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United States Department of Agriculture

Agricultural Research Service

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Ever wonder what spiders and bugs eat?

There's an easy way to find out: mash them up and see what's inside.

It's called a bug gut analysis. Scientists use it to keep pest populations under control. A pest is an insect that bothers other plants or animals. If there are too many of them, they can cause a lot of problems.

James Hagler and Steven Naranjo are entomologists (en-toe-MALL-o-jists) with the Agricultural Research Service (ARS). An entomologist is a scientist who studies bugs. Hagler and Naranjo work with insects that eat cotton, like whiteflies.


Adult and baby whiteflies (larvae) sit on a leaf.

Whiteflies like cotton a lot, but this is a big problem because they are pests. They can make a cotton plant sick by sucking up the sap in its veins or by giving it a virus. Or they can cover the plant with a liquid called "honeydew," which is sticky and gross. Plus, it's expensive to clean.

Ten years ago, there were lots of whiteflies in Arizona. The cotton farmers wanted to get rid of them. But how? One way is to find natural predators. A predator is an animal that eats other animals. But what kind of animal eats whiteflies? The farmers wanted to know, too.



Sometimes, being an entomologist is like being a detective. Hagler and Naranjo went to the cotton fields and collected insects and spiders to look for clues.



The entomologists crushed the specimens they had collected and put them on a special plate. Then they looked at what was inside their specimens' guts. Everything an insect (or spider) eats is in its guts. If it has eaten a whitefly recently, there will still be bits of whitefly in there. So the scientists added antibodies (AN-tee-BOD-eez). An antibody is a kind of protein.

These antibodies are like special magnets: they only stick to bits of protein from the whiteflies. If they bind together, there will be a color change. That means the bug is a whitefly predator.

By looking at insect guts, the scientists identified 18 whitefly predators. The cotton farmers were very happy.


James Hagler examines a plate to see if insect predators have been eating whiteflies.

A big-eyed bug devours whiteflies.






What happens next? When scientists identify a predator, farmers can use it to keep their farms safe. The predators will eat the whiteflies, and the cotton will be healthier.

Scientists can use this method for all sorts of insect pests—not just whiteflies.

This way, farmers can protect their crops without using lots of chemicals. It's cheaper for the farmers and healthier for everybody—except the pests, of course!


Click here to read a poem about Bug Gut Analysis!

By Laura McGinnis, Agricultural Research Service, Information Staff


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Last Modified: 8/12/2016
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