Biological control of twospotted spider mites, Tetranychus urticae Koch (Acari: Tetranychidae), using Phytoseiulus persimilis Athias-Henriot (Acari: Phytoseidae) on impatiens

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Biological control of twospotted spider mites,
Tetranychus urticae Koch (Acari Tetranychidae),
using Phytoseiulus persimilis Athias-Henriot
(Acari Phytoseidae) on impatiens F. J.
Alatawi, J.R. Nechols, D.C. Margolies
Department of
Entomology, Kansas State University, Manhattan,
Kansas, 66506-4004,
ABSTRACT  The effectiveness of the predatory
mite, Phytoseiulus persimilis Athias-Henriot
(Acari Phytoseidae), as a suppressive agent of
the twospotted spider mite, Tetranychus urticae
Koch (Acari Tetranychidae), was evaluated on
impatiens plants at predatorprey release ratios
of 127, 1 17 and 14. To determine if initial
pest population size influenced the suppressive
ability of the predator, releases at each
predator prey ratio were made at low and high
T. urticae densities. At these two pest
densities, only the release ratio of 14
significantly reduced both pest numbers and plant
damage after short time . After only one week, P.
persimilis released at a ratio of 14 were able
to reduce T. urticae population densities to
almost negligible levels. Although the release
ratio of 117 was able to prevent further
increase in pest populations, the predators did
not reduce pest numbers or the level of damage
especillay at the high TSM density . Therefore,
for successful biological control of T. urticae
on impatiens, a 14 release ratio P. persimilis
is recommended.
INTRODUCTION Greenhouse-grown impatiens is one
of important ornamental plants in the U.S.A.
and represents part of profitable local
marketNASS 2003 The twospotted mite ((TSM) is
one of major pests of floricultural (ornamental)
crops of economic importance and controlled using
acaricidae sprays (Skirvin and Williams
1999) However, the pressure for the less of
pesticides and the fact that TSM has been showing
resistance to most major acricides have led to
increased use of biological control Skirvin and
Williams 1999 The predatory mite phytoseiulus
persimilis ,in the family phytoseiidae, is an
examples of biological control agents that has
been reared and sold for biological control of
(TSM) The key stumbling block that remains in
the adoption of P. persimilis is lack of grower
management expertise and the quality of the
plants produced is the most important to growers
of ornamental nursery stack (Skirvin and Williams
1999) One way of reducing the ration of cost to
potential loss is to determine the right
predator prey release ration that gives
sufficient pest control at a low pest density As
a result, A predator with a predator prey ration
that works well at low pest density is a good
candidate for developing an IPM program in which
only limited releases of the predator are
performed (Castane et al 1996) Because sales
are based on aesthetics, control TSM to minimize
visible plant damage is critical in floricultural
crops.
Low TSM Density
(B) Damage
(A) Number of TSM
.
Proportion of damaged leaves
Number of TSM/ plant
DAYS
DAYS
Control(0) 128 117 14
High TSM Density
(D) Damage
(C) Number of TSM
Number of TSM/ plant
Proportion of damaged leaves
DAYS
DAYS

• OBJECTIVE
• Determine the predator prey ratio that works
  well for controlling both TSM population and its
  damage within short time after release predators
  on impatiens

RESELTS AND CONCLUSION Over time, there was
significant difference in the means of TSM
number between the three different release
ratios on the same inoculation rate( df
9101,f 12.5, plt 0.001). Also, there was
interaction between week (times) and different
release ratios (df 6 101, f 76.9,
plt0.001.) At low TSM density and after 21 days
from the time of release predators , there was
no differences between the release ratio
(14) and ( 17) in both number of TSM (df 101,
p 0.9 ) and damage( df 107, p 0.06) while
damage was highly significant in high TSM
density( df 107, p lt0.001) at the same time and
ratio. Because impatiens plants are extremely
low tolerance of pest damage and because that a
sequence increase in the number of impatiens
leaves would increase the chance of TSM
escaping ( the searching area that predator
should be covered is increased), it is
necessarily to control the population of TSM
and its damage within very short time. The
release ratio 14 was able to reduce the TSM
number and damage in the two different TSM
densities within only 7 days( Graphs A,B,C, and
d). Therefore, for successful control of TSM
on impatiens, 14 release ratio P. persimilis
is recommended.
ACKNOWLEDGMENT We thank the following
individuals from Kansas State University for
their contributions Kimberly Williams, Kiffnie
Holt, Rebhi Bsharat, Aqeel Ahammed, and Xiaoli
Wu.
PROCEDURE Four-wk-old plants of Impatiens
Impulse Orange were inoculated with 7 and 13
adult female TSM When plants were six wk old,
the total number of TSM on each plant AND damage
were determined Three different release ratios
P. persimilis were applied 128, 117 and 14
For each TSM density, 4 plants were assigned
as control( no predator) Weekly, number of TSM
and damage were taken for each plant The
experimental design was 2 3 factorials
completely randomize design run with repeated
measure.
REFERENCES Castane et al 1996. Management of
western flower thrips on cucumber with Dicyphus
tamaninii (Heteroptera Miridae). Biol-control 7
114-120. National Agricultural Statistics
Service (NASS). 2003. United States Department of
Agriculture Floriculture Crops 2001 Summary. From
National Agricultural Statistics Skirvin and
Williams 1999. Differential effects of plant
species on a mite pest (Tetranychus urticae) and
its predator (Phytoseiulus persimilis)
Implications for biological controlExp.Appli.
Acarology23 497-512
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