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 1:4 predator:prey 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
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
DISCUSSION
Table1. Mean (± SD) number of T. urticae (pest) within three different times *
Treatment
0 day
Even X Even
Even X Clumped
Clumped X Even
.
Clumped X Clumped
Control (Even)
Control (Clumped)
420 ± 17
415 ± 22
422 ± 27
427 ± 12
440 ± 26
449 ± 14
9 days
a
a
a
a
a
a
79 ± 73
93 ± 47
287 ± 46
0±0
1666 ± 249
2805 ± 582
18 days
a
b
c
d
A
B
0±0
a
0±0
a
0±0
a
0±0
a
3383 ± 224 A
4392 ± 827 A
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)
Table2. Mean (± SD) of damage caused by T. urticae within three different times *
Treatment
Even X Even
Even X Clumped
Clumped X Clumped
Clumped X Even
Control (Even)
Control (Clumped)
0 day
2.1 ± 0.13 a
2.05 ± 0.10 a
0.72 ± 0.03 b
0.73 ± 0.03 b
2.03 ± 0.13 a
0.72 ± 0.03 b
9 days
1.37 ± 0.38 a
2.26 ± 0.05 b
0.75 ± 0 a, c
1.01 ± 0.32 c
3.45 ± 0.26 A
2.84 ± 0.28 B
18 days
0.77 ± 0.33 a
2.02 ± 0.03 b
0.53 ± 0.03 a
0.87 ± 0.42 a
4.6 ± 0.44 A
4.03 ± 0.15 A
* (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
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 predator’s 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
METHOD
The experimental unit consisted of 16 impatiens plants arranged in a square (in a
try)( Fig 1)
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
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 1:4 predator: prey ratio
The responses were the total number of T. urticae count and the average of
damage in each try
A
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)
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.
This would give a high chance for prey to cause damage to clean
plants while most of the predators are searching randomly.
The experimental was a randomized complete block design (as a 2X2 factorial: prey
and predators spatial distributions) with three blocks
Therefore, this strategy should be avoided while applying biological
control program
Fig.1. A view of the plants arrangement in one unit: A central plants:
Multiple comparisons procedure (ANOVA one and two ways) of the means for the
• 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
different four treatments and controls in each time for each response was used
other 12 plats were clean (uninfected)
Procedure of creating different patterns of T. urticae and predator P. persimilis • When even (predator): each plant in the unit received same # of predators
• When clumped (predator): only the central plants received all predators.
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)
REFERENCES
Eveleigh, E.S. and Chant, D.A. 1982. Experimental studies on acarine predator–prey
interactions: the distribution of search effort and predation rates of a predator population in
a patchy environment (Acarina: Phytoseiidae). Can. J. Zool. 60: 3001–3009
Jarosik 1990. Phytoseiulus Persimilis and its prey Tetranychus urticae on glasshouse
cucumbers and peppers: key foacors related to biocontrol efficiency. Acta Entomol.
Bohemoslov. 87:414-430
Pallini, A., Janssen, A., Sabelis, M. Odour-mediated responses of phytophagous mites to
conspecific and heterospecific competitors. Oecologia (1997) 110:179-185
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;
P< 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)
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.
At the end of the experiments (time 2):the data showed that there was
Because of high searching ability that predators showed, our results
no significant difference in the number of prey killed ,which was
indicate that releasing the predators randomly may control both pest
completely controlled ( 0), under different even and clumped of prey
and its damage too.
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).
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).