Production Study of the Population of the Pine Caterpillar (Dendrolimus spectabilis Butler)

Abstract

マツカレハ幼虫個体群の生産を, 苗圃の実験個体群について調べた。幼虫の密度推定は糞数法および直接観察によって行なった。幼虫1個体当りの食物消費量, 同化量, 呼吸量, 生長量は実験室において飼育個体を用いて測定した。個体群の食物消費量, 同化量, 呼吸量, 生長量は飼育個体の各量と個体数変動とから測定した。一頭の幼虫は一生育期間に平均約14. 0g (乾重) のクロマツの葉を消費した。そのうち11. 2gは排出され, 2. 8gが同化された。同化量は80％すなわち2. 3gが呼吸として消費され, 生長量は0. 5gであった。幼虫の密度は, 実験開始時の1967年9月には63頭/m_2であったが, 蛹化時の1968年7月には6頭/m_2にまで減少した。個体群としては一生育期間に133g/m_2のクロマツの葉を摂食した。そのうち106gは糞として林床に落下し, 27gが個体群によって同化された。同化量のうち21gは呼吸として消費され, 個体群の生長量は6gであった。個体群の生長量と個体群の現存量との間には正の相関が認められた。個体群の積算摂食量と個体群現存量との間にも正の相関が認められた。

Productivity of a pine caterpillar population was investigated in the present study. The changes in larval density of the pine caterpillar population were estimated by the fecal-pellets counting method and by the direct counting method at a pine stand in a nursery. The food consumption, assimilation, respiration and growth were also measured in the laboratory. The total food consumption, assimilation, respiration and growth of the population were calculated utilizing the individual values and population density. An individual larva consumed about 14.0g of pine needles over one growing season. From which 11.2g was defecated as feces, and the rest 2.8g was assimilated. 2.3g, or eighty per cent of the assimilated matter was used for respiration and 0.5g was used for growth of larval body weight. Larval density was estimated at about 63 individuals per square meter in September 1967, which decreased to about 6 individuals per square meter in July 1968 (at the time of pupation). The total food consumption of the larval population over one growing season was estimated at 133g/m2/year. From this 133g, 106g fell as feces and 27g were assimilated by the population. 21g, or eighty per cent of the assimilated matter was used as respiration and 6g was used for population growth. Positive correlation was observed between population growth and biomass of larval population. Food consumption of a population also positively correlated with the biomass.