The Mighty Predatory Mites

These mighty mites are a great entry into using biocontrols. They ship well, are easy to use, and effective. But what is a mite? Mites are tiny arachnids with two body parts, four pairs of legs and sucking mouthparts. These extremely small creatures are about the size of the period at the end of this sentence. They feed on other mites, tiny insects like young thrips and scale, as well as the eggs of insects and mites. Not all predatory mites are the same. This makes them perfect for a greenhouse environment or outdoor crops where change can be constant due to weather, culture, and pest pressure. They land into three categories.

Specialized Mites

These mites feed on a specific pest and will not accept alternative food sources. Phytoseiulus persimilis is a good example of a specialized mite. It feeds actively on the two-spotted spider mite and will disperse when the prey is gone. They tend to aggregate near their prey and will remain longer than other mites while prey is available.

• Phytoseiulus persimilis—Bright red/orange, preys on two spotted spider mite. Can eat up to 20 pest eggs/nymphs per day. Optimum conditions are 68°-81°F with relative humidity (RH) over 60%. Active year round in the greenhouse. This mite can spread across plants when the leaves are touching, but movement is inhibited on plants with smooth leaves (Dianthus) and those with hairy leaves (tomato). 

Selective Mites

These mites prefer one type of prey but will also feed on other food sources such as other mites, insects and pollen. Because of this they can survive at low prey densities. There is crossover between selective mites and generalist mites.

• Amblyseius cucumeris--pear shaped and light tan in color. Feeds on the immature stages of western flower thrips, pollen and pest mites including broad mite, cyclamen mite and tomato russet mite. Optimum conditions are 68°-77°F with RH 66-70%. Development from egg to adults slows significantly with low humidity. 
• Amblyseius degenerans--feeds on thrips and pollen. Similar to cucumeris, degenerans is effective in “harassing” the larval stages of thrips, which may reduce the level of damage caused by thrips feeding. The predatory mite tolerates a lower relative humidity and has a higher population growth than N. cucumeris.
• Neoseiulus californicus--feeds on spider mites, broad mites, cyclamen mites, russet mites and pollen. Well adapted to high temperatures and does best in warm humid conditions. Is an aggressive predator and will eat other beneficial mites. Has a slower population growth than persimilis and is less efficient at finding prey.
• Neoseiulus fallacis-- shiny, tan to light orange with long legs. Feeds on spider mites, rust mites, small insects, and pollen. Can reproduce at lower temperatures than other predatory mites (48°-85°F RH over 50%) 14-60 day lifespan.
• Galendromus occidentalis--pear shaped and white, red or brown depending on coloration of prey. Feeds on spider mites, other pest mites and pollen. Good for fruit trees and outdoor crops. Optimum conditions are 50°-115°F and RH 30-60%. Tolerates higher temperatures and a lower relative humidity better than P. persimilus.   

Generalist Mites

Feed me! These mites will feed on other mites, pollen and plant exudates. Cannibalism is prevalent and one release is often sufficient. This type of mite is more effective when pests are spread out as generalist mites disperse more rapidly.

• Amblyseius swirskii--feeds on thrips and young stages of whitefly, pollen and fungi. It can consume up to 10 thrips, 10 whitefly nymphs or 20 whitefly eggs per day. Optimum temperatures are 77°-82°F with RH of 70%. Studies have shown that A. swirskii is more effective when thrips and whiteflies are present simultaneously.  
• Amblyseius andersoni—feeds on numerous species of mites and thrips. Active under a wide range of temperatures, 43°-104°F making them suitable for early season as well as very hot conditions.
• Stratiolaelaps scimitus lives in the top 1" of soil and feeds on fungus gnat larvae, young stages of thrips, springtails and root mealybug. Optimum soil temperatures 60°-75° Can survive mild winters but are inactive below 57°F. Compatible with beneficial nematode use.

Harassment 

The statistics about harassment from predatory mites are incredible! What a difference mites make! Just having beneficial mites on your crops will reduce pest pressure, even if they aren’t eating the pests. Use of predatory mites reduces:

• Thrips feeding by 25%
• Thrips larval survival by 50%
• Thrips life span by 40%
• Thrips egg laying by 70%
• Thrips plant damage by 30%

As you think about your crops and growing conditions, pick the right mite and watch those pests disappear!

A Breakdown of Aphid Parasitoids and Predatory Mites by Dr. Raymond Cloyd, Grower Talks, 2017. 

Predatory Mites, Colorado State University

When Harassment is a good thing in your Greenhouse, Ontario Floriculture