Journal of Phytopathology and Pest Management 5(3): 14-28, 2018
pISSN:2356-8577 eISSN: 2356-6507
Journal homepage: http://ppmj.net/
∗
Corresponding author:
Moustafa M.S. Bakry,
E-mail: md.md_sabry@yahoo.com
14
Copyright © 2018
Relationship between the population density of the
white mango scale insect,
Aulacaspis tubercularis
(Newstead) (Hemiptera: Diaspididae) and the yield
loss of mango trees in Luxor Governorate, Egypt
Moustafa M.S. Bakry
1*
, Eman F.M. Tolba
2
1
Scale Insects and Mealybugs Research Department, Plant Protection Research Institute,
Agricultural Research Center, Dokii, Giza, Egypt
2
Plant Protection Department, Faculty of Agriculture, New Valley University, New Valley, Egypt
Abstract
Keywords: Aulacaspis tubercularis, pset population, mango, yield reduction.
15
Introduction
Mango trees are subjected to infestation
by different pests. Among these pests, the
white mango scale insect,
Aulacaspis
tubercularis
(Newstead) (Heimptera:
Diaspididae), which
is considered one of
the most destructive pests of mango trees.
It is now widespread in many mango-
growing countries. This pest injures the
shoots, twigs, leaves, branches and fruits
(sucking plant sap, causing deformations,
defoliation, drying up of young twigs,
dieback, poor blossoming, death of twig
by the action of the toxic saliva) and so
affecting the commercial value of fruits
and their export potential especially to
late cultivars where it causes conspicuous
pink blemishes around the feeding sites
of the scales (Nabil et al., 2012; Sayed,
2012). In nurseries, a severe early stage
infestation retards growth. Young trees
are particularly vulnerable to excessive
leaf loss and death of twigs during the hot
dry weather (El-Metwally et al., 2011).
The heavily infested premature fruits
dropped while the mature fruits became
smaller in size with lacking of juice and
unfit for use. The total death of the plant
can become evident if infestation occurs
as of nursery stage (Abo-Shanab, 2012;
Bakr et al., 2009). In Egypt,
A.
tubercularis
was one of the most serious
scale insect pests on mango trees. It
recorded 27.5% of the scale insects on
mango trees at Qaliobiya Governorate,
Egypt (Bakr et al., 2009). This
investigation aimed to evaluate the
relationship between the insect
population and the infestation incidence
percentages of
A. tubercularis
during four
peaks of its seasonal activity
(independent factors) on percentage of
mango yield loss (dependent factor)
during two seasons (2016/2017 and
2017/2018).
Materials and methods
This investigation was carried out on
mango trees in a private orchard situated
at Esna, Luxor Governorate, Egypt
during the period from August, 2016 to
July, 2018, to clarify the effect of the
infestation levels by
A. tubercularis
on
the yield of Goleck mango variety. The
samples consisted of fifteen Goleck
mango trees (Five uninfested and ten
infested trees, homogeneous in their
infestation with this scale, were selected
from different parts of the orchard). The
selected trees (infested and uninfested)
were approximately the same in age,
height (6-7 m) and received the same
horticultural practices. The infested
mango trees which were selected for
carrying out this experiment were not
exposed to any chemical control
measures before and during the period of
investigation. Regular bimonthly samples
consisted of 20 leaves/tree were chosen
in random from different directions and
levels of the mango trees then transferred
to the laboratory in polyethylene bags for
inspection using a stereo-microscope.
Total numbers of alive insects on upper
and lower surfaces of mango leaves were
counted in each inspection date. The
monthly mean numbers of the total
population of
A.
tubercularis
per leaf
was considered in this study to express
the population size of pest. The yield of
each uninfested and infested mango trees
was assessed. In this investigation, used
different insect expressions, which
articulated the population density of this
pest. Two insect expressions were
utilized,
i.e
., insect population and
incidence of infestation.
16
The infestation incidence or relative
abundance or the percentage of infested
leaves by pest was calculated according
to the formula described by Facylate
(1971):
Where, A = the percentage of infestation
incidence or the percentage of infested
leaves. n = No. of infested leaves in
which the pest appeared. N = Total
number of leaves (Uninfested + Infested)
taken of each inspection date.
Simple regression was used to elucidate
the variability of yield loss that could be
caused by the pest during the four peaks
of seasonal activity. Partial regression
was used to find out the simultaneous
effects of insect activity peaks in
September, November, April and June on
mango yield. The equation of linear
regression was calculated according to
the following formula of Fischer (1950)
and Hosny et al. (1972):
Where: Y
=
Prediction value (Dependent
variable). a
=
Constant (y -
intercept). b
=
Regression coefficient. x
=
Independent
variable.
This method was helpful in obtaining
basic information about the amount of
variability in the yield that could be
attributed to these peaks of activity,
together, which was calculated as
percentage of explained variance
(E.V.%). The partial regression values
indicate the average rate of change in
yield due to a unit change in any of the
four peaks of insect activity. Statistical
analysis in this present work was carried
out by MSTATC Program, 1980. All
figures were done by Microsoft Excel
2010. The amount of yield losses and
damage due to scale insect were
calculated according to the following
equation:
Where: A = Yield for uninfested trees.
B = Yield for infested trees. *Average
yield of mango for uninfested trees were
140 and 145 kg/tree during the first and
the second seasons of the study,
respectively.
Results and Discussion
Seasonal activity of
A. tubercularis
on
mango trees:
The half-monthly counts
of
alive stages of
A. tubercularis
infested
Golck mango trees and the infestation
incidence by pest at the studied district
were recorded during the seasons of
2016/2017 and 2017/2018. Accordingly,
it's better to discuss the peaks of seasonal
activity on the basis of monthly mean
numbers for both of them at the
successive sampling dates.
Seasonal activity of
A. tubercularis
total population:
Data in Table 1
revealed that the peaks of the total
population density of
A. tubercularis
during September, November, April and
June, when the general average of the
population density were 116.64, 147.71,
80.84 and 90.53 individuals/leaf in the
first season and were121.67, 149.57,
88.23 and 92.83 individuals/leaf in the
second season, respectively.
Furthermore, the population density was
17
varied in the four peaks. The second peak
of the pest in November was the biggest
ones in size than that of the other peaks,
but the lowest was recorded in the third
peak in April during the two seasons.
Also, the peaks of the total population of
the pest through the second season was
higher than the first season, which that
might be due to the favorable factor
influences (
i.e.
environmental
conditions,…
etc
.).
Seasonal activity of the infestation
incidence percentages:
The trends of the
infestation incidence percentages and the
population density by
A. tubercularis
(peaks) during the investigation period
were similar and represented in Table (2).
The percentages of infestation incidence
have four peaks occurred in September,
November, April and June with a general
average of 93.83, 95.50, 78.83 and 84.00
% in the first season and of 95.67, 97.00,
82.00 and 84.67% during the second
season, respectively. The results showed
that the percentages of infestation
incidence were varied during the four
peaks. The third peak of the pest which
occurred in April was the lowest one,
whereas the highest one was recorded in
the second peak during November in the
two seasons. Also, the percentages of
infestation incidence through the first
season was small comparing to the
second season, which might be due to the
favorable factor influences (
i.e.
environmental conditions,…
etc
.) (Table
2).
Table 1: Effect of infestation by A. tubercularis total population on the yield of Goleck mango variety during
four peaks of the seasonal activity of the pest during the two seasons (2016/2017 and 2017/2018).
Season
Inspected
trees
Yield (kg)
Yield
reduction
(%)
Peaks of A. tubercularis total population
Average of
population
density
Sept.
Nov.
Apr.
Jun.
2016/2017
1
134
4.29
106.09
141.50
69.86
86.20
100.91
2
130
7.14
112.77
141.98
76.95
86.77
104.62
3
126
10.00
114.31
144.09
79.23
89.71
106.83
4
124
11.43
116.49
144.54
80.09
90.42
107.88
5
120
14.29
116.64
144.76
80.84
91.16
108.35
6
118
15.71
116.64
147.71
80.84
91.17
109.09
7
114
18.57
119.33
147.71
82.69
91.24
110.25
8
110
21.43
120.16
148.92
84.51
92.07
111.42
9
104
25.71
121.81
152.63
85.30
93.02
113.19
10
100
28.57
122.18
163.29
88.13
93.50
116.77
Average
118.00
15.71
116.64
147.71
80.84
90.53
108.93
2017/2018
1
132
8.97
111.34
142.51
80.62
76.23
102.67
2
128
11.72
118.01
142.58
83.63
89.63
108.46
3
124
14.48
119.23
146.58
85.01
92.53
110.84
4
122
15.86
121.67
147.56
86.82
92.55
112.15
5
118
18.62
121.67
147.81
89.29
92.72
112.87
6
116
20.00
121.80
149.57
89.69
94.09
113.79
7
112
22.76
124.31
149.57
90.42
94.73
114.76
8
108
25.52
125.11
150.16
90.98
94.89
115.29
9
104
28.28
126.71
153.98
92.22
97.93
117.71
10
100
31.03
126.82
165.37
93.59
102.94
122.18
Average
116.40
19.72
121.67
149.57
88.23
92.83
113.07
18
Table 2: Effect of infestation by A. tubercularis on the yield of Goleck mango variety during four peaks for
infestation incidence with pest in the two seasons (2016/2017 and 2017/2018).
Season
Inspected
trees
Yield (kg)
Yield
reduction
(%)
Peaks of infestation incidence by A. tubercularis
Average of
infestation
incidence
Sept.
Nov.
Apr.
Jun.
2016/2017
1
134
4.29
90.00
93.33
71.67
78.33
83.33
2
130
7.14
90.00
93.33
76.67
80.00
85.00
3
126
10.00
91.67
93.33
76.67
81.67
85.83
4
124
11.43
91.67
93.33
76.67
81.67
85.83
5
120
14.29
93.33
95.00
78.33
83.33
87.50
6
118
15.71
93.33
95.00
78.33
85.00
87.92
7
114
18.57
95.00
95.00
81.67
85.00
89.17
8
110
21.43
96.67
96.67
81.67
86.67
90.42
9
104
25.71
96.67
100.00
83.33
88.33
92.08
10
100
28.57
100.00
100.00
83.33
90.00
93.33
Average
118.00
118.00
15.71
93.83
95.50
78.83
84.00
2017/2018
1
132
8.97
93.33
95.00
71.67
76.67
84.17
2
128
11.72
93.33
95.00
73.33
81.67
85.83
3
124
14.48
93.33
95.00
80.00
83.33
87.92
4
122
15.86
95.00
96.67
81.67
83.33
89.17
5
118
18.62
95.00
96.67
81.67
85.00
89.59
6
116
20.00
95.00
96.67
83.33
85.00
90.00
7
112
22.76
96.67
96.67
85.00
86.67
91.25
8
108
25.52
96.67
98.33
86.67
86.67
92.08
9
104
28.28
98.33
100.00
86.67
88.33
93.33
10
100
31.03
100.00
100.00
90.01
90.00
95.00
Average
116.40
116.40
19.72
95.67
97.00
82.00
84.67
Effect of the total pest population
density on the yield:
Statistical analysis
of data (Table 3) revealed a highly
significant negative correlation between
the mango yield and the four peaks of the
pest population which were -0.93, -0.91, -
0.94 and -0.93; and -0.93, -0.89, -0.97
and -0.86 during September, November,
April and June peaks during the 1
st
and
2
nd
seasons, respectively. The regression
coefficient (b) of the unit effect indicated
that an increase of one insect per leaf
would decrease the yield of mangos by
2.14, 1.56, 2.05 and 4.28 kg. per tree
through the first season and 2.08, 1.42,
2.46 and 1.31 kg. per tree during the
second season, respectively. The exact
relationship between the peaks and the
yield of mango was determined by the
partial regression coefficient values
(Table 3). It was an insignificant
negative regression in the first season (-
2.93, and -0.94) during the peaks of
September and June and was a
significant negative regression (-1.03)
during the peak of November and an
insignificant positive regression (+2.20)
during the peak of April. Likewise the
partial correlation were -0.68, -0.86, +
0.57 and -0.36 during the peaks of
September, November, April and June in
the first season, respectively. While, the
peaks of the pest activity during the
second season (2017/2018) exposed
insignificant negative relation (P. reg. = -
1.77 and -0.79) during the peaks of
September and April, respectively and
significant negative effect (P. reg. = -
0.73) in November and insignificant
positive relation (P. reg. = +0.82) in
19
June. The values of the partial correlation
were -0.69, -0.84, -0.43 and +0.72 during
September, November, April and June
peaks, respectively.
Table 3: Different models of correlation and regression analyses for describing the relationship between the density of A.
tubercularis population and the mango yield during the two seasons (2016/2017 and 2017/2018).
Season
Tested counts
Simple correlation and regression
values
Partial correlation and regression
values
Analysis variance
r
b
S.E
t
P. cor.
P. reg.
S.E
t
F values
C.V.
MR
R
2
E.V.%
2016 / 2017
Average no. of
individuals/leaf
(September)
-0.93 **
-2.14 **
0.30
-7.08 **
-0.68
-2.93
1.41
-2.07
46.24 **
0.02
0.99
0.97
97.37
Average no. of
individuals/leaf
(November)
-0.91 **
-1.56 **
0.26
-6.10 **
-0.86 *
-1.03 *
0.27
-3.82 *
Average no. of
individuals/leaf
(April)
-0.94 **
-2.05 **
0.27
-7.49 **
0.57
2.20
1.42
1.55
Average no. of
individuals/leaf
(June)
-0.93 **
-4.28 **
0.59
-7.27 **
-0.36
-0.94
1.09
-0.86
2017 / 2018
Average no. of
individuals/leaf
(September)
-0.93 **
-2.08 **
0.29
-7.25 **
-0.69
-1.77
0.83
-2.12
65.41 **
0.02
0.99
0.98
98.12
Average no. of
individuals/leaf
(November)
-0.89 **
-1.42 **
0.26
-5.52 **
-0.84 *
-0.73 *
0.21
-3.43 *
Average no. of
individuals/leaf
(April)
-0.97 **
-2.46 **
0.23
-10.80**
-0.43
-0.79
0.76
-1.05
Average no. of
individuals/leaf
(June)
-0.86 **
-1.31 **
0.27
-4.78 **
0.72
0.82
0.35
2.31
r = Simple correlation; P. cor. = Partial correlation; MR = Multiple correlation; b = Simple regression; P. reg. = Partial
regression; C.V. = Coefficient of Variation; R
2
= Coefficient of determination; E.V% = Explained variance; S.E =
Standard error; * Significant at P ≤ 0.05; **Highly significant at P ≤ 0.01.
The calculated partial regression values
indicated simultaneously effects of the
four peaks of insect population on the
mango yield during the two seasons of
2016/2017 and 2017/2018. The results
showed that the combined effect of the
pest activity peaks on the mango yield
during the 1
st
and 2
nd
seasons was highly
significant (Table 3). The amount of the
variability that could be attributed to the
combined effect of these peaks on the
mango yield was expressed as explained
variance percentage (E.V. %), which was
97.37 and 98.12% during the two
seasons, respectively. The remaining
unexplained variances are assumed to be
due to other undetermined factor
influences.
Effect of the pest infestation incidence
on the yield:
Data, in Table (4), showed
that the percentages of infestation
incidence had a highly significant
negative effect on the yield of mango
since the correlation coefficient were (-
0.98, -0.93, -0.95 and -0.99 and -0.96, -
0.94, -0.95 and -0.95) during the peaks
of September, November, April and June
for the first and second seasons,
respectively. The regression coefficient
of the unit effect indicates that an
increase of 1%
in the percentages of
infestation incidence would decrease the
yield by 3.34, 3.96, 2.86 and 2.97 kg. per
tree through the first season and 4.45,
5.21, 1.71 and 2.65 kg. per tree during
the second season in September,
20
November, April and June peaks,
respectively. The real effect of the
infestation incidence appears from the
partial regression (P. reg.) values in
Table, 4, which showed an insignificant
negative effect (P. reg. =
-
0.81, -0.61 and
-0.58) in peaks of September, November
and April, respectively, except a
significant negative relation in June (P.
reg. =
-
1.35) during the first season.
While the second season emphasized
insignificant negative relation (P. reg. = -
1.27, -1.32, -0.41 and -0.81) during
September, November, April and June
peaks, respectively. Also, the values of
the partial correlation were -0.66, -0.66,
-0.70 and -0.78 for the first season and -
0.50, -0.48, -0.46 and -0.56 for the
second season during September,
November, April and June peaks,
respectively (Table 4). The results
showed that the combined effect of the
pest activity peaks on mango yield
during the two seasons were highly
significant for the two seasons (Table,
4). The combined influence of these
peaks of the pest was expressed as
E.V.%, which were 99.63 and 98.43 %
during the two successive seasons,
respectively.
Table 3: Different models of correlation and regression analyses for describing the relationship between the infestation
incidence by A. tubercularis and the yield of mango during the two seasons (2016/2017 and 2017/2018).
Season
Tested counts
Simple correlation and regression
values
Partial correlation and regression
values
Analysis variance
r
b
S.E
t
P. cor.
P. reg.
S.E
t
F values
C.V.
MR
R
2
E.V.%
2016 / 2017
Average no. of
individuals/leaf
(September)
-0.98**
-3.34**
0.24
-13.67**
-0.66
-0.81
0.41
-1.98
332.48**
0.01
0.998
0.996
99.63
Average no. of
individuals/leaf
(November)
-0.93**
-3.96**
0.53
-7.44**
-0.66
-0.61
0.31
-1.97
Average no. of
individuals/leaf
(April)
-0.95**
-2.86**
0.33
-8.77**
-0.70
-0.58
0.26
-2.22
Average no. of
individuals/leaf
(June)
-0.99**
-2.97**
0.12
-25.04**
-0.78
-1.35 *
0.49
-2.74 *
2017 / 2018
Average no. of
individuals/leaf
(September)
-0.96**
-4.45**
0.47
-9.45**
-0.50
-1.27
0.98
-1.29
78.31 **
0.02
0.99
0.98
98.43
Average no. of
individuals/leaf
(November)
-0.94**
-5.21**
0.64
-8.11**
-0.48
-1.32
1.08
-1.22
Average no. of
individuals/leaf
(April)
-0.95**
-1.71**
0.19
-8.93**
-0.46
-0.41
0.36
-1.17
Average no. of
individuals/leaf
(June)
-0.95**
-2.65**
0.31
-8.66**
-0.56
-0.81
0.53
-1.52
r = Simple correlation; P. cor. = Partial correlation; MR = Multiple correlation; b = Simple regression; P. reg. = Partial
regression; C.V. = Coefficient of Variation; R
2
= Coefficient of determination; E.V% = Explained variance; S.E =
Standard error; * Significant at P ≤ 0.05; **Highly significant at P ≤ 0.01.
These findings are in a great agreement
with those reported by Hernandez et al.
(2002). They found a positive correlation
between fruit infestation and yield loss at
harvest among consecutive seasons,
when they studied the relationship
between the population densities of
Aonidiella aurantii
(Mask.)
and the yield
21
of citrus trees.
Prediction of mango yield and its loss:
Prediction equations for the yield of
mango and its losses were calculated
according to the statistical analysis and
presented as follow:
1.
The total population density during
the four peaks versus the yield of
mango:
Y= 448.67** 3.14 x
1
**
1.13 x
2
** + 1.85 x
3
**
+ 0.60 x
4
;
E.V.% = 93.42%
2.
The total population density during
the four peaks versus the percentages
of reduction in mango yield:
Y=
194.34** + 1.62 x
1
** + 0.67 x
2
**
0.57 x
3
0.35 x
4
; E.V. %= 95.58%.
3.
The infestation incidence of the pest
during the four peaks versus the yield
of mango:
Y= 408.2** 0.68 x
1
0.63 x
2
0.05 x
3
1.91 x
4
**; E.V.
%= 96.76%.
4.
The infestation incidence of the pest
during the four peaks versus the
percentages of reduction in mango
yield:
Y= 206.4** + 0.92 x
1
** +
0.61 x
2
* + 0.34 x
3
** + 0.61 x
4
**;
E.V. %= 98.97%.
Where: Y= Prediction value. E.V. %
= Explained variance. X
1
= peak in
September. X
2
= peak in November.
X
3
= peak in June. X
4
= peak in April.
*
Significant at P ≤ 0.05.
**
Highly
significant at P ≤ 0.01.
The aforementioned results on the effect
of the four peaks for the pest population
or infestation incidence by the pest on
the yield of mango and its losses during
the two successive seasons emphasize
that the effect of these factors varied
from season to another which this might
be due to many factors
i.e.
environmental conditions (level, time
and the ability of variety to infestation).
The calculated yield:
The simple linear
regression equations were applied to
estimate the expected yield of mango
Results in Tables (5 and 6) indicated that
the maximum yield (134 kg) was
recorded with the lowest values of total
density of population and the infestation
incidence percentages in the all peaks of
seasonal activity through the two
seasons. While, the minimum yield (100
kg) was estimated with the highest
values of the total density of population
and the percentages of infestation
incidence in the four peaks of activity
during the two seasons (inverted
relation). As well as, when the mango
yields were correlated with the general
average of the total population density of
the pest during the four peaks for
activity; the yield decreased by 2.44 and
1.90 kg/tree. Also, the infestation
incidence of the pest reduced the yield
by 3.44 and 3.12 kg/tree during two
seasons. Data indicated that the mango
yield quantity of the first season
(2016/2017) was higher than that
recorded in the second one (2017/2018).
The differences may be attributed to
many factors, e.g. the pest infestation
and natural reasons. These results are
similar to those obtained by Mohamed
and Asfoor (2004), in Egypt, however
with different host, they studied the
effect of the red scale,
A. aurantii
infestation and the yield loss on citrus
trees and found that the reduction in
22
Valencia orange was higher than that of
Navel. As well as, the damage was
estimated as % reduction in the yield per
tree by 31.14 and 27.15%, respectively.
Table 5: Gradual decrease in yield with the population density increase of the total population of A. tubercularis
during four peaks for seasonal activity in the two years (2016/2017 and 2017/2018).
Season
Inspected trees
Yield (kg)
September
November
April
June
General average
No. of
insects / leaf
Calculated
yield
No. of
insects / leaf
Calculated
yield
No. of
insects / leaf
Calculated
yield
No. of
insects / leaf
Calculated
yield
No. of
insects / leaf
Calculated
yield
2016/2017
1
134
106.1
140.5
141.5
127.7
69.9
140.6
86.2
136.5
100.9
137.6
2
130
112.8
126.3
142.0
127.0
76.9
126.0
86.8
134.1
104.6
128.5
3
126
114.3
123.0
144.1
123.7
79.2
121.3
89.7
121.5
106.8
123.1
4
124
116.5
118.3
144.5
122.9
80.1
119.6
90.4
118.5
107.9
120.6
5
120
116.6
118.0
144.8
122.6
80.8
118.0
91.2
115.3
108.4
119.4
6
118
116.6
118.0
147.7
118.0
80.8
118.0
91.2
115.2
109.1
117.6
7
114
119.3
112.3
147.7
118.0
82.7
114.2
91.2
114.9
110.2
114.8
8
110
120.2
110.5
148.9
116.1
84.5
110.5
92.1
111.4
111.4
111.9
9
104
121.8
107.0
152.6
110.3
85.3
108.8
93.0
107.3
113.2
107.6
10
100
122.2
106.2
163.3
93.6
88.1
103.0
93.5
105.3
116.8
98.9
2017/2018
1
132
111.3
137.9
142.5
126.4
80.6
135.1
76.2
138.2
102.7
136.2
2
128
118.0
124.0
142.6
126.3
83.6
127.7
89.6
120.6
108.5
125.2
3
124
119.2
121.5
146.6
120.7
85.0
124.3
92.5
116.8
110.8
120.6
4
122
121.7
116.4
147.6
119.2
86.8
119.9
92.6
116.8
112.2
118.2
5
118
121.7
116.4
147.8
118.9
89.3
113.8
92.7
116.5
112.9
116.8
6
116
121.8
116.1
149.6
116.4
89.7
112.8
94.1
114.7
113.8
115.0
7
112
124.3
110.9
149.6
116.4
90.4
111.0
94.7
113.9
114.8
113.2
8
108
125.1
109.2
150.2
115.6
91.0
109.6
94.9
113.7
115.3
112.2
9
104
126.7
105.9
154.0
110.1
92.2
106.6
97.9
109.7
117.7
107.6
10
100
126.8
105.7
165.4
93.9
93.6
103.2
102.9
103.1
122.2
99.1
The calculated reduction in yield:
The
simple linear regression equations were
used to determine the prospect reduction
in yield of mango are represented in
Tables (7 and 8). Data in Tables (7 and
8) showed that the least loss percentage
in yield (4.3 and 9.0%) was recorded
with the lowest levels for the population
density or the percentages of infestation
incidence in all peaks of the seasonal
activity during the two seasons. While,
the highest loss percentages in yield
(28.6 and 31.0%) was estimated with the
highest values of the total population
density and the percentages
of
infestation incidence in the four peaks of
the seasonal activity during the two
seasons, respectively (positive relation).
23
Table 6: Gradual decrease in yield with increase of the infestation incidence percentages by A. tubercularis
during four peaks for seasonal activity in the two years (2016/2017 and 2017/2018).
Season
Inspected trees
Yield (kg)
September
November
April
June
General average
% infestation
incidence
Calculated
yield
% infestation
incidence
Calculated
yield
% infestation
incidence
Calculated
yield
% infestation
incidence
Calculated
yield
% infestation
incidence
Calculated
yield
2016/2017
1
134
90.0
130.8
93.3
126.6
71.7
138.5
78.3
134.8
83.3
134.2
2
130
90.0
130.8
93.3
126.6
76.7
124.2
80.0
129.9
85.0
128.5
3
126
91.7
125.2
93.3
126.6
76.7
124.2
81.7
124.9
85.8
125.6
4
124
91.7
125.2
93.3
126.6
76.7
124.2
81.7
124.9
85.8
125.6
5
120
93.3
119.7
95.0
120.0
78.3
119.4
83.3
120.0
87.5
119.9
6
118
93.3
119.7
95.0
120.0
78.3
119.4
85.0
115.0
87.9
118.4
7
114
95.0
114.1
95.0
120.0
81.7
109.9
85.0
115.0
89.2
114.1
8
110
96.7
108.5
96.7
113.4
81.7
109.9
86.7
110.1
90.4
109.8
9
104
96.7
108.5
100.0
100.2
83.3
105.1
88.3
105.1
92.1
104.1
10
100
100.0
97.4
100.0
100.2
83.3
105.1
90.0
100.2
93.3
99.8
2017/2018
1
132
93.3
126.8
95.0
126.8
71.7
134.1
76.7
137.6
84.2
134.1
2
128
93.3
126.8
95.0
126.8
73.3
131.2
81.7
124.3
85.8
128.9
3
124
93.3
126.8
95.0
126.8
80.0
119.8
83.3
119.9
87.9
122.4
4
122
95.0
119.4
96.7
118.1
81.7
117.0
83.3
119.9
89.2
118.5
5
118
95.0
119.4
96.7
118.1
81.7
117.0
85.0
115.5
89.6
117.2
6
116
95.0
119.4
96.7
118.1
83.3
114.1
85.0
115.5
90.0
115.9
7
112
96.7
111.9
96.7
118.1
85.0
111.3
86.7
111.1
91.3
112.0
8
108
96.7
111.9
98.3
109.4
86.7
108.4
86.7
111.1
92.1
109.4
9
104
98.3
104.5
100.0
100.8
86.7
108.4
88.3
106.7
93.3
105.5
10
100
100.0
97.1
100.0
100.8
90.0
102.7
90.0
102.3
95.0
100.3
Table 7: Gradual increase in yield loss with the population density increase of the total population of A.
tubercularis during four peaks for seasonal activity in the two years (2016/2017 and 2017/2018).
Season
Inspected trees
% Yield reduction
September
November
April
June
General average
No. of
insects / leaf
Calculated
reduction
No. of
insects / leaf
Calculated
reduction
No. of
insects / leaf
Calculated
reduction
No. of
insects / leaf
Calculated
reduction
No. of
insects / leaf
Calculated
reduction
2016/2017
1
4.3
106.1
-0.4
141.5
8.8
69.9
-0.4
86.2
2.49
100.9
1.7
2
7.1
112.8
9.8
142.0
9.3
76.9
10.0
86.8
4.23
104.6
8.2
3
10.0
114.3
12.2
144.1
11.7
79.2
13.3
89.7
13.22
106.8
12.1
4
11.4
116.5
15.5
144.5
12.2
80.1
14.6
90.4
15.40
107.9
13.9
5
14.3
116.6
15.7
144.8
12.4
80.8
15.7
91.2
17.65
108.4
14.7
6
15.7
116.6
15.7
147.7
15.7
80.8
15.7
91.2
17.69
109.1
16.0
7
18.6
119.3
19.8
147.7
15.7
82.7
18.4
91.2
17.91
110.2
18.0
8
21.4
120.2
21.1
148.9
17.1
84.5
21.1
92.1
20.46
111.4
20.0
9
25.7
121.8
23.6
152.6
21.2
85.3
22.3
93.0
23.35
113.2
23.1
10
28.6
122.2
24.2
163.3
33.1
88.1
26.4
93.5
24.81
116.8
29.4
2017/2018
1
9.0
111.3
4.9
142.5
12.8
80.6
6.8
76.2
4.7
102.7
6.1
2
11.7
118.0
14.5
142.6
12.9
83.6
11.9
89.6
16.8
108.5
13.7
3
14.5
119.2
16.2
146.6
16.8
85.0
14.3
92.5
19.5
110.8
16.8
4
15.9
121.7
19.7
147.6
17.8
86.8
17.3
92.6
19.5
112.2
18.5
5
18.6
121.7
19.7
147.8
18.0
89.3
21.5
92.7
19.6
112.9
19.5
6
20.0
121.8
19.9
149.6
19.7
89.7
22.2
94.1
20.9
113.8
20.7
7
22.8
124.3
23.5
149.6
19.7
90.4
23.5
94.7
21.4
114.8
21.9
8
25.5
125.1
24.7
150.2
20.3
91.0
24.4
94.9
21.6
115.3
22.6
9
28.3
126.7
27.0
154.0
24.1
92.2
26.5
97.9
24.3
117.7
25.8
10
31.0
126.8
27.1
165.4
35.2
93.6
28.8
102.9
28.9
122.2
31.7
24
Furthermore, when the percentages of
reduction in mango yield were correlated
with the general average of total
population density of the pest through
the four peaks; the percentages of yield
reduction was increased by 1.74 and
1.31%. Also, the percentages of
infestation incidence of the pest
increased the yield loss by about 2.46
and 2.15% during the two seasons,
respectively). These results were
coincided with those obtained by Salman
and Bakry (2012) in Egypt, however
with different insect species and different
host, they reported that the increase in
population density of the mealybug,
Icerya seychellarum
in population peaks
decreased the yield gradually (inverted
relation) by 3.6, 6.5 and 4.3 kg/tree and
2.5, 4.1 and 2.3 kg/tree during two
successive season, respectively and
increased the percentage of the yield loss
by 1.47, 2.64 and 1.77 % and 1.47, 1.97
and 1.08 % when the yield data were
correlated with the peaks of insect
population in October, May and August
through the two successive seasons
(2010-2012), respectively.
Table 8: Gradual increase in yield loss with increase of the infestation incidence percentages by A. tubercularis
during four peaks for seasonal activity in the two years (2016/2017 and 2017/2018).
Season
Inspected trees
% Yield reduction
September
November
April
June
General average
% infestation
incidence
Calculated
reduction
% infestation
incidence
Calculated
reduction
% infestation
incidence
Calculated
reduction
% infestation
incidence
Calculated
reduction
% infestation
incidence
Calculated
reduction
2016/2017
1
4.3
90.0
6.6
93.3
9.6
71.7
1.1
78.3
3.7
83.3
4.1
2
7.1
90.0
6.6
93.3
9.6
76.7
11.3
80.0
7.2
85.0
8.2
3
10.0
91.7
10.5
93.3
9.6
76.7
11.3
81.7
10.8
85.8
10.3
4
11.4
91.7
10.5
93.3
9.6
76.7
11.3
81.7
10.8
85.8
10.3
5
14.3
93.3
14.5
95.0
14.3
78.3
14.7
83.3
14.3
87.5
14.4
6
15.7
93.3
14.5
95.0
14.3
78.3
14.7
85.0
17.8
87.9
15.4
7
18.6
95.0
18.5
95.0
14.3
81.7
21.5
85.0
17.8
89.2
18.5
8
21.4
96.7
22.5
96.7
19.0
81.7
21.5
86.7
21.4
90.4
21.5
9
25.7
96.7
22.5
100.0
28.5
83.3
24.9
88.3
24.9
92.1
25.6
10
28.6
100.0
30.4
100.0
28.5
83.3
24.9
90.0
28.5
93.3
28.7
2017/2018
1
9.0
93.3
12.6
95.0
12.5
71.7
7.5
76.7
5.1
84.2
7.5
2
11.7
93.3
12.6
95.0
12.5
73.3
9.5
81.7
14.2
85.8
11.1
3
14.5
93.3
12.6
95.0
12.5
80.0
17.4
83.3
17.3
87.9
15.6
4
15.9
95.0
17.7
96.7
18.5
81.7
19.3
83.3
17.3
89.2
18.3
5
18.6
95.0
17.7
96.7
18.5
81.7
19.3
85.0
20.3
89.6
19.2
6
20.0
95.0
17.7
96.7
18.5
83.3
21.3
85.0
20.3
90.0
20.1
7
22.8
96.7
22.8
96.7
18.5
85.0
23.3
86.7
23.4
91.3
22.8
8
25.5
96.7
22.8
98.3
24.5
86.7
25.2
86.7
23.4
92.1
24.6
9
28.3
98.3
27.9
100.0
30.5
86.7
25.2
88.3
26.4
93.3
27.3
10
31.0
100.0
33.0
100.0
30.5
90.0
29.2
90.0
29.5
95.0
30.8
Also, Bakry and Mohamed (2015)
mentioned that the increase in the
population density in the four peaks of
the pest population decreased the yield
gradually by 1.37, 1.47, 4.25 and 1.77
kg/treeand 1.45, 1.53, 4.66 and 1.85
kg/tree during two successive seasons,
respectively and increased the
percentage of the yield loss by 0.55,
0.59, 1.70 and 0.71 % and 0.60, 0.63,
25
1.90 and 0.76 %; when the yield data
were linked with the peaks of the pest
population in October, December, April
and July through two successive seasons,
2016-2017 and 2017-2018, respectively.
Expected values in the yield and its
loss with increasing the pest
population or infestation:
Concerning,
the comparison between the peaks of the
pest population or infestation incidence
of
A. tubercularis
and their effect on the
yield of mango during the two
successive seasons (2016/2017 and
2017/2018), was depending on the total
number of the pest per leaf for all peaks
of the population or the infestation
incidence (Tables 9 and 10).
Table 9: Expected values with (decrease or increase) in the yield with increase the rates of infestation by A.
tubercularis total population during four peaks in the two seasons (2016/2017 and 2017/2018).
Season
No. of
insects/
leaf
Calculated yield
% Yield reduction
Sept.
Nov.
Apr.
Jun.
Sept.
Nov.
Apr.
Jun.
2016/2017
15
335.01
325.51
253.29
441.63
-139.30
-132.52
-80.92
-215.4
30
302.98
302.06
222.47
377.35
-116.42
-115.76
-58.91
-169.5
45
270.96
278.60
191.65
313.08
-93.55
-99.01
-36.89
-123.6
60
238.93
255.15
160.83
248.81
-70.67
-82.26
-14.88
-77.7
75
206.91
231.69
130.01
184.53
-47.80
-65.50
7.14
-31.8
90
174.88
208.24
99.19
120.26
-24.92
-48.75
29.15
14.1
105
142.86
184.78
68.37
55.99
-2.04
-32.00
51.17
60.0
120
110.83
161.33
37.55
-8.29
20.83
-15.24
73.18
105.9
135
78.81
137.87
6.73
-72.56
43.71
1.51
95.20
151.8
150
46.78
114.42
-24.10
-136.84
66.58
18.27
117.22
197.8
165
14.76
90.96
-54.92
-201.11
89.46
35.02
139.23
243.7
Mean
90.00
174.88
208.24
99.19
120.26
-24.92
-48.75
29.15
14.11
2017/2018
15
338.46
307.91
296.62
218.39
-133.42
-112.35
-104.57
-50.61
30
307.24
286.56
259.70
198.74
-111.89
-97.63
-79.11
-37.06
45
276.01
265.22
222.79
179.08
-90.35
-82.90
-53.65
-23.50
60
244.78
243.87
185.87
159.42
-68.82
-68.18
-28.19
-9.94
75
213.56
222.52
148.95
139.76
-47.28
-53.46
-2.72
3.61
90
182.33
201.17
112.03
120.11
-25.75
-38.74
22.74
17.17
105
151.10
179.82
75.11
100.45
-4.21
-24.01
48.20
30.73
120
119.87
158.48
38.20
80.79
17.32
-9.29
73.66
44.29
135
88.65
137.13
1.28
61.13
38.86
5.43
99.12
57.84
150
57.42
115.78
-35.64
41.48
60.40
20.16
124.58
71.40
165
26.19
94.43
-72.56
21.82
81.93
34.88
150.04
84.96
Mean
90.00
182.33
201.17
112.03
120.11
-25.75
-38.74
22.74
17.17
Effect of total population density:
The
results revealed that the total population
density of pest in peak of April was more
effective causing the lowest expected
values in mango yield with an average of
99.19 and 112.03 kg/tree through the two
successive seasons, respectively. While,
the peak of total population in November
was the least effective causing the
highest expected values in mango yield
with an average of 208.24 and 201.17
kg/tree during the two successive
seasons, respectively (Table 9). As
regarding, the prospective values with
(increase or decrease) in the percentage
of the yield loss with increasing the
26
infestation rates by
A. tubercularis
during the two successive seasons (Table
9). The results showed that the total
population density during November
peak was least effective causing the least
percentages of reduction in mango yield
with an average of -48.75 and -38.74%
during the two successive seasons,
respectively. But, the pest population
was more effective during April peak
causing the greatest loss in mango yield
with an average of 29.15 and 22.74%
during the two successive seasons,
respectively.
Table 10: Expected values (decrease or increase) in the yield with increase of the infestation incidence
percentages by A. tubercularis during four peaks for seasonal activity in the two seasons (2016/2017 and
2017/2018).
Season
Infestation
Incidence
(%)
Calculated yield
% Yield reduction
Sept.
Nov.
Apr.
Jun.
Sept.
Nov.
Apr.
Jun.
2016/2017
10
398.27
456.90
314.67
338.00
-184.47
-226.36
-124.76
-141.42
20
364.84
417.26
286.10
308.27
-160.59
-198.04
-104.35
-120.19
30
331.41
377.63
257.53
278.54
-136.71
-169.73
-83.95
-98.95
40
297.98
337.99
228.96
248.81
-112.83
-141.42
-63.54
-77.72
50
264.55
298.35
200.39
219.08
-88.96
-113.11
-43.13
-56.48
60
231.11
258.71
171.81
189.35
-65.08
-84.79
-22.72
-35.24
70
197.68
219.07
143.24
159.62
-41.20
-56.48
-2.31
-14.01
80
164.25
179.44
114.67
129.89
-17.32
-28.17
18.09
7.23
90
130.82
139.80
86.10
100.16
6.56
0.15
38.50
28.46
100
97.39
100.16
57.53
70.43
30.44
28.46
58.91
49.70
Mean
55.00
247.83
278.53
186.10
204.22
-77.02
-98.95
-32.93
-45.86
2017/2018
10
497.51
570.00
239.68
314.07
-243.11
-293.10
-65.29
-116.60
20
453.02
517.86
222.56
287.59
-212.43
-257.15
-53.49
-98.34
30
408.54
465.73
205.44
261.12
-181.75
-221.19
-41.68
-80.09
40
364.05
413.59
188.32
234.64
-151.07
-185.23
-29.87
-61.83
50
319.56
361.45
171.20
208.17
-120.39
-149.28
-18.06
-43.57
60
275.07
309.31
154.07
181.70
-89.70
-113.32
-6.25
-25.31
70
230.58
257.17
136.95
155.22
-59.02
-77.36
5.55
-7.05
80
186.10
205.04
119.83
128.75
-28.34
-41.40
17.36
11.20
90
141.61
152.90
102.71
102.27
2.34
-5.45
29.17
29.46
100
97.12
100.76
85.59
75.80
33.02
30.51
40.98
47.72
Mean
55.00
297.32
335.38
162.63
194.93
-105.04
-131.30
-12.16
-34.44
Effect of infestation incidence by pest:
A similar trend in the percentages of
infestation incidence of the pest on the
yield and its reduction was observed and
represented in Table (10). The infestation
incidence during the peak of November
was the least effective causing the
highest expected values in mango yield
with an average of 278.53 and 335.38
kg/tree during the two successive
seasons, respectively. While, the peaks in
April was more effective causing the
lowest expected values in mango yield
with an average of 186.10 and 162.63
kg/tree during the two successive
seasons, respectively. Furthermore, the
percentages of infestation incidence
during April peak was highest effective
causing the greatest loss in mango yield
with an average of -32.93 and -12.16%
during the two successive seasons
respectively. But, the peak of infestation
incidence in November was the lowest
effective causing the least percentages of
27
reduction in mango yield with an average
of -98.95 and -131.30% during the two
successive seasons respectively (Table
10). Generally, it seems that the
population density and infestation
incidence by
A. tubercularis
during April
peak was the most serious one, during
the two seasons, causing the greatest loss
in mango yield which that coincided with
the newly spring growth cycle for the
vegetative growth of mango trees. These
results were confirmed by the findings of
El-Said (2006) who found that the high
infestation levels, the feeding of this pest
caused a serious damage resulting in
early leaves drop and yield reduction.
Bakry (2009) reported that the early
season infestation with the Maskell scale
insect,
Insul
a
spis pallidula
during May
was more effective than other months
causing the greatest loss in mango yield.
Also, Salman and Bakry (2012) stated
that the early infestation with the
mealybug,
Icerya Seychellarum
during
May was more effective than other
months causing the greatest loss in
mango yield. Bakry and Mohamed
(2015) reported that the infestation by
Aonidiella aurantii
(Mask.) during April
was more effective than other time
causing the greatest loss in mango yield.
Generally, it could be concluded that the
reduction in mango yield was considered
as a summation of different factors
including level and time of infestation
and the ability of variety to infestation.
These results are similar to those
obtained by Reddy-Seshu (1992) who
found a linear relationship between
infestation and yield loss, and more
increasing in yield loss as a result of the
earlier infestation. Also, Selim (2002)
studied the effect of Maskell scale insect,
Insulaspis pallidula
(Green) infestation
on the yield of mango trees. He stated
that the yield decreased gradually with
increasing the population density of this
pest. He added that the yield decreased
gradually with increasing the population
density of
Insulaspis pallidula
(Green) in
four peaks (September, April, July and
August).
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