The two-spotted spider mite (TSSM), Tetranychus urticae Koch (Acari:
Tetranychidae) is common pests on many vegetables and ornamental plants,
including tomatoes, cucumbers, peppers, strawberries, roses and
many other host plant species. It feeds by puncturing cells and draining
the contents, producing a characteristic yellow speckling of the leaf
surface. They also produce silk webbing, which is clearly visible at high
infestation levels (Alzoubi and Çobanogu, 2006). Logically, this
reduces of plant`s ability to build carbohydrates, which thereafter results
reduction in total yield. Measuring damage is very important to identify
economic threshold and set up a good integrated pest management program.
Several methods for estimating T. urticae feeding damage have been
proposed (Tomkiewicz et al., 1993; Iatrou et al., 1995;
Nachman and Zemek, 2002). Recently, digital images and computers have
been used to measure pest feeding (Alchanatis et al., 2000; O`Neal
et al., 2002; Skaloudova et al., 2006). Compu Eye, leaf
and Symptom Area software is one from the software programs to measuring
the feeding damage of T. urticae. Bakr (2005) mentioned that Compu
Eye, leaf and Symptom Area software was able to assess the symptom area
of T. urticae accurately with no significant difference compared
with manual measurement. This software is a simple and relatively inexpensive
method because it does not require any special equipment beyond usual
computer software and hardware. In addition, scanned images can be stored
on digital media (e.g., on CD or USB) for later analysis and the software
saves more time and effort than other mathematical methods, which require
accounting the pest stages before and after application. There are many
formulas available to calculate percentage efficacy against spider mites
and insects. These formulas were used to evaluation the control methods
for choosing in integrated pest management program, such as Abbott, Henderson
and Tilton, Schneider-Orelli or Sun-Shepard formulas. The aim of this
trial is evaluation and comparison between effectiveness of pesticides
and predators as a percentage efficacy by using the Henderson and Tilton
formula with the feeding damage of T. urticae as symptom area rate
by Compu Eye, leaf and Symptom Area software.
MATERIALS AND METHODS
Source of Mites
Tetranychus urticae was reared on bean plants (Phaseolus vulgaris
L.) at 25±1°C. Bean plants were grown under climate room condition
(same regime) and the plants were added weekly to the spider mite culture.
The predatory mites, Phytoseiulus persimilis Athias-Henriot (Acari:
Phytoseiidae) and Amblyseius californicus McGregor (Acari: Phytoseiidae)
were reared at 25±1°C and 60±5% RH under 16 h light
regime on bean plants, which infested with two-spotted spider mites. P.
persimilis was obtained from Hatay Samandag Turkey. A. californicus,
Spical® was obtained from Koppert.
Planting of Host Plants
Cucumber, Cucumis sativus L., plants were used as the host plant
species in greenhouse experiments. Cucumber seedlings were prepared for
planting in gowning room and then transferred to the greenhouse. In greenhouse
experiments the plants were separated from each other to prevent touching
and movement of the mites by using cloth barricades. Thereafter, plants
were infested with TSSM (30 females/plant) when became mature to the four
real leaves phase.
Experiment of Chemical Control
Two insecticide-acaricides (bifenthrin and dimethoate) and a selective
acaricide and mite growth regulator hexythiazox were used. The recommended
field dose of bifenthrin (Talstar® 10 EC, Bayer), dimethoate
(Poligor® 40 EC, Hekta°) and hexythiazox (Twister®
5 EC, Hekta°) which 0.06 g a.i. L-1 (60 ppm), 0.45 g a.i.
L-1 (450 ppm) and 0.05 g a.i. L-1 (50 ppm), respectively.
The experimental dose of the pesticides was one-third of the recommended
field dose i.e., bifenthrin 0.02 g a.i. L-1 (20 ppm), dimethoate
0.15 g a.i. L-1 (150 ppm) and hexythiazox 0.0167 g a.i. L-1
(16.7 ppm). Pesticides were applied 17 days after infestation of TSSM
by using hand sprayer. This experiment was consisted of three blocks,
containing four plants in each block.
Experiment of Biological Control
The predatory mites, P. persimilis and A. californicus
were released four females/plant, after 17 days of infestation. This experiment
was consisted of two blocks, containing four plants in each block.
Experiment of Combination of Chemical and Biological Control
Predatory mites (P. persimilis and A. californicus)
were released i.e., four predatory females per plant, after 17 days from
infestation with TSSM. Thereafter, pesticides were applied with a hand
sprayer after seven days of predators release. This experiment was consisted
of six blocks, containing four plants in each block. In Addition, one
block containing TSSM as control was used for all experiments.
Measuring of Damage Rate
The leaf samples were taken from experimental blocks as four leaves from
each block after 38 days of infestation. Thereafter, each leaf was scanned
individually, on a black background, with 150 DPI (dots per inch) resolutions.
HP scan jet 2400 (Hewlett-Packard, Palo Alto, CO., USA) was used to in
this purpose. Scanned leaf images were saved separately as bmp 24 bit-files.
Compu Eye, leaf and Symptom Area software was used as Bakr (2005) described
it. The software is available now at http://www.ehabsoft.com/CompuEye/LeafSArea.
The principal idea of the software is to divide the image into small squares
and assess the average colour of every square, where the area of these
square units could be adjusted between 0.1 and 1.0 mm2. After
calibration, the standard-shape image files were opened and analysed by
the software, the percentage of symptom area value was calculated for
each leaf image. Data were analyzed with ANOVA using Cohort Software
and means were separated according to Duncan`s Multiple Range Test
Evaluation of Percentage Efficacy
The numbers of TSSM (egg, immature and adult stages) were counted on an
area of 8 cm2 of cucumber leaf in laboratory, using the stero-microscop.
The corrected efficacy percentage was calculated according to Henderson
and Tilton formula (Henderson and Tilton, 1955):
||No. of TSSM population
The leaf samples were taken from experimental blocks in amount of four
leaves from each block before and after 38 days of infestation.
RESULTS AND DISCUSSION
For chemical control treatments, according to ANOVA analysis, the results
of feeding damage values of T. urticae were evaluated in different
three groups (b, ef and c) and there were significant differences within
used pesticides (Table 1). On the other hand, the efficacy
rate of hexythiazox (42.05%) and dimethoate (37.96%) showed significant
difference with the efficacy of bifenthrin (98.70%), result of pesticides
efficacies were evaluated in two groups (d, a). According to the results
of feeding damage rate, it is expected that there is significant difference
(p<0.05) between hexythiazox and dimethoate efficacy, but hexythiazox
is a growth regulator and exposed mite adults to residue may lay eggs
that were not viable (Kenneth et al., 2002) which calculated in
counting. However, in both evaluation methods indicated significant difference
(p<0.05) between bifenthrin with other used pesticides.
||Mean of percentage feeding damage rate and corrected
efficacy (±SE) for treatments of greenhouse experiments
|Split-Plot, Duncan`s test; p = 0.05; r = -0.93 Slope
= 0.0074, Means with different letter(s) within a column were significant
different (p = 0.05. Duncan`s Test)
Results of biological control treatments, the results were evaluated
in one group in both evaluation methods. There was no significant difference
(p<0.05) between treatments of predatory mites (P. persimilis
and A. californicus) in both evaluation methods.
For treatments of combination of chemical and biological control, the
damage rate results of T. urticae indicated no significant difference
between hexythiazox+ predators (P. persimilis and A. californicus)
and bifenthrin+ predators; it was evaluated in one group (ef). This assessment
of results similar with percentage efficacy evaluation and its results
were evaluated in one group (a).
For comparison between control methods, the results of percentage efficacy
showed no significant difference between predators treatments and dimethoate+
P. persimilis, these results were evaluated in one group (c). This
assessment of results similar with the damage rate evaluation and its
results were evaluated in one group (de) (Table 1).
This is concluded from used evaluation methods that, hexythiazox and
dimethoate could not repress the TSSM population, which gave significant
damage rate in its treatments and the efficacy of mention pesticides which
was low, not provided well controlling to TSSM when compared with bifenthrin
and combination between chemical and predators. In addition, bifenthrin
and hexythiazox combined with predators or bifenthrin alone could repress
well the TSSM population so that, the damage rate was low, while its percentage
efficacy was high. Therefore, the data of experiments clearly showed negative
relationship between feeding damage rate and percentage efficacy values
(Correlation Coefficient; r = -0.93). Whenever, the feeding damage rate
has a high value, the percentage efficacy has a low rate.
The satisfactory methods to controlling TSSM population according to
the damage rate were bifenthrin, hexythiazox combined with predators and
bifenthrin alone followed by predators and dimethoate combined with predators.
This assessment has same arrangement to percentage efficacy to controlling
Therefore, the ANOVA analysis of the results of the tested evaluation
methods could separate the mean values of percentage efficacy and feeding
damage rate and relatively assemble into counterpart groups and gave same
decision in evaluation the effectiveness of control methods. Thus, the
computer software (Compu Eye, leaf and Symptom Area) may be satisfactory
recommended for the evaluation of effectiveness of control methods.
Verkerk (2001) reported that the effects of pesticides on natural enemies
were often negative; pesticides can sometimes enhance natural enemy function
particularly, if they are selective against the pests or are used at low
dosages. Wilson et al. (1999) reported that dimethoate had very
low acaricidal activity on TSSM. Kenneth et al. (2002) reported
that hexythiazox had ovicidal action and provide poor control of T.
urticae adults; mortality of T. urticae from hexythiazox and
spinosad residues was not significantly greater than the tested control.
Kim (2001) reported that chemical application could be successfully integrated
with biological control. If there is, a high population density of TSSM
the release of P. persimilis is more effective if a chemical spray
initially reduces TSSM density.
We would like to thank the Scientific and Technical Research Council
of Turkey (TÜBİTAK) who supported this research (No. 105O708).
In addition, to thank Ehab Bakr (Plant Protection Research Institute,
Acarology Department, Dokki, Giza, Egypt) to provide computer software.