Excerpted from
THE VEGETABLE AND SMALL FRUIT GAZETTE
October, 2001
Volume 5, No. 10
Bug vs. Bug- Managing Two-Spotted
Spider Mite wth the Predatory Mite
Neoseiulus californicus
Cathy Thomas, Integrated Pest Management Program
Pennsylvania Department of Agriculture
Two- spotted spider mite (Tetranycus urticae), the most common spider
mite species found in PA greenhouse vegetable and herb production, can increase
rapidly especially during hot, dry periods. Most of the difficulty in controlling
this pest is initial detection. Since there is no winged stage, sticky traps
are ineffective, hence, plant inspection is the only method to assess if mites
are present. Damage is caused by larvae, nymphs and adults piercing the plant
cells and sucking out the contents. They are usually found on the on the undersides
of the leaves, and sometimes with silken webbing at high populations. The damaged
cells appear as yellowish white spots (chlorophyll is destroyed) on the upper
surface of the leaf. As populations increase, the whole leaf will eventually
turn yellow. Crop losses may occur when about 30% of the leaf surface is damaged.
There are a limited number of pesticides
available for treatment of this pest in greenhouse vegetable and herb production;
therefore an integrated approach using biological controls in conjunction with
compatible biorational materials is needed. Some materials that can be used
with biocontrols to treat hot spots or reduce populations before introducing
biocontrols include:
Ultra-fine oils, neem oil, insecticidal soap, and the entomopathogenic (insect
killing) fungi Beauveria bassiana. Biological control options include
predatory mites, and predatory midges.
The most commonly used predatory
mite is Phytoseiulus persimilis. This is used in many vegetable and ornamental
crops for quick knockdown of spider mites. The predatory midge, Feltiella
acarisuga is also effective in reducing high populations of spider mites.
Both of these natural enemies require prey to persist and relative humidity
above 60% for reproduction.
If the environmental situation has
high temperatures and variation in humidity (below 60%), an alternative biocontrol
option would be the predatory mite, Neoseiulus (Amblyseius) californicus.
In crops where it is hard to detect spider mite populations, this mite can be
introduced on preventative basis since it can survive in the absence of prey.
Life Cycle of Neoseiulus californicus
The five different stages of this
mite are the egg, larva, protonymph, deutonymph and adult.
The adult predatory mite lives about 20 days and can lay up to 3 eggs a day.
It is able to consume 5 adult spider mites daily in addition to feeding on eggs
and larvae. The life cycle can be completed within 4 days with high temperatures.
Application
ß Start early to control spider
mite populations since spider mites reproduce quickly at high temperatures and
low humidity.
ß If used on a curative basis, introduce N. californicus with Phytoseilus
persimilis to clean up hot spots.
ß Concentrate predator introductions at spider mite hot spots as soon
as possible after delivery.
ß Monitor for predator activity by checking spider mite colonies for larval
development and for shriveled pest mites that have been fed upon. Monitoring
should be done once a week, consistently to determine if future introductions
of predatory mites are needed.
ß Can be used on outdoor crops.
ß N. californicus also attacks the broad mite (Polyphagotarsonemus
latus) and the cyclamen mite (Tarsonemus pallidus).
Products
N. californicus is shipped to the grower as mobile stages.
Some product names from major suppliers include:
ß Spical - www.koppert.nl, 734-641-3763
ß Californicus – system, www.biobest.be,
303-661-9546
ß Neoseiulus californicus – www.syngentabioline.com,
805-986-8265
This predator can be obtained through
most biological control distributors.
Please phone or email me if there
are specific issues you would like me address in this column.
Cathy Thomas
Integrated Pest Management Program
Bureau of Plant Industry/Rm. 100
2301 N. Cameron Street
Harrisburg, PA 17110
717/705-5857
E-mail: c-cthomas@state.pa.us