How Do Lady Beetle Releases Affect Aphid Populations in Gardens?

Lady beetles are often offered for sale for controlling aphids in home gardens. But are they of any benefit?

Select several plants (or branches of a tree) that have aphids on them for your test plants. Mark eight or twelve branches with tags so you easily locate them. Count or estimate the number of aphids on the branch, and record this information for each branch. Enclose half of the branches in cages and leave the rest exposed. (You can make simple cages with mosquito netting or other finely woven fabric. Cut out a square piece of netting and fold it in half. Sew the long side and the bottom shut. Insert your aphid-infested branch into this "sleeve cage" and tie the open end closed with a piece of string.) Be sure to remove any natural enemies that might be on the branches before putting on the cages. Release about 5 lady beetles (purchased or collect them yourself) on half of the exposed branches and into half of the cages. The remaining exposed and caged branches will be your controls.

Inspect the branches for lady beetles and count the number of aphids on the branches again in 3 days, and/or a week, and/or two weeks. How have the aphid populations changed? Were any lady beetles still on the exposed branches? If not, where do you suppose they went? Do you think the exposed aphids were eaten by the lady beetles you released, or were they destroyed by other naturally occurring biological control agents? Or did they increase in number? What about the aphids in the cages? Did they increase in the absence of lady beetles? Did caging the lady beetles to keep them from flying away improve aphid control? Do you think it would be worth the cost to buy lady beetles to release in your garden?

- Susan Mahr, University of Wisconsin - Madison


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