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 111 Scholars Research Library Sex ratios of Brontispa longissima (Gestro) infesting coconuts in selected provinces in the Philippines Ana Marie T. Acevedo 1 , Mark Anthony J. Torres 2 , Muhmin Michael E. Manting 2 , Emma Sabado 3 , Ambrosio Raul Ricardo Alfiler 4 and Cesar G. Demayo 2 1 Surigao del Sur State University- Cantilan Campus 2. 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 _____________________________________________________________________________________________ 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