Big science from small insects
Anniversaries are often a time to look back. But after taking stock of the past, it can be just as important to look to the future.
2014 saw the fiftieth anniversary of the Rothamsted Insect Survey (RIS) that has collected and catalogued more than 30M insects across the UK – information that informs farmers of when pest species might hit their crops, what animal disease vectors are flying, and is used by ecologists detecting the patterns that underpin the structure of biological communities.
Yet after 50 years its work is far from done. Indeed, the data become more and more valuable as the time series increases. As a changing climate alters the distribution and abundance of important crop pests, continued monitoring of new insect threats to economically important crops such as cereals is crucial. Many of the insects, principally aphids, also carry viral diseases that further undermine aspects of the UK's food security.
"The Rothamsted Insect Survey has amassed an incredible wealth of data and is now widely regarded as the most comprehensive and continual database in the world on terrestrial invertebrates," says RIS Project Leader Dr Richard Harrington from Rothamsted Research, an institute that receives strategic funding from BBSRC.
Supporting the survey's work into the 21st century, RIS is now funded as a BBSRC National Capability – an institute-based resource intended to benefit the wider scientific community. It designates the RIS as a repository of data and expertise that can be used by scientists in the UK and across the world.
Indeed, suction-traps of the RIS design are spreading across the world as other countries develop similar surveillance and warning mechanisms, opening opportunities for collaboration between growers and industry with entomologists interested in the fundamental mechanisms behind the spread of insect populations.
It was fifty years ago today
When legendary entomologists L.R. 'Roy' Taylor and C.G. 'Johnny' Johnson flicked the switch on the first insect suction-trap in continuous operation at Rothamsted on 29 April 1964, they might have wondered if their project would still be going after 50 years, and what the world would be like: that day there was a US nuclear test in the Nevada desert; the Beatles had three singles in the top five in America.
Elements of the work had begun just before the Second World War with the development of a different type of trap – the light-trap to capture moths – by their colleague at Rothamsted, the entomologist C.B. Williams. Twenty years later, and against the backdrop of an explosion of concern at the effect of pesticides on wildlife following the release of Rachel Carson's book Silent Spring in 1962, the researchers proposed expanding and developing the trap network nationwide: a likely and immediate benefit could be the ability to warn farmers when pest infestations were unlikely, saving them from spraying chemicals and thus reducing insecticide use.
The scientists also realised that a trap network could help investigations on the migration and population biology of insects, including those of importance to agriculture. Funding from BBSRC's forerunner the Agricultural Research Council (ARC) supported the development of the twin trap network across the UK: a series of 12.2M suction-traps to trap aphids and other flying insects, and light-traps to capture moths that, although it was not fully realised then, are very good barometers of environmental quality.
Here, there and everywhere
The RIS now provides the most extensive standardised data for any terrestrial invertebrate groups anywhere in the world. It has contributed to studies on the drivers of biodiversity, insecticide resistance, ecological community structure, aphid morphology and climate change – all topics of relevance to research on agriculture and food security. (See Research Impacts below.)
From 2012 RIS has been funded as a BBSRC National Capability (approximately 60% of the £500,000 annual running costs), along with much needed support from the agricultural industry, especially the British Beet Research Organisation and the Home Grown Cereals Authority and from Rothamsted's Lawes Agricultural Trust. RIS data have also formed the basis of a wide range of specific research projects funded by BBSRC, NERC, Defra (Natural England), the EU and others.
The major target of the suction-traps seen in the video above are aphids. A meta-analysis has reported average yield losses of 10% from feeding damage by aphids across a range of crops. If virus damage was considered, this figure would rise, but a 10% yield loss across the ~3.8M hectares of cereals and oilseed rape grown in the UK would cost upwards of £300M – a figure that could be much higher if damage from aphid-transmitted viruses was included.
According to the PUSSTATS, approximately £3M hectares of cereals are treated with insecticides (including seed treatments, active area sprayed). This will cost millions of pounds, and everytime growers and farmers can delay or reduce insecticide use, they save money and can be more competitive, as well as avoiding potential environmental problems such as killing beneficial natural enemy insects, or encouraging insecticide resistance.
From volunteers to working with industry and government, RIS has been a story of collaboration. Gathering such a vast amount of data has led to some innovative ways to collect and catalogue the insect samples. Long before the term 'citizen science' was invented, the RIS recruited volunteer insect enthusiasts to identify species of moth from the light-trap network.
Harrington says there are now approximately 100 volunteers working on the RIS project (with 5 full-time employees) and there have been around 500 volunteers over RIS' 50 years; some individuals have been contributing their services – for free – for more than 40 years. Nowadays such efforts to 'crowdsource' scientific data are popular and increasingly common, and the RIS was a very early and successful pioneer of the concept. (See more on BBSRC-funded crowdsourcing projects in the Can you spot the bird? and Fraxinus video features.)
After the samples are recorded, all insects from the suction-traps are stored. "They are an invaluable resource for studies of, for example, the natural enemies of aphids such as ladybirds and lacewings, wasps, the mosquito vectors of West Nile virus, and the midge vectors of Bluetongue virus of sheep and cattle," says Harrington. RIS data were used by researchers at the Pirbright Institute (then called the Institute for Animal Health, which also receives strategic funding from BBSRC) to study the dynamics of the Culicoides biting midge disease vectors using specimens from the suction-trap network.
The UK Government (through FERA) and the agricultural industry have developed complementary systems. "The yellow water pan traps run by FERA are complementary to our suction-trap system and we work together. Their system provides very local information for participating growers," says Harrington, adding that the RIS is conducting a grower survey as part of its work with BBRO in late 2014.
The success of the network has seen elements of it spread around the world, and suction-traps of the Rothamsted design have made it as far as China, New Zealand and South Africa. Harrington is therefore looking to expand on the EU funding in the past, which led to a common insect survey database and several joint publications.
"We will seek EU/other international funding for further international collaboration," he says. "It will involve much more work below the species level in the future and an increasing molecular component."
This includes, for example, recognising cryptic species or subspecies which may vary in their pathogenicity to crops. The RIS team also hopes to monitor and identify the presence of plant- and insect-killing viruses in invasive species, and assess and predict changes in genetic characteristics in aphids in relation to changing environmental and agronomic factors.
"We also believe that we have the capability to chart trends in a range of pollinators, which could support those looking at whether and why pollination services are reducing," he says. The proposed work on pollinators would complement and feed into other past and future BBSRC projects investigating the role and importance of pollinating insects in ensuring food security, and other ecosystem services.
Forecasts and pest control
RIS researchers have found strong relationships between winter temperature and the time that aphids first appear in the suction-traps, and their abundance. These relationships are used to forecast when pest aphid movement into crops is likely to start, and to predict the impacts of climate change on pest problems. The wealth of data over time has revealed that compared to 50 years ago, many aphids are flying a month or more earlier. These findings are disseminated in web and email bulletins that are issued on Fridays, picked up by relevant media, and then used by practitioners to guide aphid control programmes.
Individual aphids are tested for their resistance to a range of insecticides; in particular major pests the peach-potato aphid Myzus persicae and English grain aphid Sitobion avenae. Molecular tools are used to detect the genetic mutations conferring resistance, and the findings are fed back to researchers in academia and industry. Recent analysis at Rothamsted has shown that resistance to pyrethroids is increasing in both England and Scotland.
Aphids are particularly important vectors of crop viruses, which lower yields. RIS workers detect the presence of certain viruses in aphids and hence their potential as vectors. The traps in Scotland provide data in support of the Scottish Seed Potato Classification Scheme.
Pest insect population dynamics
Analysis of 5715 series of annual moth and aphid species abundance showed, for the first time, the critical importance of RIS' long time series data in the ability to detect density dependence – an important cornerstone of population dynamic theory that can be used to model and predict insect populations in space and time.
Testing theories of biodiversity
RIS data were used to test a controversial new theory of the dynamics of biodiversity; this 'Unified neutral theory of biodiversity and biogeography' was based on the assumption that trait differences between trophically similar species (growth rates in aphids for example) had no impact on their relative abundance or speciation rates. Data from RIS' moth light-trap network tested the model but did not fit well because ecological communities fluctuated more than expected.
Aphid winter attrition
The temperature at which aphids die is crucial to their overwintering success – it affects how they will infect crops. Aphids were known to supercool and to freeze at temperatures below -20C, but data from the suction-trap network suggested much higher temperatures were causing significant mortality to the mobile forms, probably as a result of membrane disruption.
Effects of climate change
RIS data have been used to detect effects of climate and other environmental changes on the abundance and seasonality of aphids and moths. They have found that, increasingly, aphids are overwintering in the mobile stages as opposed to laying eggs. Climate change is also implicated in some recent moth declines.
Evolution of plant defences
Europe-wide suction-trap data, combined with laboratory selection experiments, showed that different types of Arabidopsis thaliana, a plant much used in lab experiments, are selected according to the relative abundance of two specialist aphid species. This is significant because it demonstrates that pests can directly affect how their host-plants evolve in relatively short spaces of time.
- 1964: Official start of the Rothamsted Insect Survey (RIS) on 29 April, when the first suction-trap begins operating at Rothamsted
- By 1968, 60 moth traps are in place throughout the UK
- 1970s: Suction-traps of the Rothamsted design deployed by entomologists in other countries, first France in 1978
- 1976 sees the peak number of light-traps: 155 (now 84)
- 1979 sees the peak number of suction-traps: 24 (now 15)
- In the 1980s travel funds enable researchers across Europe to meet and form the informal EURAPHID group to share and utilise data and methodologies
- After the Fifth International Symposium on Aphids held in 1997, Spain, a workshop on suction-trapping is held in 1998. These events reinvigorate international collaboration
- 2000-2003 The EU-funded EXAMINE (EXploitation of Aphid Monitoring IN Europe) project establishes a common database for deposition and retrieval of data from the now Europe-wide suction-trap network
- 2000s many papers published on the impacts of climate, land-use and pollution on the dynamics of aphids, moths and other insects
- After an outbreak in 2008 of bluetongue, a deadly disease of sheep and cattle, RIS researchers work with scientists from The Pirbright Institute to study the dynamics of the disease vectors, Culicoides biting midges, using specimens from the suction-trap network
- From 2012 RIS is funded as a BBSRC National Capability
- 2013: Delegates from 12 countries including China, South Africa and New Zealand attend a meeting of the Nordic Association of Agricultural Scientists in Sweden to provide an update on suction-trapping around the world and discuss more potential collaboration
- From 2013 a new database (known as 'Paul') is recommended as a databank and as a means to facilitate collaborative analyses. All Rothamsted and EXAMINE data from the suction-trap and light-trap networks are uploaded and further functionalities developed throughout 2014
- Two species new to science found by the Rothamsted Insect Survey: an ichneumonid (parasitic wasp) and a trichocerid (winter gnat). Neither yet has a published name
- Total number of aphids to the end of 2013: 18,720,533
- The highest number of aphids in a year was 1,082,509 in 1979
- 51,136 aphids were caught in a single trap at Broom's Barn, 26 July 1979, the highest ever recorded in a day
- 478 different aphid species have been identified from the suction-traps
- Total number of moths found to the end of 2013 is 12,243,842
- The highest number of moths in a single year was 629,868 in 1977
- 1535 distinct moth species have been identified from the light-traps
- Largest number of distinct moth species from a single trap: 711 at Rhandirmwyn, Wales
- The longest serving volunteer Ian Tillotson has clocked up 46 years of light-trap operation
Tags: crops national capabilities Rothamsted Research video feature