0851996884.pdf

vest), were placed in a small plastic vial and
introduced on a leaf located eight to 14 leaves
away from the spider-mite-infested spot.

Parameters measured

Two treatments were tested initially, each in
five replicates. In one treatment, the spider-
mite-infested leaf was located at the lower
part of the plant and P. persimiliswas intro-
duced on the top leaves of the plant. The sec-
ond treatment was arranged the other way
round, i.e. the infested leaf at the top of the
plant and the predators introduced on the
lower leaves of the plant. Twenty-four hours
after introduction of the predatory mites,
their presence on the spider-mite-infested
leaf (= target leaf) was recorded twice a day,
in the morning and in the afternoon, using a
magnifying glass. This procedure lasted for 7
days. The day on which the first predatory
mite was observed on the target leaf was reg-
istered. At the end of the 7-day period, the
target leaves were detached and examined
under a stereomicroscope in order to count
all P. persimilisstages, i.e. the number of
adults, young stages and eggs.

Results and Discussion: Searching-

capacity Tests

Tables 16.1 and 16.2 show clearly that the ini-
tial tendency of P. persimilis is to move
upward. When introduced on the lower
leaves of the plant, it took the predatory
mites 24 h to reach the target leaf located ten

to 14 leaves above. This trend was recorded

in four out of five replicates (Table 16.1).

After 1 week, all developmental stages of the

predator were present on the target leaf

(Table 16.1). When introduced on the top

leaves of the plant, P. persimilisreached the

spider-mite-infested leaf located eight to 11

leaves downwards in only two out of five

replicates 3 and 5 days following the initial

introduction (Table 16.2).

For the sake of developing a standard

searching-capacity bioassay, we suggest

locating the spider-mite-infested leaf in the

upper part of the plant and introducing P.

persimilisin the lower part of the plant.

Further, for practical releases in the crop, it is

recommended that the predatory mites are

introduced on the lower leaves of the plant,

especially in vertically trellised crops, such

as cucumber, tomato, sweet pepper, etc., so

that they can quickly find their way to the

prey located above.

Results and Discussion: Testing Effect of

Storage

After development of the test, the searching-

ability bioassay was performed to study

whether the predatory mites differ in their

searching ability as a result of storage.

Adults of P. persimilisstored at 8–10°C for 5

and 18 days were compared simultaneously,

using the greenhouse cage test. The results

show no difference between the searching

capacity of predatory mites exposed to short

or long storage periods. In four out of five

replicates, the 5-day-stored adults found

Dispersal Tests for Predatory Mites 227

Table 16.1.Searching ability of Phytoseiulus persimilis(P. p) when placed on the lower leaves of a
cucumber plant with spider mites at the top of the plant.

Situation of P. ppopulation on the
DayP. pfirst found infested leaf after 7 days
Rep. no. Leaf distance* on the infested leaf Adults Young stages Eggs

111 2 1 513

210 1 1 –4

314 1 5 116

411 1 1 32

514 1 4 925

*Between the spider-mite-infested leaf and the leaf on which P. persimiliswas introduced.