BIOCONTROL OF TWOSPOTTED SPIDER MITE
Biological Control Guidelines
Mark A. Morris and Joyce Takeyasu, A. M. Todd Co.
Note: this information is considered unpublished work and should not be used as final or finished results. It has been included in IPMP 3.0 because it may not be available from other sources, and in some cases may include information that may not reach final publication.
One species of predator mite, Neoseiulus
(Amblyseius) fallacis, is very common in peppermint fields. N.
fallacis adults are somewhat shiny, tan to slightly orange in color, and are
oblong-shaped. They will provide excellent biological control of twospotted spider mites,
if populations are conserved. When populations are disrupted due to incompatible
pesticides or heavy flaming, recolonization usually occurs from habitats surrounding mint
in Western Oregon. In Eastern Oregon, N. fallacis has not been collected on
surrounding vegetation, and is only likely ro recolonize from small refugia within the
field. In addition, this species may also be re-introduced manually. It may be obtained
from biological control supply houses and released in the field to initiate new
populations. Released predators will spread throughout the field over several weeks to
months, depending on the number released and weather conditions. They overwinter in dead
leaves, on stems, and on green foliage in mint, and will provide long term biological
control if not disrupted.
¹ Less toxic if applied by chemigation
with large amounts of water
Elimination of natural enemies by the misuse of pesticides may result in subsequent pesticide applications for other pests. Despite efforts to use disruptive pesticides in a selective manner, it may not always be possible, However, we can keep disruptive of biological control agents to a minimum and also slow the development of pesticide resistance by treating fields only when absolutely necessary.
Heavy (double) flaming of the field will reduce predator densities to near zero, while single flaming usually allows sufficient numbers to survive, so that re-introduction may not be needed. Single flaming may adversely affect predator/prey ratios, however, that can lead to spider mite population flare-ups. (see Morris et al., 2000).
Preliminary release recommendations:
To inoculatively release N. fallacis, spread predators evenly throughout the field, especially towards the upwind side and wherever spider mite densities are highest. If the lower release rates are used, place at least 10-12 healthy female N. fallacis per 5 sq. ft. site, with ca. 30-35 ft. between sites. This rate is equivalent to 500 predators per acre. Apply the predators to the crop as soon as possible after recieving shipments for best results. Note that predator mites will not survive storage, except perhaps for a few days under refrigeration. Avoid making releases when humidities are low. Be sure to check for good, healthy females, which are easy to recognize from their robust, shiny appearance and very active search behavior. Small, dull-colored and sluggish females are not as likely to survive. Contact OSU Entomology Dept. for a list of recommended insectaries and distributors that handle N. fallacis.