Spatial distribution of predators and prey affect biological control of twospotted spider mites, Tet

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Spatial distribution of predators and prey affect
biological control of twospotted spider mites,
Tetranychus urticae Koch (Acari Tetranychidae),
using Phytoseiulus persimilis Athias-Henriot
(Acari Phytoseidae) on impatiens

F. J. ALATAWI, D. C.
MARGOLIES, AND J. R. NECHOLS
Kansas State
University, Department of Entomology, 123 West
Waters Hall, Manhattan, Kansas,
66506-4004
ABSTRACT The twospotted spider mite, Tetranychus
urticae, initially occurs in clumps or hot
spots in commercial greenhouses. Growers
concerned about mite damage are often advised to
focus on hot spots either with chemicals or
natural enemies. However, many growers spread
natural enemies evenly around the greenhouse. We
investigated the impact of spider mite
distribution among plants on the effectiveness of
two release strategies of the predatory mite,
Phytoseiulus persimilis for biological control.
The experimental unit consisted of 16 impatiens
plants arranged in a square. Each unit started
with, relatively, the same numbers of spider
mites predators were released at a 14
predatorprey ratio. The experiment was designed
as a 2 x 2 factorial spider mites were
established either in an even or clumped
distribution and predators were released either
in an even or clumped. Predators were able to
totally control spider mite populations to 0 in
less than 9 days in only in Clumped (pest) X
clumped (predator) while spider mite populations
were highly reduced in the Even X Even and Even X
clumped treatments comparing to Clumped X Even.
Yet, even in this (Clumped X Even) case the
number of mites was totally controlled after 18
days as well as other treatments. However,
significant damage was either not controlled or
not significantly reduced except when both the
pest and predator were evenly distributed.
Releasing predators in different patterns
demonstrated that they have the ability to spread
and control the spider mite. For that reason,
growers may only need to release predator in hot
spots, at least early in spider mite
infestations.
INTRODUCTION Density and spatial distribution of
prey are two main factors that affect the release
strategy of predator because they effect all the
other factors However, Eveleigh and Chant
(1982) suggested that the searching ability of a
predator must be evaluated not only in prey
density per unit but also in terms of the
relative distribution of the prey population in
that area The important factors affecting the
outcome of the predator- prey under commercial
greenhouses were not extensively studied (Jarosik
1990) To ascertain the possibilities of
biocontrol, further knowledge of predator- prey
interaction under commercial glasshouse
conditions is necessary To explores the effects
of prey and predators spatial distribution on
efficiency of biocontrol on impatiens plants ,the
design was suggested to imitate the real
situation in commercial greenhouses The overall
goal is to develop a realistic biological control
system of controlling T. urticae in impatience
plants in greenhouse based on the technical and
economical feasibility of pest management
DISCUSSION Results strongly show the high
ability of the P. persimilis to find its prey
then control or at least reduce its population
within short time under different
distributions( Table 1) when both the prey and
predator have same distribution( i.e E X E or
C XC), more prey were killed by the predator when
prey were clumped followed by even distribution
(Table 1) This is because that prey was more
easily discovered by their predators when the
former occurred in groups and the distance
between them was small (Eveleigh and
Chant,1982) This indicates that the actual
distance between the preys is important in
determining the searching success of the
predators However, still this will depend on the
prey population density because at high prey
densities per unit area the spatial distribution
may have little effect on the predators
searching success due to the distance between
being short under such condition (Eveleigh and
Chant,1982) Even though the number of T. urticae
was completely controlled in the end of the
experiments (time 2) in E X C (Table 1), the
damage was not reduced comparing to the time (0)
(Table 2) This shows the importance of
controlling T. urticae within short time which is
considered as the key of having successful
biological control program especially for those
cultivars that have short life cycle like
impatiens It was clear that the predators in C X
E, especially those were released on uninfected
plants, had longer searching time than those
in E X C( because of even distribution of prey in
all neighbor plants) and they were searching
randomly This difference could be explained
based on that fact that predators respond to
herbivore-induced plant volatiles and the
intensity of the volatiles is directly related
the number of potential prey in an area (Pallini
et al. 1996) This would give a high chance for
prey to cause damage to clean plants while
most of the predators are searching
randomly. Therefore, this strategy should be
avoided while applying biological control program

Table1. Mean ( SD) number of T. urticae (pest)
within three different times
.
Table2. Mean ( SD) of damage caused by T.
urticae within three different times
OBJECTIVE Determine the best strategy of
releasing the predators by measuring the ability
of P. persimilis to control T. urticae and
protect plants from visible damage under
different distributions
(N 3 per each treatment ) In each column
when any two or more means have same letter,
they are not different from each other and
capital letters indicate that the compression
only between controls. Capital letter only
for control compression
METHOD The experimental unit consisted of 16
impatiens plants arranged in a square (in a
try)( Fig 1) Spider mites were established
either in an even or clumped distribution and
predators were released either in an even or
clumped Predators were released at a 14
predator prey ratio The responses were the
total number of T. urticae count and the average
of damage in each try Spider mites were sampled
and damage was recorded three times, beginning
when predators were released (time 0) and then
after 9(time 1) and 18 (time 2) days. The
experimental was a randomized complete block
design (as a 2X2 factorial prey and predators
spatial distributions) with three blocks
Multiple comparisons procedure (ANOVA one and
two ways) of the means for the different four
treatments and controls in each time for each
response was used Procedure of creating
different patterns of T. urticae and predator P.
persimilis At Four-wk-old plants of Impatiens
Impulse Orange, randomly and individually, some
plants were each inoculated with six adult
females whereas others were each inoculated with
24 adult females Twelve days after inoculating
plants with T. urticae plants were gathered to
form theses different units. Treatments of
Even (pest) X Even (predator)(E X E), Clumped X
Clumped (C X C), Even X Clumped (E X C), and
Clumped X Even (C X E) were created ( for
details see Fig 1) In addition, tow controls
for even and clumped units (i.e. no predators
were applied on them)

• Fig.1. A view of the plants arrangement in one
  unit A central plants
• When even (pest) each plant in the unit
  inoculated with 6 mites
• When clumped (pest) only the central plants
  each inoculated with 24 mites while the
• other 12 plats were clean (uninfected)
• When even (predator) each plant in the unit
  received same of predators
• When clumped (predator) only the central
  plants received all predators.

CONCLUSION Information about the T. urticae
distribution is required prior to selects and
apply a correct strategy of releasing
predators Economically, detecting the pest
early, while in clumped, will reduces the number
of predators that should be released , decrease
the damage in the hotspots which keep plants
with high value , and most impotently protect
other plants from damage Therefore, growers are
not recommended to spread natural enemies evenly
around the greenhouse. However, since impatiens
is highly susceptible to damage, controlling T.
urticae on impatiens at very low density of T.
urticae is highly recommended Yet,
investigating the hot spots of prey at low
density may be not noticeable. Because of high
searching ability that predators showed, our
results indicate that releasing the predators
randomly may control both pest and its damage
too.
RESULTS Nine days from the time of releasing
predators (time 1) while there was highly
significant difference between (C X C) and
other two treatments ( E X E) (t 4.4 df 6 P
0.004) and (C X E) (t 9.2 df 6 Plt 0.000),
the different between the (E X E) and (C X C)
treatments was not that high significant (t
2.6 df 6 P 0.043) (Table 1). Pest number
was completely controlled only in (C X C)
(Table 1). While there was high significance in
damage between the E X E and E X C (P 0.003),
there was no difference between other two
treatments X C and C X E) (P 0.23) At the end
of the experiments (time 2)the data showed
that there was no significant difference in the
number of prey killed ,which was completely
controlled ( 0), under different even and
clumped of prey and predator distributions (F
0 df 1,6 P 1) ( Table 1) At this time still
there was highly significance different in damage
between E X E and E XC (P 0.0004) while there
was no different between C X C and C X E (P
0.16). Also there was highly significant
different between the damage of C X E
comparing to the damage on other treatments
which they were not different from each other
( Table 2 ).Damage has been clearly reduced
within times was only in the E X E ( Table 2).
REFERENCES Eveleigh, E.S. and Chant,
D.A. 1982. Experimental studies on acarine
predatorprey interactions the distribution of
search effort and predation rates of a predator
population in a patchy environment (Acarina
Phytoseiidae). Can. J. Zool. 60
30013009 Jarosik 1990. Phytoseiulus Persimilis
and its prey Tetranychus urticae on glasshouse
cucumbers and peppers key foacors related to
biocontrol efficiency. Acta Entomol. Bohemoslov.
87414-430 Pallini, A., Janssen, A., Sabelis, M.
Odour-mediated responses of phytophagous mites to
conspecific and heterospecific competitors.
Oecologia (1997) 110179-185
ACKNOWLEDGMENT We thank the following
individuals from Kansas State University for
their contributions Rebhi Bshara, Kiffnie Holt,
Punya Nachappa, Aqeel Ahammed, and Xiaoli Wu. We
acknowledge Syngenta Seeds,Inc., for providing
the plant material used in these experiments.
This project was funded in part by USDAÐNRI
(Project Award No. 00-35316Ð9248) and by
USDADPMAP(Project Award No. 2002-34381D12146).
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