Abstract
To search for the factors of producing hypopus in grain mites, the author observed changes of population and age composition in Lardoglyphus konoi through breeding experiments under different relative humidities on the following series of diets. About 300 mites were inoculated on 10g of diets composed of dried fish meal powder (niboshi) at the ratio of 10 : 0, 8 : 2, 6 : 4, 4 : 6, 2 : 8, 0 : 10 respectively, and each of these series was kept under the relative humidities 64%, 75%, 85%, and 94%, in an incubator at 25℃. At 94% R. H., slight reproduction occurred in 2 weeks but diminished till following week. In each series, the highest count of mites was observed under 85% R. H., but the longevity did not last for 5 weeks. The highest count of all the cases, 1640 individuals per 0.5g, was seen on 0 : 10 fish meal diet at 4 weeks under 85% R. H. The time to reach the highest count became shorter in accordance with the ratio of fish meal in diets increased. The period of existence was longest at 75% R. H. that lasted for 11 weeks especially on 6 : 4 and 4 : 6 fish meal diets. At 64% R. H. the mites could not survive. As for the age composition the following three phases were distinguished : Growing phase, in which the population in larval stage was highest, stable phase, the population in each stage appeared on the average and senile phase, the population in adult was highest. The age composition under 75% R. H. which showed either growing or stable phase in process of increase turned gradually into senile phase, and diminished after the climax. As to the 6 : 4 and 4 : 6 fish meal diets, the senile phase after the climax changed once into growing phase in 9 weeks and into senile again the following week. Under 85% R. H., change of the age composition took two types according to the diets : growing phase at 2 weeks, senile at 3 weeks and stable at 4 weeks on 10 : 0 to 4 : 6 fish meal diets, whereas on 2 : 8 and 0 : 10 fish meal diets growing and senile phase respectively at 2 weeks, both senile at 3 weeks and both growing again at 4 weeks. The hypopus appeared in 10% after 4 weeks on 2 : 8 fish meal diet under 75% R. H., while they were scarcely found under the other relative humidities in this experiments.
