Science: Flower extract that promises lingering death: Researchers have a new weapon against malaria-carrying mosquitoes. Now they are developing pesticides from the same plant sources. David Spark reports

RESEARCHERS at Rothamsted Experimental Station, Hertfordshire, are scanning the plant world for a successor to one of their greatest finds, the pyrethroid insecticides. One new compound has already been patented.

A pyrethroid called lambda-cyhalothrin, produced by ICI under the trade name Icon, is a new weapon for curbing the growing threat of malaria in Africa and other areas where malaria parasites are resistant to drugs. It shares with other pyrethroids the advantage that, unlike DDT, it degrades swiftly in contact with the soil and so leaves no harmful residues. But it will linger to kill mosquitoes for six months on an inert surface such as a house wall.

Research in Tanzania and South Africa has shown it to be 10 times more effective than DDT for killing malaria-carrying mosquitoes in houses, according to Dr Graham White of ICI Public Health. Unlike DDT, it does not repel mosquitoes and allow them to escape. In one Tanzanian village, it greatly reduced malaria among newborn babies. It is the first insecticide to win World Health Organisation approval for malaria control since the WHO revised its evaluation scheme in 1982.

Countries in impoverished Africa have little money for spraying. But 16 countries worldwide have bought the new insecticide. One is Zimbabwe, and Dr White calculates that taking into account the low transport and handling costs for the small quantities needed, Icon is as cheap to use in that country as any mosquito killer.

The pyrethroid success was based on compounds extracted from the pyrethrum flower which kill insects but break down rapidly in sunlight. Sixteen years ago, Dr Michael Elliott and colleagues at Rothamsted discovered more stable and active pyrethroids suitable for more uses, especially in farming. These compounds have little impact on the environment. A new generation of non-ester pyrethroids - simpler molecules than the old - is being developed.

After the pyrethroids came the highly active avermectins, microbial products discovered in the United States and Japan. Their toxicity towards mammals makes them unsuitable for arable use, but they have a role in veterinary medicine.

Now research is returning to plants, which synthesise a wide range of compounds to protect themselves against their enemies. The normal approach to screening compounds is to check hundreds a week by a rapid technique such as spraying leaves and putting insects on them. Anything highly active produces a clear-cut answer, but a compound present in only minute quantities may be missed.

The Rothamsted team prepares extracts with three solvents, each dissolving a different range of compounds. This makes the effectiveness of any particular compound easier to spot. 'We consider plants a valuable resource,' Dr Bhupinder Khambay, the leader of the research group, says. 'We look at each species carefully.'

They rear insects methodically, including insecticide-resistant strains. The extracts are applied to individual insects: 'This is labour-intensive,' Dr Khambay says, 'but the test is more sensitive and the results are more accurate.'

In discovering the pyrethroids, Rothamsted used only two test species: susceptible houseflies and mustard beetles, but now it also uses mites, whitefly, the cornroot worm and the diamond-backed moth (scourge of cabbages in the tropics). 'We are on the lookout for selective compounds as well as broad-spectrum ones,' Dr Khambay says.

Dr Khambay began his current work with plants supplied by Biotics Ltd, based at Sussex University. Professor Bob Thomas set up Biotics as a bridge between plant-supplying tropical countries and the organisations that can screen plant compounds for useful properties as drugs or pesticides.

This has the advantage that royalty payments for the use of a successful compound can go back via Biotics to the country of origin. The source country can also benefit by cultivating the successful plant to produce a cheaper, local source of pesticides. Dr Khambay says: 'We have direct links in several countries, with similar arrangements.'

He points out that, apart from income from commercial successes, developing countries can gain valuable practical experience of work in Rothamsted's well-equipped laboratories.

This is the first of three articles on modern advances in pesticides.

Start your day with The Independent, sign up for daily news emails
Arts and Entertainment
Brendan O'Carroll as Agnes Brown in the 2014 Mrs Brown's Boys Christmas special
tvCould Mrs Brown's Boys have taken lead for second year?
Arts and Entertainment
Jack O'Connell stars as Louis Zamperini in Angelina Jolie's Unbroken
film review... even if Jack O'Connell is excellent
News
news
News
peopleIt seems you can't silence Katie Hopkins, even on Christmas Day...
PROMOTED VIDEO
Arts and Entertainment
Wolf (Nathan McMullen), Ian (Dan Starky), The Doctor (Peter Capaldi), Clara (Jenna Coleman), Santa Claus (Nick Frost) in the Doctor Who Christmas Special (BBC/Photographer: David Venni)
tvOur review of the Doctor Who Christmas Special
Life and Style
fashion
Arts and Entertainment
Japanese artist Megumi Igarashi showing a small mascot shaped like a vagina
art
ebooks
ebooksA year of political gossip, levity and intrigue from the sharpest pen in Westminster
News
i100
Arts and Entertainment
Left to right: Stanley Tucci, Sophie Grabol and Christopher Eccleston in ‘Fortitude’
tvSo Sky Atlantic arrived in Iceland to film their new and supposedly snow-bound series 'Fortitude'...
Arts and Entertainment
tvChristmas special reviewed
Arts and Entertainment
Jenna Coleman as Clara Oswald in the Doctor Who Christmas special
tvForget the rumours that Clara Oswald would be quitting the Tardis
Arts and Entertainment
tv
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating
and  

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

Ashdown Group: Senior Marketing Executive- City of London, Old Street

£40000 - £43000 per annum + benefits: Ashdown Group: Senior Marketing Executiv...

Ashdown Group: Marketing Manager

£40000 - £43000 per annum + benefits: Ashdown Group: An international organisa...

Ashdown Group: Internal Recruiter -Rugby, Warwickshire

£25000 - £30000 per annum: Ashdown Group: Internal Recruiter -Rugby, Warwicksh...

Ashdown Group: Marketing Manager/Marketing Controller (Financial Services)

£70000 - £75000 per annum + benefits: Ashdown Group: Marketing Manager/Marketi...

Day In a Page

A Christmas without hope: Fears grow in Gaza that the conflict with Israel will soon reignite

Christmas without hope

Gaza fears grow that conflict with Israel will soon reignite
After 150 years, you can finally visit the grisliest museum in the country

The 'Black Museum'

After 150 years, you can finally visit Britain's grisliest museum
No ho-ho-hos with Nick Frost's badass Santa

No ho-ho-hos with Nick Frost's badass Santa

Doctor Who Christmas Special TV review
Chilly Christmas: Swimmers take festive dip for charity

Chilly Christmas

Swimmers dive into freezing British waters for charity
Veterans' hostel 'overwhelmed by kindness' for festive dinner

Homeless Veterans appeal

In 2010, Sgt Gary Jamieson stepped on an IED in Afghanistan and lost his legs and an arm. He reveals what, and who, helped him to make a remarkable recovery
Isis in Iraq: Yazidi girls killing themselves to escape rape and imprisonment by militants

'Jilan killed herself in the bathroom. She cut her wrists and hanged herself'

Yazidi girls killing themselves to escape rape and imprisonment
Ed Balls interview: 'If I think about the deficit when I'm playing the piano, it all goes wrong'

Ed Balls interview

'If I think about the deficit when I'm playing the piano, it all goes wrong'
He's behind you, dude!

US stars in UK panto

From David Hasselhoff to Jerry Hall
Grace Dent's Christmas Quiz: What are you – a festive curmudgeon or top of the tree?

Grace Dent's Christmas Quiz

What are you – a festive curmudgeon or top of the tree?
Nasa planning to build cloud cities in airships above Venus

Nasa planning to build cloud cities in airships above Venus

Planet’s surface is inhospitable to humans but 30 miles above it is almost perfect
Surrounded by high-rise flats is a little house filled with Lebanon’s history - clocks, rifles, frogmen’s uniforms and colonial helmets

Clocks, rifles, swords, frogmen’s uniforms

Surrounded by high-rise flats is a little house filled with Lebanon’s history
Return to Gaza: Four months on, the wounds left by Israel's bombardment have not yet healed

Four months after the bombardment, Gaza’s wounds are yet to heal

Kim Sengupta is reunited with a man whose plight mirrors the suffering of the Palestinian people
Gastric surgery: Is it really the answer to the UK's obesity epidemic?

Is gastric surgery really the answer to the UK's obesity epidemic?

Critics argue that it’s crazy to operate on healthy people just to stop them eating
Homeless Veterans appeal: Christmas charity auction Part 2 - now LIVE

Homeless Veterans appeal: Christmas charity auction

Bid on original art, or trips of a lifetime to Africa or the 'Corrie' set, and help Homeless Veterans
Pantomime rings the changes to welcome autistic theatre-goers

Autism-friendly theatre

Pantomime leads the pack in quest to welcome all