For decades, the farmers of East Africa have battled the African whitefly, a tiny insect that infests the cassava crop. Cassava, also called manioc, arrowroot or tapioca, is an important food all over the world — more than half a billion people (yes, billion with a b) rely on cassava for their daily meals. For East African farmers, a whitefly infestation can completely destroy the year’s crop, and with it the food security for their families.
Yet surprisingly little is known about the whitefly itself. It’s only in the past few years, in fact, that scientists even knew whether there was more than one species — and now, it turns out, there are at least 34. Who’s counting? Computational biologist Laura Boykin, who studies the Bemisia tabaci whiteflies that plague East Africa, using genomics, supercomputing and evolutionary history. With the data she’s gathering, now publicly available via WhiteFlyBase , she hopes to help researchers breed new strains of cassava that resist the whitefly.
We asked Boykin to tell us more about her work, how she discovered this problem … and how she realized she had the right skills to help solve it.
Tell us about the whitefly and cassava. Why is this problem crucial to solve?
700 million people around the world depend on cassava for their daily calories. Without it, for many families, there’s no food and there’s no income. To understand the importance of cassava in a farmer’s life, read The Last Hunger Season, by Roger Thurow. Depending on the country, farmers typically have a one-acre plot, which might include beans and other crops. In Kenya, for example, they’ll grow maize and sweet potatoes, and cassava is a backup. It’s planted and takes a while to grow, so when all the other crops are gone, the family thinks, “Okay, the cassava will get us through the hunger season.” But if it’s rotten due to whitefly, there’s absolutely no food.
Whiteflies transmit two viruses that kill cassava: cassava mosaic disease and cassava brown streak disease. In tandem, these cause 100 percent loss of the crop. It’s a massive problem, especially in East Africa. I’m one of 15 principal investigators working on a new project whose mission is to give farmers a cassava plant that’s resistant to the viruses and the whiteflies. How do we get there? Whiteflies are a global problem, creating havoc on every continent. So first, it’s identifying what whiteflies and viruses are present in East Africa.
Where did the problem originate?
Cassava originates from South America, and was taken to Africa in the 1700s. But these viruses aren’t found in South America. The hypothesis is that they’d been lying dormant in African native vegetation. We think that the whiteflies feed on native shrubs, then go feed on cassava, transmitting the virus from the shrubs to the cassava plants.
Fortunately, the viruses haven’t yet spread to West Africa, the biggest cassava-producing place in the world. Right now, the virus is concentrated in a pocket of East Africa: Tanzania, Uganda, Malawi, Mozambique and Zimbabwe. The hope is that we can control the whiteflies enough so that they don’t spread.
When did whitefly infestation start becoming a noticeable problem?
In the 1990s, researchers were attempting to control cassava mosaic disease that was breaking out in East Africa. They thought they had a control for it via traditional breeding. Then the cassava brown streak virus emerged; it turned out that whiteflies loved the new varieties that the researchers rolled out to control the first virus. In essence, the researchers had been trying to breed for virus resistance without taking into account that there might be different species of whiteflies.
We’ve done modeling based on genetic data indicating that Africa is the origin of the species, so it makes sense there will be the most diversity there. With that information, we are working to ensure that the people who are doing the plant breeding get the resistance right for all the whitefly species that the plant might encounter.
How did scientists not know that there was more than one species of whitefly?
This is the interesting part. The idea that there was only one species of whitefly worldwide was held for so long and became so ingrained that no one seems to care what the data says now. Meanwhile, the funding to do work on whiteflies — especially in sub-Saharan Africa — has been so scarce that no one was able to even look to see what’s there. It’s only been in the last seven years or so that people have started to do sampling of the region. The more we sample, the more we realize there are tons more species of whitefly in Africa than we ever thought.
One of the difficult things about identifying new species is that scientists are under pressure to not change their names, because then all the names within the governmental regulations have to be changed. There’s also pressure from chemical companies, who market their products for specific species. If we say there are 34 species — and not one — they have to test their products on all 34. We are creating more work for people, and there’s enormous resistance. But the science is the science. We need our solutions customized to the right enemy. It’s a non-negotiable point.
By the way, the whitefly is highly regulated around the world. Countries have massive regulations on whitefly moving across borders. It can transmit viruses to tomatoes, sweet potatoes and ornamental plants. They are dreaded worldwide.
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