Daily food consumption of Mnais pruinosa Selys (Zygoptera: Calopterygidae)

Field observations were carried out at a mountain stream, some 18 km NE of Fukuoka City, Japan. The food consumption was estimated by computer simulation using the daily frequency of feeding flights and the mean weight of preyinsects collected by sticky traps. The estimates of food consumption on May 16 and 19 were 4.61 mg (min. 3.30, max. 7.67) and 5.38 mg (min. 3.61, max. 7.04) respectively. The ratios of these values to body weight amounted to 9,7% and 11.4% respectively. In addition, the daily change in stomach contents and the instantaneous rate of food output from the stomach were examined for estimating food consumption. Daily food consumption in Sympetrum frequens, Calopteryx cornelia and M. pruinusa was compared and a discussion is presented on the functions of the dragonfly territory, particularly on the function of the "prevention of food shortage".