Consumption and food utilization by individual larvae and the population of a wood borer Phymatodes maaki Kraatz (Coleoptera: Cerambycidae)

The consumption and the utilization of food by the individuals and the population of a wood borer, Phymatodes maaki Kraatz feeding on the dead wood of a Japanese wild vine, Vitis coignetiae Pulliat were studied at Mt. Daibosatsu, Yamanashi Pref., central Honshu from 1974 to 1976. As for individuals of P. maaki, the estimates of the ratio of growth to consumption and that of assimilation to consumption were very low, amounting to 1.24 and 3.23% in dry weight, 1.23 and 3.12% in carbon weight, and 16 and 13.6% in nitrogen weight respectively. The ratio of growth to assimilation was estimated at 35% in dry weight, 39% in carbon weight and 118% in nitrogen weight. Dry body weight of the adult was correlated with the amount of consumption of the larva. The parasitism by two Ichneumonidae species seemed to be the main mortality factor of the population of P. maaki. A minimum estimate of mortality from egg stage till emergence was 75%. As for the bioeconomy of the population, waste consumption i.e. the consumption of individuals that died before emergence amounted to 75% of total consumption. The growth efficiency (biomass of adults/total consumption) was 0.24% in dry weight, 0.26% in carbon weight and 3.4% in nitrogen weight. The waste efficiency (waste consumption/biomass of adults) was 310 in dry weight, 285 in carbon weight and 22 in nitrogen weight. Approximately 18% of the dead wood of V. coignetiae was decomposed by the feeding of the population. The dry weight of an adult was inversely correlated with density of larvae in the dead wood from which it emerged, but not significantly correlated with the diameter of the wood. The ratio of adult emergence i.e. the survival rate was inversely correlated with density of larvae, but the mortality by parasitism was not density dependent. This seems to suggest that there was an intraspecific competition for the limited food.