themselves. “Large and small white will breed on Nasturtiums and love to nectar on flowers like buddleia and perennial wallflower,” advises Fox, while “green-veined white caterpillars can feed on lots of weeds, so not being too tidy can help”. If you have a garden, why not plant some butterfly-friendly plants of your own?

So while butterfly lovers will be among those waiting with bated breath for the outcome of the Paris summit, they may also be able to help closer to home. Habitat availability will be vital to the survival of butterflies when drought strikes, and by providing such refuges in back gardens anybody can help them survive and flourish.

The Conversation

Callum Macgregor, PhD student in Ecology, University of Hull

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

Coming out of the closet: why I will always love moths

Ask people to describe what they associate with butterflies, and you will probably get an image of a sunny summer’s day, with a beautiful peacock drifting gently on the cooling breeze.

Ask the same question but for moths, and you are more likely to be told about holes in a favourite woollen jumper, or something small and brown beating itself to death against a bathroom light fitting. We don’t view moths with the same affection as their day-flying cousins, and the irrational fear of moths is even common enough to have a name: mottephobia.

To my mind, this is unfair. Let’s start with the clothes-eating accusation. According to the charity Butterfly Conservation (which also protects moths), there are around 2,500 species of moths found in the UK; of these, only two will attack clothes. They prefer dirty items in undisturbed places: that means that if your jumper has been attacked, you probably weren’t wearing it often enough anyway.

In fact, there are also moth species that are crop pests, such as the diamondback moth, and some which produce irritant hairs as caterpillars – the non-native oak processionary moth currently infesting London is one such example. But again, these examples are very much in the minority among the total diversity of moths, and there are very many more reasons to love moths than to hate them.

Birch or buff-tip?
Callum Macgregor, Author provided

Many moths are just as beautiful as butterflies; some even look like butterflies! A particular favourite of mine is the brimstone moth: exactly like the brimstone butterfly, it is so-called for its vivid sulphur-yellow colour. Some are superbly camouflaged, like the buff-tip – easily mistaken for a broken twig of silver birch. And some have attractive names to match their appearance, such as the fabulous Merveille du Jour (“marvel of the day”), pictured at the top of this article.

Moths are vital pollinators

But beyond their beauty, moths also perform vital roles in the natural communities to which they belong. Along with colleagues, I recently examined the scientific literature to establish how important moths are to flowering plants as providers of pollination services. Most moth species that feed as adults do so by drinking nectar, and in doing so accidentally carry pollen between flowers.

We found examples of moths serving as important pollinators across many important habitats and in every continent except Antarctica. Several studies suggested that moths were the second most important pollinators in the area surveyed, behind only bees. In the UK, moths might be pollinating wildflowers near you including honeysuckle, bramble, white campion, wild carrot, thistle and ragwort. In North America, moths pollinate many types of cactus, and milkweed (beloved of caterpillars of the monarch butterfly). Globally, they are also well-known pollinators of many orchid and lily species.

If you’re a bird or a bat, a moth makes for a tasty treat. Researchers from the University of Bristol have examined the diet of two species of long-eared bat in England, revealing that their main food source was large-bodied moths from the Noctuidae (or owlet moth) family. Whereas bats (and the eerie nightjar) eat adult moths, moth caterpillars provide a vital food source in the spring for young birds including blue tits, which can munch their way through 35 billion caterpillars in the UK every year.

The moth-munching blue tit.
OliBac, CC BY

Especially important in this regard are those moth species that are active as adults through the winter, including the aptly named winter moth; these species reach the caterpillar stage of their life cycle at exactly the right time of year for busy blue tit parents to exploit.

And did you know that one species of moth has been domesticated into a valuable commercial livestock species, at the centre of a multi-billion dollar global industry? When spinning a cocoon in which to undergo the transformation to an adult moth, the caterpillars of the domesticated silkmoth Bombyx mori produce lustrous threads several hundred metres in length. These threads, once unravelled, are spun into the fine textile silk.

And if none of this has convinced you, know this: butterflies are actually just a minor subset of moths!

The Conversation

Callum Macgregor, PhD student in Ecology, University of Hull

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