Pests and pestilence

Locust

Photoshot/VISUM/Still Pictures

Famine has many fathers. Sometimes it is caused by drought, sometimes by poor policies, sometimes by conflict, often by a combination of factors. And pests and diseases can be responsible too: though some victories are won, the battle against them continues.

Breeding resistance

Selective breeding is almost as old as agriculture, as farmers have sought to improve their crops and livestock, but breakthroughs in bio­technology have opened up previously unimag­ined possibilities. Recent developments include pota­toes that resist the blight that caused the Irish famine (see box) and maize bred with genes from two wild ancestors that help fight off seven major diseases and turn it into a perennial crop.

Whether by old methods or new, crops need to be refreshed with new genetic material – often from wild relatives – every 15 years or so because pests and diseases adapt to man-made countermeasures. The latest big threat comes from a new version of an old enemy. Stem rust, a disease caused by a fungus, has destroyed crops since earliest times, cut harvests in the United States of America by a fifth on several occasions between the world wars, and is so powerful it was developed as a biological weapon during the Cold War.

stem rust

Oregon State University

The last big US outbreak was in 1962, and by the 1970s victory seemed to be on its way as scientists had developed genetically resistant wheat. But recently it has returned with the evolution of a virulent new strain, Ug99 (Puccinia graminis). Since its discovery in Uganda 11 years ago, it has already spread to affect or threaten 29 countries in Africa, the Near East and Asia – which account for 37 per cent of global wheat production.

Scientists – who reckon that 90 per cent of all the world’s wheat varieties are vulnerable to Ug99 – have been working hard to cross resistant varieties with high-yielding local ones. But this takes time and the fungus is ever evolving to beat them. Just this summer, four new mutations able to over­come existing genetic resistance were discovered. The constant strug­gle under­­lines the importance of conserv­ing bio­diversity: old and wild varieties often hold the genetic raw material that can avert disaster.

Feeding frenzy

locusts

In its solitary form the desert locust is green; in crowded conditions it darkens to black and yellow. NASA

They sound biblical, but plagues of locusts are all too modern a scourge. Exodus describes how desert locusts (Schistocerca gregaria) ‘covered the face of the Earth so that the land was darkened and ate all the plants in the land so that nothing green was left’. And swarms – with 80 million of the insects in each of hundreds of square kilometres – still appear ‘out of nowhere’ to devastate crops. And even greater swarms have been recorded: a century or so ago a single flight over the Red Sea stretched over 13,000 square kilometres.

The weather signals their sudden appearances. Desert locusts – which are usually solitary – lay their eggs in dry sand, where they can stay for years until rain, at the right seasonal moment, causes them to hatch, breed rapidly and gather in such numbers that swarming behaviour is triggered. In 2004, the worst plague in 15 years swarmed across some 40,000 square kilometres of Mauritania, Mali, Niger and Senegal, devouring as it went.

On the other side of the world, un­usually heavy rains in central Australia recently led to high plant growth in the desert, allowing Australian plague locusts (Chortoicetes terminifera) to thrive. Swarming locusts have already consumed thousands of hectares of pasture and such crops as carrot, oat and canola, and Australia is bracing itself for a much larger outbreak later in coming months.

Individual locusts pose no threat to people and can even provide food: many eat them for protein. But when they appear in vast numbers people and animals go hungry. No wonder, when a swarm can contain billions of insects and eat tens of thousands of tonnes of vegetation in a single day. The Food and Agriculture Organization of the United Nations (FAO) coordinates efforts to contain the plagues through Locust Watch, which serves as a clearing­house of information on locust outbreaks and aids countermeasures, typically spray­ing pesticides from aircraft.

Fear of the fly

tetse fly

Wikimedia Commons

Small but deadly, the blood-sucking tsetse fly (Glossina) infests 37 African countries, covering nearly a third of the continent and threatening millions of people with sleeping sickness (African trypanosomiasis). The fatal disease is caused by single-celled parasites, trypanosomes, trans­mitted by the fly’s bite. Animals are also infected with the parasites, causing nagana, a similarly fatal disease.

Tsetse fly cuts agricultural productivity and increases food insecurity. It thrives in moist rural areas, so families are often forced to abandon good, fertile land to avoid it. The most recent outbreak began in 1970: by 2004, around 500,000 Africans had been infected. In 1997 the Government of Tanzania successfully eradicated the flies on Zanzibar by releasing sterilized males into the wild. But despite a campaign to eradicate it, sleeping sickness still affects some 50,000 to 70,000 people each year, while 60 million are at risk of infection.

Success!

Now here’s some good news. This year the FAO will officially declare that rinderpest, a highly contagious viral disease related to measles, has been eradicated. Cattle plague, as it is also called, is only the second disease, after smallpox, to have been driven to extinction.

In 1889, infected cattle shipped from India introduced the disease to Africa. It killed around 90 per cent of cattle in sub-Saharan Africa, along with many other domesticated and wild animals like wildebeest and giraffe; the resulting catastrophic famine killed two thirds of the Tanzanian Maasai and a third of Ethiopia’s people. And, until recently, it was still affecting countries as far flung as Brazil, Australia, Pakistan and the Philippines

The decline and fall of rinderpest

The decline and fall of rinderpest. Source: FAO

The breakthrough began with a vaccine developed by scientist Walter Plowright, who died earlier this year. The vaccine has been available since 1960, but only with the sustained global eradication campaign initiated by the FAO in 1994 has it been pos­sible to eliminate the disease.

GREAT FAMINES

Ireland 1846-1852

In 1846 Ireland had 8 million people. Over the next few years about 1 million died and 2 million were forced to emigrate after an imported fungus, potato blight (Phytophthora infestans), destroyed its potato crop, which provided 60 per cent of the nation’s food.

Great Chinese Famine 1959-1961

The worst famine in modern history arose not from natural disaster but from official policy. Chinese Chairman Mao Zedong’s ‘Great Leap Forward’ forced farmers to leave their fields when they were brought under collective ownership. Annual grain production declined from 200 million tonnes to 160 million tonnes in two years, and 10 to 40 million people starved.

Ethiopia 1984-1985

A million people died in 1984 when drought and disease destroyed crops in Ethiopia, leading to a 1-million-tonne shortfall in grain. The famine was made worse by civil war, slow delivery of aid from Western countries, and storms destroying new crops. Hundreds of thousands of refugees fled into Somalia, Djibouti and Sudan.

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This post is also available in: French, Spanish