Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
8/26/02
Contacts:
Betsy Matos, Entomology, (515) 294-1999, bmatos@iastate.edu
Jean McGuire, Continuing Education and Communication Services, (515) 294-7033,
jmcguire@iastate.edu
Yard and Garden Column for the Week Beginning Aug. 30, 2002
Invite Some Predators into Your Garden
By Betsy Matos
Entomology Research Assistant
Iowa State University Extension
Predators. Just the word invokes images of cold-blooded killers that strike without warning and prey on small, defenseless animals. Popular images aside, predators, those animals that attack and feed on other animals, are important links in food chains and in the environment. Imagine a world without predators. Rabbits would rule and our garden plants would be nonexistent.
Insect predators are larger and stronger than their prey and their survival and longevity are dependent on the availability of prey. Common insect predators in the Iowa landscape include green lacewings, lady beetles, praying mantids and ground beetles. Less well known are the microscopic arthropod predators.
It has been said that good perfumes and deadly poisons come in small packages. This is also true about some very small but important creatures found in our lawns, gardens and greenhouses: mites. Some mites (spider mites) are harmful to plants. Others, however, are predators and are beneficial. These beneficial predators provide a valuable and free service by helping keep damaging insect, including spider mite, populations low.
Mites are often thought to be insects, but they are more closely related to and resemble spiders. Mites have eight legs, bodies that are divided into two main regions and lack wings and antennae. The nymphal stage is very similar to the adult stage except nymphs are smaller. Both nymphs and adults are predators. Predatory mites are very important biological control agents that most of us miss while admiring a beautiful garden. Even though they are smaller than the head of a pin, their magnitude in the garden is comparable with the importance of soil in a vegetable garden.
An interesting characteristic that distinguishes predatory mites from pest mites is that predatory mites can walk both forward and backward and pest mites only walk forward. Because predatory mites are blind they find their prey by using chemicals given off by the plants on which prey feed. In addition to eating spider mites, predatory mites feed on thrips and aphids in greenhouse and gardens. Thrips are small pests usually found in flowers.
An attractive aspect of predatory mites is that they are mass-produced in the United States. Predatory mites are used in commercial greenhouses and other controlled environments. Once released in the designated area they do not move far away. Thus, the use of pesticides can be detrimental to their development.
It is generally not practical to purchase and release predatory mites in the home garden or landscape. Instead, you can conserve predators, including mites, by following environmentally friendly pest management practices in the garden:
* Promote biodiversity in the landscape
* Be tolerant of pests and leave a reservoir of food for biological controls
* Use nonchemical pesticides such as insecticidal soap, horticultural oil and microbial insecticides when practical.
(A picture of a predator mite can be found at the following Web site: http://floriculture.osu.edu/archive/apr99/premite1.html.
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