This study was conducted to investigate the impacts of male incubating behaviour on hatching rate of giant water bug from May 2, 2011 to September 2, 2012 in the laboratory(24.1±0.2℃) in HECRI. The giant water bug, Lethocerus deyrollei, is the largest aquatic insect in Korea (length, Female: 63.5±0.4mm, Male: 54.0±0.3mm). L. deyrollei has been designated as an endangered species by the Ministry of Environment of Korea since 1997. L. deyrollei lay eggs as clusters on stems or vegetation of aquatic plants above the water. Males do not leave the stems which eggs are sticked until eggs hatched because they protect eggs against predators and supply water to eggs. The incubating behavior of male L. deyrollei was observed three times a day, 06:00, 13:00 and 19:00 respectively and 32 egg-clusters were used. Three treatment - presence of male incubation, absence of male incubation, and artificial removing male - were manipulated to observe the hatching rate of egg masses. There were different hatching rates between presence (67.2%) and absence (1.9%) of male incubatng behavior. In case of artificial removing male, eggs could not hatch. The mean diameter of eggs(2.87±0.03mm) which male incubated was bigger than that of eggs(2.18±0.03mm) which male did not care.

This study was conducted to distinguish adult morphology of the giant water bug (Lethocerus deyrollei) between over-wintered (OLD) and new-born (NEW) populations using materials collected from Gyodong island in Gyeonggi-do, Korea, as well as individuals reared in the laboratory (LAB population) as a control. As a result, no fundamental differences were found in external body structure between OLD, NEW, and LAB populations. However, marginal area of basal procoxa in ventral prothorax and jointed part of forefemur and foretibia were greatly worn in the OLD population. Mid-claws were shorter than 0.5 times the length of the 2nd mid-tarsus, the membranous margin of hemelytra was greatly worn, and hairs of the 5th abdominal tergum were greatly reduced in the OLD population.