Available online at www.scholarsresearchlibrary.com Scholars Research Library 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 111 Scholars Research Library Ana Marie T. Acevedo et al Annals of Biological Research, 2014, 5 (2):111-116 ______________________________________________________________________________ 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. 112 Scholars Research Library Ana Marie T. Acevedo et al Annals of Biological Research, 2014, 5 (2):111-116 ______________________________________________________________________________ Figure 1. Map of Philippine Island showing the locations of the sampling sites. 113 Scholars Research Library Ana Marie T. Acevedo et al Annals of Biological Research, 2014, 5 (2):111-116 ______________________________________________________________________________ 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- 114 Scholars Research Library Ana Marie T. Acevedo et al Annals of Biological Research, 2014, 5 (2):111-116 ______________________________________________________________________________ 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 12 115 Scholars Research Library Ana Marie T. Acevedo et al Annals of Biological Research, 2014, 5 (2):111-116 ______________________________________________________________________________ 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. 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