Worms, Lambs and Sweet Corn
1Seun Bramwell, an eighth grader, lives on his family's farm in a valley of rolling pasture. The family keeps about 120 ewes, female sheep that each raise one or two lambs a year, and grows sweet corn for a roadside farm stand. Two pests cause most of their trouble. The first is a small blood-feeding worm that lives in a sheep's stomach. Lambs swallow young worms with the grass they eat, and a heavy infection can make a lamb weak and pale or even kill it. The second is the corn earworm, a caterpillar that chews into the tip of a sweet corn ear. Customers seldom buy a damaged ear.
2Over the years, the dewormer medicines the farm uses have killed fewer and fewer of its worms. The family's veterinarian, Dr. Marguerite Szabo, suggested breeding the flock to carry fewer worms. She showed Seun how to do an egg count. A little dung from a lamb is mixed with salt water so the worm eggs float, and the eggs are counted under a microscope on a counting slide. The result is given in eggs per gram of dung, and a higher count usually means more worms. Lambs grazing the same pasture can carry very different numbers of worms and still look about equally healthy.
3Since 2016, the farm has counted every lamb at weaning, with no dewormer in the six weeks before. The family keeps the female lambs with the lowest counts as future mothers and sells the rest for meat, and it buys rams whose lambs on other farms had low counts. Each dose of dewormer kills mostly the worms the medicine still works on, so the more doses a farm gives, the faster worms that survive it take over. Across the road, the Ferreira farm grazes similar pasture and counts its lambs the same way, but it chooses parents only for their size. In 2024 the Bramwells also borrowed Ram B from a farm that had never counted its lambs.
4Seun's mother, Mrs. Abimbola Bramwell, tried a new kind of sweet corn this year. To make it, scientists put a gene from a soil bacterium called Bt into corn cells in a lab and grew whole plants from those cells. The gene carries instructions for a protein that harms certain caterpillars that eat the plant. Sweet corn does not make this protein on its own. Many years of tests have not found the protein to harm people, pets or honeybees. Last year, the farm sprayed its regular sweet corn with insecticide 6 times to protect the ears.
5For her test, Mrs. Bramwell planted 4 strips of the Bt corn and 4 strips of the regular version of the same variety, side by side. All 8 strips were planted on the same day and got the same water and fertilizer, and none were sprayed. At harvest, she checked 100 ears from each strip for earworm damage.