WHEN IS A BUG NOT A PEST?

by Glenn Davis, UCCE Master Gardener, El Dorado County

April, 2003

Each year in the spring, when we start our serious weeding, we run across a variety of bugs in the weeds and on our plants. My wife occasionally captures the little critters and wants to know if they are good bugs or bad bugs. There are such a variety of critters it is often not easy to tell since both good and bad bugs sometimes look like each other.

There are parasitic bugs that use another bug as a host for developing eggs and there are predaceous bugs that eat other bugs. There are also some bugs that secrete materials that repel other bugs and on occasion the competition for food is so great it kills off bugs. To try and explain the entire bug world would require a textbook, not a newspaper article.

There are a host of critters out there that we casually call bugs; a better name would be “insects.” Generally we know insects as those six-legged critters with antennae, a head, thorax (chest), and abdomen. They are invertebrates, have an exoskeleton and while some have wings and wing covers there are some who are wingless. These are only part of the group of pests that can invade your garden; luckily they are the easiest to identify. If you want to get serious about bug identification it would help if you had a hand lens.

To give you a little more to work with let us limit the discussion to two different insect orders “True Bugs, Hoppers, Aphids and Scales” and “Beetles.” There are a lot of other orders out there, ants, butterflies, lice, grasshoppers and termites, but these two orders seem to have a lot of easily identified culprits.

Gardens are mixtures of plants and the best method for controlling any insect population is diversity. A single predominant crop will encourage the reproduction of a single pest; with a diversity of plants you get a diversity of insects and they tend to control one another. Your basic job is to be able to identify and monitor those you find and know when they have reached a dangerous stage in the garden.

True bugs have mouths that have a needle like tube that is hollow for piercing and sucking and their double wings form an “X” on their back.

Beetles on the other hand have mouth parts, not a tube, and their wings form a straight line down their back. Both can be very small or quite large depending on the family.

The good true bugs are, remember these are the bugs with the “X” on their back, pirate bugs, damsel bugs, assassin bugs, stink bugs bigeyed bugs and ambush bugs. These are terrestrial and can be found in most of our gardens.

The good beetles, with the wing line straight down their back, are the ladybird beetle, rove beetle, checkered beetle, ground beetle, soldier beetle, and two aquatic beetles, the whirligig and diving beetles.

With the exception of the ladybird and whirligig beetle most gardeners would not be able to identify any of the insects listed above. These are all good guys and if they are in your garden they will frequently use other insects as a food source and hopefully keep them down to a manageable number. Keep in mind if you use a chemical spray to control insects you may very well kill off some of these good pests.

To better identify insects in your garden I would recommend you refer to a couple of books, California Insects, Powell and Hogue, which can be purchased at your local bookstore and Natural Enemies Handbook, The Illustrated Guide to Biological Pest Control, publication 3386, which can be purchased at the El Dorado County Farm Advisor’s office, 311 Fairlane, Placerville, CA.