Sweep Net Samples in Alfalfa to Show Natural Enemy Diversity

Alfalfa fields are rarely sprayed with insecticides, so they contain a wide variety of pest and beneficial insects. Take a closer look at what's there by capturing some of the insects with a sweep net.

Take 10 to 50 sweeps with a standard sweep net. (If you have a chance, do some sampling before the actual demonstration. You'll be more familiar with what's in the field, and you'll have a better idea of how many sweeps to take per sample to ensure having enough insects, but not too many, per netful.) You may wish to do the sweeping yourself, or let members of the group take their own samples after you show them how.

Dump out the contents of the net into a shallow pan or clear plastic box. Insects that can fly may leave the pan, but those in the box can be restrained by covering the opening with a black cloth.

What do you see? Try to identify the beneficials a reference book with photos could be helpful, especially if you're not familiar with these insects. You're likely to see green lacewing larvae and adults, minute pirate bugs, lady beetle larvae and adults, damsel bugs, small stingless wasps of various sorts, spiders, and a wide variety of other critters. Which ones are most common? What do these beneficials eat? If you're lucky you may see one of the predators actually feeding on another insect!

- Susan Mahr, University of Wisconsin-Madison


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