4
 as the plants are established. If fewer plants have spider mites,
 frequent moni oring after planting is essential.
 2. After plant e tablishment. When overhead sprinkling for crop
 establishment as ended, it is important to monitor the spider mite
 population den ity. Examination of 100 leaflets, taken at random across
 the field, usu lly provides a reliable indication of mite densities.
 Since mites co e with the plants, old leaves should be inspected during
 the early part of the season. After the plants have grown two to four
 new leaves, ta e fully expanded leaflets, avoiding the oldest and the
 youngest leafl ts. Pick the leaflet, examine it and determine whether
 any stage of spider mites is present. Record as (+) if so, and as (-)
 if not. This s mple of infested and non-infested leaflets gives.a
 sufficiently ac urate estimate of the average mite density per leaf, and
 indicates the a tion to be taken. Watch for "hot spots" because spider
 mites are often clumped in their distribution patterns. A sample data
 sheet is illust ated at the end of this manual.
 3. After predator r leases. After releasing the predatory mites, monitor
 their presence a d effectiveness. Three to 6 weeks are needed to assess
 their establish nt.

 M nitoring Predatory Mite Densities
For monitoring the pre atory mite population the same procedure as for spider
mite density can be use However, as the numbers of predators shortly after
releasing are much lowe than that of the prey, their number should be
recorded per individual leaflet. A sample of 100 leaflets also provides a
reliable indication of heir presence and activity. During the first 2 weeks
after releasing, the pr dators are difficult to find; two to five mites and
some eggs in a 100 leaflet sample may be expected. After this period the
number of predaceous mit s and their eggs may increase greatly, depending on
the prey density.

 Quality of the Predators to Be Released
The results in our studi s were obtained by releasing the "Koppert" strain of
Ph. persimilis. Predaceous mites are susceptible to various pesticides.
However, there are discre ancies as to the susceptibility or tolerance to
specific pesticides in di ferent strains of Ph. persimilis. Some of the
confusion might be attrib ted to differences is susceptibility to pesticides
between strains from diff rent origins; resistance or tolerance to various
insecticides and miticide as organophosphorus compounds, cyhexatin, and
others have been reported in different strains. Therefore, growers should
consult with their suppli rs as to the sensitivity of their strain to specific
pesticides.

A practical check on quali y or viability of the predators that can be
performed by the grower is to open the bottle, and keep it upright for a few
minutes. If the predators are in good condition a large number of them should
crawl around the opening o the bottle within a few minutes. These must be
mixed again into the vermi ulite before the bottle contents are dispensed.