Scouting for Two-spotted spider mites and Predatory mites
Wednesday, 31 March 2010 12:56
When scouting, it’s important to be able to tell the difference between pest mite species and beneficial mite species. In general, beneficial predatory mites are very active, fast moving pear-shaped mites. One of the most commonly released predatory mites in greenhouse production is Phytoseiulus persimilis. This beneficial, predatory mite is bright orangish-red, pear-shaped mite is very fast moving compared to the more sedentary, pest species, two-spotted spider mite. The female P. persimilis is about 0.6 mm in length and the male is slightly smaller.
With decreasing day length in the fall, as well as falling temperatures and less available food, female spider mites enter diapause. Females entering diapause become an orange-red color within a few days of becoming an adult. They may overwinter in hoop houses and cooler greenhouses in a dormant stage. During this time, they do not eat, or lay eggs and are less susceptible to pesticides. They are also more difficult for predatory mites to find. By looking at the body shape (which is NOT pear shaped), you can tell the difference between diapausing spider mites compared to P. persimilis mites.
To evaluate whether predatory mites are working, look for shriveled, dried up spider mites plus the presence of predatory mites and their eggs. P. persimilis eggs are oval or “football shaped” and roughly twice the size of spider mite eggs. Eggs are laid close to a food source. When first laid, they are a transparent light pink shade and later turn darker. You may start to see the eggs about two weeks after releasing the beneficial (depending upon temperature).
Spider mite eggs are round or barrel shaped and are often found along the midvein on the underside of leaves. When spider mite eggs are first laid, they are transparent. They turn straw colored near the time of hatching. Eggs hatch into larvae and then two nymphal stages before becoming adults. Larvae are at first colorless and develop color as they feed. Their characteristic body spots are more distinct in the nymphal stage. Spider mite adults are easily recognized by their two dark spots on either side of their body. Eggs, nymphs and adults can be found on the underside of the leaves.
Leanne Pundt, University of Connecticut
