|
|
| Mesoseiulus longipes has a brownish coloration. |
Mites are amongst the smallest of all members of the Animal Kingdom. Although they are incredibly abundant we rarely see them because most are under 1 mm (1/25th inch) long; some are much smaller than that. Mites comprise a very large group; scientists guestimate that there may be as many as a million different types, but so far only about 50,000 have been identified and named; many of these are species that are important to humans in one way or another.
Mites are arthropods, meaning that they have a hardened outer skin and jointed appendages. Within the arthropods, they are distantly related to insects, but more closely related to critters such as spiders and scorpions, with which they form the group we call arachnids.
 |
|
A partially grown Amblyseius californicus
|
Mites have very diverse biologies. Many live in the soil where they feed on microorganisms, fungi, or dead organic matter, or where they prey on other mites, small insects and even nematodes. Others occur in the water where they have similar diverse habits. Gardeners are familiar with those that feed on plants, such as the many species of spider mites or “red spiders”, as well as the gall mites such as those that make the various lumps, bumps, and felty patches on silver maple leaves. Many mites are parasitic on insects or higher animals such as birds, reptiles, and mammals. Ticks, including both the wood tick and deer tick, are types of mites, as is the critter that causes scabies. But mites also provide beneficial services. For example, they are very helpful in the degradation of dead organic matter and therefore play an important role in nutrient recycling. But the group of interest here are the mites that hunt down, kill, and eat various pests of our gardens, landscapes, and ornamental plants. These predatory species, even though they are very tiny and usually overlooked, occur in virtually every landscape and are incredibly important in the natural control and biological control of certain types of plant pests.
The most important group of mites that are predatory on plant-feeding mites is the family Phytoseiidae, with over 2200 known species around the world. There is no common name for this family of mites or any of its members – they are usually just referred to as phytoseiid (fy-toe-see-id) mites based on the scientific name of the family. Although they are sometimes called “predatory mites” this can be a bit misleading as there are many other families of mites that are also predatory.
 |
| Phytoseiulus persimilis female (larger and
darker) and young. |
Almost all phytoseiid mites live on plants. They occur in virtually all plant habitats, but they tend to be more uniformly present in perennial (undisturbed) habitats rather than areas that are cultivated regularly. This is because their small size means they don’t move great distances very fast. In the home garden they are more likely to be seen on roses or apple trees instead of radish plants or marigolds, especially earlier in the growing season. They occur commonly in perennial agricultural commodities such as orchards, vineyards, and forests.
 |
| A young Amblyseius californicus feeding on an egg of twospotted spider mite. |
Like most mites, phytoseiids are very tiny, in the range of about ˝ mm (1/50 of an inch – about the size of the period at the end of this sentence). Because of this, they feed on very small prey. Probably the most important prey of most species includes other types of mites. They readily feed on spider mites, gall mites, and other types of mites that are plant pests. But they also feed on tiny insects, insect eggs, and other tiny arthropods. Amongst insects, they feed on the young crawler stage of scale insects and young thrips, for example.
Phytoseiids are a natural and common component of all healthy gardens. They are helping in pest management throughout the growing season. But there are also ways we can help them do a better job for us. When we make conscious decisions to use the beneficial “natural enemies” of pests, we are practicing what is known as biological control. The following are three types of approaches for using predatory mites in the garden or landscape.
Hypoaspis miles is not a phytoseiid mite, but is a predator from a related family, the Laelapidae. Hypoaspis is an effective predator of the eggs and larvae of fungus gnats, which are often problems in organic soils used for greenhouse plants and house plants.
 |
| A fully grown adult Amblyseius californicus on a leaf vein. |
There are many companies that sell predatory mites. Shipments arrive in temperature-controlled containers and contents are guaranteed to arrive alive. To find sources of predatory mites, type “predator mite” into your internet search engine; several commercial sources should be listed.
In conclusion, tiny predatory mites occur in our gardens as well as virtually all plant habitats world-wide. They are effective predators of plant feeding mites and tiny pest insects. Although they do occur naturally in gardens, their benefits can be increased if we resist using broad spectrum insecticides until they are absolutely needed. For some pest situations, it may be worthwhile to purchase and release predatory mites.
Information on specific products is provided as a service and is not meant to endorse one product over similar products. Remember that pesticide labels are legal documents; any uses not specifically indicated on the label are illegal and may be harmful to people or the environment.
– Dan Mahr, University of Wisconsin - Madison, Department of Entomology
All photos by Merritt Singleton, University of Wisconsin - Madison, Dept. of
Entomology 
| To view pdf documents you need Adobe Acrobat Reader (version 5 or later). If this software is not installed on your computer, you can download a free copy of Acrobat Reader. Click on the logo to go to the website. |
 |
