THE MORPHOMETRY AND SEX RATIO OF Gerris marginatus Say (HETEROPTERA: GERRIDAE) IN TROPICAL AREA

Abstract

Gerris marginatus is one fresh water insect distributed from temperate to tropical
areas. It can be found in almost every freshwater biotope, making them excellent objects for
ecological and biogeographic studies.  Most recent studies found that this water insect was
one good candidate for examining the effect of fresh water pollution.  This species shows
morphometric differences between male and female, but there has no studies examining this
morphometric differences particularly in tropical areas.  This study aimed to determine and
investigate the morphometric differences between male and female and their sex ratio of G.
marginatus in one of freshwater body in Bali.   Samples were collected from Jangu River at
Karangasem Regency on February 2014.  Samples were preserved in 70 % awaiting for
identification and further studies. Identification was performed at Animal Taxonomy
Laboratory, Biology Department. The results show that there were morphometric differences
between male and female of G. marginatus in tropical area.  Males were significantly larger
of many variable measured compared to females. However, they also exhibit sex ratio bias
toward females.