Territorial behaviour in the genus Megalagrion (McLachlan) (Zygoptera: Coenagrionidae)

Preliminary observations were made on the territorial behaviour of 9 taxa of Megalagrion in the Hawaiian Islands, July — August 1982. M. vagabundum and M. oresitrophum, which breed in small streams, showed typical territorial behaviour: highest steady densities of 50 and 38 males per 100 m of water edge were recorded respectively. M. hawaiiense (Maui form) and M. pacificum are probably also territorial as may be M. blackburni. M. heterogamias and M. nigrohamatum, which spend much time perched on rocks in larger streams, showed aggressive behaviour but were either very weakly territorial or not at all. The form of M. hawaiiense in Hawaii, whose larva is probably semi-terrestrial, also appears to be non-territorial, M. amaurodytum peles appears not to defend the Astelia plants in which eggs are laid and in whose leaf axils the larvae develop. The size of territories in endemic Hawaiian Odonata appear to be proportional to size of insect.