BIO-ECONOMICS OF SOME LARVAL POPULATIONS OF PLEUROSTICT SCARABAEIDAE ON THE FLOOD PLAIN OF THE RIVER TAMAGAWA

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This paper deals with the bio-economy of the larval populations of pleurostict Scarabaeidae. The field surveys were carried out to see the population dynamics during the periods from July 1956 to July 1957 and from Nov. 1957 to Nov. 1958 on the flood plain of the River Tamagawa near Tokyo. On the other hand, several representative species were reared on quartz sand and soils in the laboratory, and fed on dried leaves of Shiia sieboldi and Miscanthus geniculatus to determine the amounts of such bioeconomic items as ingestion, defecation, assimilation, respiration and growth. Computations of population metabolism were made based on the above two series of data. The quantitative relations obtained for population metabolism of the main species Anomala orientalis are as follows. The amount of matters ingested per square meter per year was equivalent to 1700 Cal or about 300g in dry weight of plant leaves and that defecated was 832 Cal or 164g in dry weight, and the body materials of the larvae produced (growth or net production) was 65 Cal or 52g in live weight. The larvae were reared at constant 20℃, 25℃, 30℃ and at room temperature. At 30℃ the growth rate was the largest and the length of the larval stage was the least of the above four. The larvae fed on the dried leaves of the grass, M. geniculatus, grew faster than those fed on the leaves of the evergreen forest tree S. sieboldi. The meaning of the difference of food substance and that of habitat are discussed. Comparisons were made on the metabolism of the larval population of Scarabaeidae and that of Pieris rapae with reference to the difference of the habitat and the life type.