Saturday, September 13, 2008

How to Attract Beneficial Insects

Possibly you will look at this title and say you don't care how to attract beneficial insects and you don't want to! But the term beneficial says it all. You need insects in your garden if you are going to have the best possible garden. There are statistics that say that there are many more beneficial than destructive insects. To name a few destructive insects: there are flies (but they are also pollinators); there are mosquitoes (also pollinators); there are cockroaches (but they eat garbage and scavenge); there are termites (maybe these insects are strictly destructive). Now that we have gotten the bad bugs out of the way we can concentrate on bugs that are good in so many ways.

For a good while the term beneficial insect (or natural enemy of other bugs) has meant that the good bugs attack and eat the bad bugs. Some bad garden insects include the ever-present and always plentiful aphid; many vegetable garden pests such as Colorado potato beetle, Harlequin bug, green cabbage worm, tomato hornworm, flea beetles, corn ear worm, and many other caterpillars are also considered bad-especially

Caption is Ladybug larva--usually described as looking like a small alligator. It is the stage that eats most of the aphids.

by gardeners. And, of course, Japanese beetles are the bane of the gardener's life. Every one of these pests is eaten or parasitized by lady bugs, green lacewings, bees, wasps, and flower flies. The ladybug is probably considered the poster child of good insects and its larva can eat between 30 and 40 aphids a day, while a single lacewing devours between 1,000 and 10,000 aphids in its lifetime. Insert picture of ladybug larva in this paragraph. (Caption is Ladybug larva--usually described as looking like a small alligator. It is the stage that eats most of the aphids.

I hope you won't put bees in the bad category. We desperately need honey bees, bumblebees, and solitary bees to pollinate our plants. If you are stung, it's most likely that you will be stung by a yellow jacket and that happens most often in the late summer or fall when these insects are seeking sugar and scavenging in our picnic food. Keep in mind proper behavior when you are around yellow jackets. Don't panic and run or wave your arms around. Stay calm and move slowly away from the wasp. Avoid wearing strong scents and bright-colored clothing. Yellow jackets live in the ground so this is often a source of the attack because you have disturbed the nest.

Attracting beneficial insects depends on you planting flowers and other plants that attract the insects. Some insects are very small (tiny wasps that don't sting humans) and so they like tiny flowers such as alyssum, or those in the mint family, or many herbs. Of course to attract the insect you must allow the plant to form flowers. If you are growing herbs, you may be picking off the basil flowers as they appear or the parsley flower when it appears. All flowers of the flat type consisting of many tiny flowers (parsley, dill, fennel, Queen Anne's lace, sunflowers, and yarrow) are very attractive to bees and flower flies and wasps. The beneficial insects that arrive will eat up the pests first and then stick around to eat pollen and nectar from your flowers.

Note the speckles on the foxglove flower that lead a bee to the interior for nectar and pollen.

Other flowers that attract bees especially are tubular flowers such as foxglove. If you look carefully at a foxglove flower you can picture the lip of the flower as a landing pad for the insect and the speckles and spots that are in many foxgloves will lead the bee into the flower for the nectar. Insects don't see color the same as we do: bees cannot see red flowers but they are attracted to blue and yellow flowers. Hummingbirds, with their sharp, pointed beaks, are also attracted to tubular flowers and they do like the color red. Most hummingbird feeders include parts that are red.

Include a mixture of plants in your garden that bloom at different times of the year. In the early spring when witch hazel shrubs and early crocus are blooming, you will usually find some bees that come out of hibernation early and get busy pollinating. Other plants that provide food for insects in early spring are Cornus mas (Cornelian cherry), Winter aconite (a bulb), and Oregon grape. At the end of the season, provide Michaelmas daisy, purple coneflower and goldenrod to serve the bees and other insects before they hibernate or die. Include in your plantings small trees and shrubs to provide songbirds with cover, food, and nesting sites. Choose a berry-producing shrub, perennials left to go to seed, and fruiting vines with berries or fruit that will persist throughout the winter. Some examples might be Ilex verticillata ('Winter Red' winterberry-buy a male and a female plant for more berries), 'Donald Wyman' crabapple, Staghorn sumac, and Viburnum trilobatum (American cranberrybush-you should have more than one viburnum to encourage flowers and fruit).

If you have room plant a patch of native wildflowers in or near your garden; this will attract native beneficials that will use them for shelter and food. And plant as many native plants as you can since they are adapted to the area and in general will grow better than some exotic plants.

Another thing you can do to make your garden attractive to insects is to provide water and shelter. Using a thick layer of mulch (2 to 3 inches) will attract ground beetles, spiders (they are good for your garden!) and toads. All are considered beneficial to your garden; they all devour many insects. The side benefit of mulch is that it cuts down on weeds and conserves water in the soil.

Flowers that are not attractive to insects include double or very full-petaled flowers-the insects can't find the pollen or nectar. These flowers would include double hollyhocks, double petunias, and many hybrids such as pollenless sunflowers. Getting rid of the pollen in a flower benefits the human who cuts flowers for bouquets, but the flower is useless to insects.

Butterflies and moths are considered beneficial, in addition to being beautiful. They don't actually eat when they are in this adult stage, but they do sip nectar and in the process help to pollinate flowers. Moths are most often active at night and this is why so many white or pale flowers bloom at night and have a scent that is attractive to moths. Think of moonflowers or four o'clocks that actually do start to bloom in the late afternoon. There are hawk moths that fly at night and are attracted to nicotiana, moonflowers, cleome, and petunias. Do you ever notice the scent of a petunia at dusk on a hot summer evening? So does the moth.

Butterflies are active in the daytime and actually only fly when it is warm and sunny enough to suit them. You will not see them flying around on cloudy days and certainly not when it is raining.

The juvenile stage of the butterfly and the moth is the caterpillar that makes the cocoon or pupa from which the butterfly or moth emerges. Most caterpillars are considered pests and people do their best to eliminate them. The green cabbage worm turns into that ubiquitous white moth that flutters on cabbage and broccoli plants, the tomato hornworm or tobacco hornworm turns into a large attractive moth. So even though you don't like the worms or caterpillars you should let some complete their life

Parasitized tobacco hornworm on tomato plant with braconid wasp cocoons along back of caterpillar

cycle and turn into the beautiful butterfly. Here is another reason not to kill the tomato hornworm. There are tiny wasps that lay their eggs on the caterpillar and the eggs grow and finally hatch from the parasitized worm that doesn't die until the eggs have hatched into new little wasps.

It is obvious that you shouldn't use chemicals if you want to attract beneficial insects. The chemical can't tell the difference between good and bad bugs-you are most likely to kill all the insects. Even if you follow the directions carefully, there will be at least some good insects that will be killed. When insects do return to your garden, you may have destroyed the balance between good and bad and the bad insects will take over. If you feel that you have too many aphids and you don't see any ladybug larvae, you can always shoot a hard stream of water on the aphids and knock them to the ground. They will not be able to climb back up to the tender tip of a stem. Or try an insecticidal soap on appropriate plants and insects. To get rid of caterpillars, pick them off and try to control their numbers by attracting birds to your garden. Slugs and snails can be discouraged with crushed eggshells, cut hair, sharp grit and oatmeal sprinkled on the soil.

And most important of all, spend time in your garden every day to monitor the insect life and the health of your plants. No one can get rid of every bad insect so learn to live with an insect population that is kept in check by the good guys

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