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University of Minnesota Extension

Identifying good bugs and bad bugs in your yard and garden

This is the time of year that bugs enter the picture.  Bugs in jars line my desk and the freezer in the office, and the main question I get is “how do I get rid of it?!?” The answer is not always simple, because as much as I can understand a squeamishness about these creepy crawlies, some of them are good guys, doing productive work in your garden; and some of them are bad guys, having detrimental impact to your garden.  (Some of them are negligible, neither good nor bad.) How do you know when to act and when to let nature take its course? Let’s look at some of these critters and the work or damage they do.

There are two types of bugs that are good in your garden: predators and parasitoids.  Predators feed on and kill bad bugs; their larvae are often voracious eaters. Parasitoids are smaller than the hosts on which they feed. They act as parasites, laying their eggs on, in or near bad bugs. The eggs hatch, and the larvae feed on the bad bugs, sometimes eating them from the inside out! Predators include the Green Lacewings (Chrysopidae),which eat many pests including aphids, scale insects, caterpillars and white flies; Aphid Midges (Aphidoletes), which paralyzes and kills aphids with toxic saliva, then eats them; Ladybugs (Coccinellidae), which eat mites, mealy bugs and aphids;  and Minute Pirate bugs (Anthocoridae), which devour just about any insect pest.  Parasitoids are either small wasps or flies, which are often too tiny to see. They live and feed on or in the tissue of a pest, parasitizing and eventually killing the host.

These bugs are good to have around! One ladybug can eat as many as 5000 aphids during its lifetime. Green lacewings are known as Aphid Lions; each green lacewing larvae can eat 200+ pests per week.

There are also many bugs which do harm to your garden.  Some of the most damaging are: Tomato Hornworms (Manduca quinquemaculata), which quickly defoliate and destroy plants in the tomato family; Japanese beetles (Popillia Japonica), which devour just about every plant in its path; Colorado Potato Beetles (Leptinotarsa decemlineata), which destroy plants in the potato family; and Stink bugs (Pentatominae), which releases a foul odor when disturbed and feed on fruit and vegetable plants. These pests can do significant damage to your garden, and are best controlled through cultural and chemical measures.

The most important factor in pest control in your garden is proper identification. You have to know what pest you’re dealing with before you can create a plan for its removal.  To help you figure out what’s eating your plants, visit “What Insect is this?” at: www.extension.umn.edu/garden/diagnose/insect/. This interactive tool will help you identify some of the most common insects found in Minnesota gardens, and make recommendations for their control. If you are still having trouble identifying your insect invader, put it in a sealed container and bring it to the Extension office, I can take a look and help you determine what insect you have, and the best way to take care of it.

Remember, not all insects are bad.   Take dragonflies, they can eat 30 to 100s of mosquitos a day.  When you see a swarm of dragonflies darting around on a warm summer’s evening, just think of the work they are doing to make you more comfortable outside!  Gotta love those bugs!

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