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United States Department of Agriculture

Agricultural Research Service

Weevil Text

Eat Yourself Sick!
These roots put the "die" in "diet."

Have you ever eaten something that made you feel sick?

People respond to food differently, and sometimes our bodies respond to food in a bad way. Kids with lactose intolerance, peanut allergies or diabetes can have a bad reaction to food that's made with dairy, peanuts or too much sugar.

And all kids would have a bad reaction to food that's spoiled or undercooked. Bleh!

The world is full of living creatures, and each kind has a special diet.

For every animal, there are foods that will help it grow healthy and strong––and others that will make it as sick as spoiled food would make you or me.

Knowing which foods an animal can and cannot eat lets us take good care of our pets and agricultural animals.

And it also helps us get rid of pests––such as weevils.

A weevil is a tiny beetle that eats plants, and it's a major pest! Americans have to spend a lot of money to keep their plants safe so weevils won't eat them.

Often that means spraying the plants or the soil with something to keep the weevils away––or to kill them.

Different kinds of weevils eat different kinds of things. For example, young black vine weevils (called larvae) enjoy eating roots––which is a big problem in nurseries.

Some insects are picky eaters, but black vine weevils will eat the roots of lots of different nursery crops. They especially like yew, hemlock and rhododendron. They'll also eat begonia, lilac, peony and strawberry plants.

Adult black vine weevils prefer to eat leaves, and they leave ugly marks on the plants. But the larvae are even worse.

Larvae of black vine weevils and other root-eating insects eat the roots of important nursery plants, and the plants die before nurseries can sell them to gardeners.

One way to protect plants is to use fungi that cause diseases in insects. Fungi are simple organisms, like mushrooms and toadstools, that get their nutrients from the environment around them instead of making their own nutrients through photosynthesis.

Sometimes they're edible. For example, humans eat mushrooms in soups, omelets, pizzas and salads. But other mushrooms are really dangerous to eat.

Different kinds of fungi can be dangerous for insects too, and the insects don't even have to eat them to get sick. If the fungal spores (tiny cells that help the fungus reproduce) contact the insects' cuticles (their exteriors, sort of like our skin) they can enter the insects and make them really sick.

Fungi that kill insects are called entomopathogenic [EN-toe-mo-path-oh-JEN-ic], which is basically a fancy word for "insect-killing." Sometimes weevils like to eat things that are bad for them, and that's a trick that scientists can use to keep them from damaging plants.

Denny Bruck is an entomologist (a scientist who studies insects) in the Agricultural Research Service's Horticultural Crops Research Unit at Corvallis, Oregon. He found an entomopathogenic fungus that is very bad for weevils. In fact, it can kill them. Using this substance could help us protect our plants from weevils.

Why would a weevil eat a fungus if it's unhealthy? The answer is that they don't. They'll eat something that's good for them––like roots––that brings them close to the fungal spores. Then the spores penetrate their cuticles and cause an infection. They think they're eating something tasty and nutritious, but it's actually bringing them into contact with something dangerous.

Imagine a prank where somebody leaves a piece of cake in the middle of a huge poison ivy patch. If the school bullies try to steal the cake, they'll get an itchy case of poison ivy! Bruck's solution works the same way. He lures the weevils in with one of their favorite foods. When they come to eat it, they run into the deadly spores, with gross results.

Bruck found that the best way to get insects in contact with these dangerous fungi is to make a liquid solution with fungal spores (which are very, very tiny) and dip the plant roots in it.

Then when the insects go for a mouthful of delicious roots, they get close to the spores. In fact, Bruck found that these fungi grow very well near plant roots, so there are plenty of spores around to infect the insects.

Even better, these black vine weevils actually prefer the plant roots that have the fungus on them, which means they are more likely to snack on the roots that will harm them.

This is bad news for the weevils, which will––literally––eat themselves sick. But it's great news for scientists, nurseries, gardeners and anyone who appreciates beautiful, healthy plants.

—By Laura McGinnis, Agricultural Research Service

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Last Modified: 10/9/2007
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