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Annals of Biological Research, 2014, 5 (2):111-116
(http://scholarsresearchlibrary.com/archive.html)
ISSN 0976-1233
CODEN (USA): ABRNBW
Sex ratios of Brontispa longissima (Gestro) infesting coconuts in selected
provinces in the Philippines
Ana Marie T. Acevedo1, Mark Anthony J. Torres2, Muhmin Michael E. Manting2, Emma
Sabado3, Ambrosio Raul Ricardo Alfiler4 and Cesar G. Demayo2
1
Surigao del Sur State University- Cantilan Campus
Department of Biology, MSU-Iligan Institute of Technology, Iligan City,
3
MSU-Marawi,
4
Epidemiology – Entomology Division, Albay Research Center, Philippine Coconut Authority,
Banao, Guinobatan, Albay
2.
_____________________________________________________________________________________________
ABSTRACT
This study was conducted to describe populations based on sex ratios of adult Brontispa longissima (Gestro) from
selected areas in Luzon, Visayas and Mindanao, Philippines. G-test for goodness of fit was employed to determine if
each population follow the expected 1:1 ratio. While the results of the survey showed that some populations did not
deviate from the expected 1:1 sex ratio, several male-biased and female-biased ratios were also observed. The
deviations were hypothesized to be due to factors which are both genetic and environmental in nature.
Keywords: adult sex ratio, male-biased, female-biased sex ratio, intrinsic and extrinsic factors
_____________________________________________________________________________________________
INTRODUCTION
The coconut leaf beetle (Brontispa longissima), is one of the most damaging pests of coconut and other palms
multiply in exponentially resulting to outbreaks in coconut plantations. Both larvae and adults feed on the soft
tissues of young unfolded coconut leaflets which later become brown, dry and die [1, 2]. The beetles attack all ages
of coconuts, severe damage is between four to five years old [3]. Outbreaks of this species of insect in the
Philippines can be considered temporally rare events since the insect can be found in many places where coconuts
are planted but do not cause threats since only certain trees are feed upon and the population is kept at low level.
Temporal outbreaks of many insect pest species have aroused the interest of many theoretical and applied
entomologist alike looking into possible reasons for their dynamics, their unique adaptations, density dependence,
life tables, stability and diversity. Numerous hypotheses are proposed – changes in physical environment such as
changes in weather, genetic makeup, intrinsic life history characteristics, interactions with higher or lower trophic
levels; changes in host plant physiology or biochemistry as a result of environmental stresses; and escape
from regulation by natural enemies [4, 5]. In this study, we made a survey of B. longissima to understand some
aspects of its biology such as sex ratio. Since sex ratios can influence population dynamics, outbreak/epidemics, it is
important to know the sex ratios of these insect pest. The sex ratio in diploid population plays a key role in
population dynamics by determining gene mixing levels [6] and reproductive strategies [7]. Population status of
pests requires effective population size which is strongly influenced by sex ratio [8, 9] thus is conducted in this
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study. Adult sex ratios (ASRs) and population size are two of the most fundamental parameters in population
biology as they are the main determinants of genetic and demographic viability, and vulnerability of a population to
stochastic events [10].
MATERIALS AND METHODS
Qualitative and quantitative descriptions on the degree of damage on coconut trees
Coconut plants were assessed to describe the extent of damage on the young leaves of the sampled coconut trees (46 yrs. old). Numerical values were assigned: 1- light moderate damage (1-2 young leaves colored brown); 2moderately damage (3-4 young leaves colored brown); 3-heavy/severely damage (the infestation resulted in the
complete defoliation of the leaves or dying of leaves) [11].
Collection of Samples and Sampling Sites
Opportunistic sampling was done in the collection of adult B. longissima (Gestro). Insects were randomly collected
in affected coconut trees in selected villages/towns in the provinces of the Philippines. The areas were: Banao in
Guinobatan, Albay; Plaridel, Baybay, Leyte; Poblacion in Albuera, Leyte; Cambalatong in Albuera, Leyte; Tandag
City, Surigao del Sur; MSU in Marawi City, Dimalna in Marawi City; Wao, Bayang, Bubong in Lanao del Sur;
Sapad, Walou Datu in Lanao del Norte; Parang in Maguindanao; Aurora, Dumalinao, Malangas in Zamboanga del
Sur, Pagadian City; Napolan, Pagadian City; CMU, Musuan, Bukidnon; San Vicente, Butuan City, Trento, Agusan
del Sur and Sibutad, Zamboanga del Norte (Figure 1).
Those samples in Banao, Guinobatan, Albay (Luzon), Albuera and Baybay Leyte (Visayas) and in Tandag City,
Surigao del Sur (Mindanao) were randomly collected in slightly, moderately and heavily infested coconut trees
identified by the Philippine Coconut Authority.
The collected samples were placed in plastic containers containing prepared fixative (70% ethyl alcohol + 30%
glacial acetic acid) for preservation. Sexes were determined (Ayri & Ramamurthy, 2012) in the laboratory using
Lyka Dissecting Microscope and photograph using GE digital camera. Simple counting of male and female was
done per tree per sampling site.
G test for goodness of fit was employed to determine if the observed values deviate with the biological expected
ratio of 1male is to 1 female per provinces and per tree per sampling site.
RESULTS AND DISCUSSION
Fourteen out of the twenty-five populations collected from different provinces in the Philippines were observed to
have statistically deviated from the expected 1:1 sex ratio (Table 1). Eleven of these populations are biased towards
the male sex, four were female-biased and the other eleven populations did not deviate from the expected 1:1 sex
ratio. Based on the degree of damage, no deviation from the sex ratio was observed except for moderately damaged
plants in Tandag, Surigao del Sur (Table 2). It is important to note here that the pooled Plaridel and Tandag
populations have female-biased sex ratio but when the analysis was made based on the degree of damage, no
deviation was observed from the expected 1:1 ratio except when the analysis was done per tree basis (Table 3)
where there are some trees showing female-biased sex ratio.
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Figure 1. Map of Philippine Island showing the locations of the sampling sites.
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Table 1 Sex ratio of adult B. logissima collected from selected provinces in the Philippines.
Provinces
Banao, Guinobatan, Albay
Plaridel, Baybay, Leyte
Poblacion, Albuera, Leyte
Cambalatong Albuera, Leyte
Tandag, Surigao del Sur
MSU, Marawi City 1
Dimalna, Marawi City
MSU, Marawi City 2
Wao, Lanao del Sur 1
Wao, Lanao del Sur 2
Wao, Lanao del Sur 3
Bayang, Lanao del Sur
Bubong, Lanao del Sur
Sapad, Lanao del Norte
Walu a Datu, Lanao del Norte
Parang, Maguindanao
Aurora, Zamboanga del Sur
Dumalinao, Zamboanga del Sur
Malangas, Zamboanga del Sur
Pagadian City
Napolan, Pagadian City
CMU, Musuan, Bukidnon
San Vicente, Butuan City
Trento, Agusan del Sur
Sibutad, Zamboanga del Norte
No. of Male
170
33
39
48
17
105
30
212
159
108
30
30
10
57
131
85
210
12
30
74
169
79
181
56
30
No. of Female
203
78
58
43
58
85
28
62
85
59
51
18
4
30
21
103
121
8
30
31
48
30
36
42
55
G-value
2.749
17.93
3.36
0.176
22.481
1.903
0.017
85.583
22.178
13.993
4.99
2.543
1.826
7.89
86.812
1.539
23.679
0.452
2.017
17.279
70.239
21.88
104.213
1.73
6.87
P-value
0.097
0.00023*
0.067
0.675
2.12E-6*
0.168
0.896
2.22E-20*
2.48E-6*
0.000183*
0.025*
0.111
0.177
0.004971*
1.19E-20*
0.215
1.14E-6*
0.502
0.156
0.000032*
5.25E-17*
2.90E-6*
1.82E-24*
0.188
0.008768*
Table 2. Number of male and female adult B. longissima collected from slightly, moderately and heavily infested coconuts.
Degree of Infestation
Slightly Infested
Moderately Infested
Heavily Infested
Slightly Infested
Moderately Infested
Heavily Infested
Slightly Infested
Moderately Infested
Heavily Infested
Banao, Guinobatan, Albay
No. of Male (mean) No. of Female (mean)
4
5.25
3.33
4
29.8
34
Plaridel, Baybay and Albuera, Leyte
5.11
4.77
4.33
6.22
5.5
12.66
Tandag, Surigao del Sur
8
10
4
12
2.5
10
G Value
0.169
0.182
0.277
P value
0.681
0.67
0.599
0.012
0.34
2.901
0.941
0.56
0.089
0.223
4.186
4.819
0.637
0.041*
0.28
It was hypothesized that in natural populations of B. longissima, a 1:1 sex ratio is always expected because of strong
frequency-dependent selection on the production of male and female offspring [12]. However, the population sex
ratios observed in the different geographical populations show otherwise. Variability in sex ratios were observed.
Several studies conducted on primary sex ratio of selected species in laboratory condition did not follow Fisher’s
principle [13-22]. There are also many examples of biased sex ratios that have been observed in nature, providing
new dimensions to Fisher’s central theory rather than invalidating it [23]. It is argued that biases in relative
frequency of sexes in animal populations may occur at several temporal levels; at conception (primary sex ratio), at
adult emergence (secondary sex ratio), and after the emergence of adult (tertiary sex ratio) [24]. Biases in sex ratio
may have affected the viability of some populations and may arise for different reasons, such as biased primary ratio
and differential juvenile or adult mortality of sexes [25]. The biased sex ratios observed in this study in some
populations of the insect pest can be due to non-random harvest as a consequence of, for example, sex differences in
behavior, size, or morphology, or simply as a consequence of hunter preferences [26-28]. Sex ratios can also be
influenced by environmental changes such as, for example, changes in the temperature regime that may cause sexspecific mortality or growth. Although not determined in this study, observations show the different geographical
locations where the insects were collected have different topographies and elevation and have differed temperatures
and may have directly influenced the production of males and females as shown in some studies in species with
environmental sex determination [29, 30], or in species where the genetically determined sex can be reversed during
a critical period in life. Environmental sex reversal has been observed in several species of fish and amphibians [31-
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34] but it still to be investigated in B. longissima. To be able to assess the impacts of biased sex ratios in the
management of this insect pest, more studies will have to be conducted taking into consideration the effects of both
intrinsic and extrinsic factors affecting sex ratios in the population of this pest. For example, the sampling sites that
were managed by the Philippine Coconut authority (PCA) such as in Albay are applying multiple strategies to
control the spread of B. longissima in the neighbouring farms such as mechanical (pruning, cutting), chemical (use
of pesticides such as methidathion, actara and prevathon) and biological control (use of parasitoids, Tristraticus sp.
and Asecodes hispinarum, fungus Metarrhizium anisphae). Collections of individuals of the insect pest in this
managed area showed non-significant deviation from the 1:1 ratio but in non-managed areas, both male and femalebiased ratios were observed. Correlating these results with the degree of infestation of coconut trees should be
further explored in order to come up with the best pest management strategy for this pest.
Table 5. Number of male and female adult B. longissima observed per coconut tree.
Banao, Guinobatan, Albay
No. of Male
No. of Female
G Value
P value
3
2
0.201
0.654
11
14
0.361
0.548
1
4
1.927
0.165
1
1
0.00E0
1
4
5
0.111
0.739
2
2
0.00E0
1
4
5
0.111
0.739
3
6
1.019
0.313
6
15
3.985
0.046*
55
59
0.14
0.708
80
80
0.00E0
1
5
10
1.699
0.192
Plaridel, Baybay and Albuera, Leyte
1
7
11
0.896
0.344
2
1
4
1.927
0.165
3
5
18
7.8
0.005225*
4
14
31
6.584
0.01*
5
5
10
1.699
0.192
6
1
2
0.34
0.56
7
20
22
0.095
0.758
8
6
6
0.00E0
1
9
6
12
2.039
0.153
10
1
1
0.00E0
1
11
3
7
1.646
0.2
12
2
2
0.00E0
1
13
0
1
1.386
0.239
14
1
4
1.927
0.165
15
0
1
1.386
0.239
16
20
10
3.398
0.065
17
1
1
0.00E0
1
18
1
5
2.911
0.088
19
1
3
1.046
0.306
20
2
5
1.328
0.249
21
1
2
0.34
0.56
22
5
6
0.091
0.765
23
6
5
0.091
0.765
24
9
6
0.604
0.437
Tandag, Surigao del Sur
Tree Number
No. of Male
No. of Female G Value
P value
1
8
10
0.223
0.637
2
6
10
1.011
0.315
3
2
14
10.124
0.001463*
4
1
14
13.447
0.000245*
5
4
6
0.403
0.526
Tree Number
1
2
3
4
5
6
7
8
9
10
11
12
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CONCLUSION
Variability in sex ratios was observed in twenty-four populations of B. longissima where sex-bias was documented.
The deviations from the 1:1 ratio was hypothesized to be a consequence of a lot of factors including genetics and
environmental in nature. The differences in population sex ratios may have an implication in the management of this
pest. However, a thorough study correlating the deviations from the 1:1 ratio with intrinsic and extrinsic factors and
with various pest management programs should be further explored.
Aknowledgement
The main author would like to thank CHED-FDP-II and Surigao del Sur State University for the scholarship grant,
Philippine Coconut Authority (PCARC) in Banao, Guinobatan Albay especially to Mateo B. Zipagan, Jun, Lito and
Mel, PCDM in NW Leyte, Joel O. Pilapil, Dan Dacera and Danny Ramos, PCA Tandag City, Surigao del Sur,
Lyndon and Jacky of the department of agriculture (DA).
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