トビイロウンカにおける長翅型, 短翅型の決定時期について : ウンカ類の翅型に関する研究IV

抄録

Rearing experiments were undertaken to find the stages susceptible to effect the crowding to produce the two wing-forms, the brachypterous form and the macropterous form, in the brown planthopper, Nilaparvata lugens STAL. As shown in Fig. 1,the brachypterous female and the macropterous male are obtainable at a density of 1(number of larvae per rearing tube, 2 cm in diameter and 17.5 cm in length), the brachypterous female and male are characteristic at a density of 5,though not so high percentage in the latter, and the macropterous female and male are obtained at a density of 20(KISIMOTO, 1956). Therefore, the larvae were transferred between two rearing densities of the three at various stages to find the stages susceptible to the effect of crowding. The results are shown in Fig. 2. 1. In the female, high densities during the 2nd to the 4th larval stage induce the appearance of the macropterous form and low densities induce that of the brachypterous form. 2. In the male, high percentages of the brachypterous form are produced among the larvae reared at a density of 5 during the 1st to the 3rd larval stage, and a few brachypterous forms are also produced at a density of 20 during the 1st to the 2nd stage. The susceptible stages to effect the crowding are localized a little earlier than those of the female. From this result the presence of the optimum density for the appearance of the brachypterous male which was proposed by the author in the previous paper (KISIMOTO, 1956)is proved. 3. The 3rd larval stage is most sensitive to the effect of density determining the wing-form in both sexes and the effect during the 1st, 2nd and the 4th larval stages modifies that of the 3rd stage. The 5th stage is considered to occur almost after the determination. 4. In the experiments in which the larvae were transferred between densities of 1 and 5,the macropterous and he brachypterous forms were produced in both sexes in various percentages. The brachypterous male presents the highest developmental speed, the macropterous female the lowest and the macropterous male and the brachypterous female are intermediate. It is interesting that this divergent occurrence of the wing-form was induced without accompanying any considerable change of the average developmental speed of the whole members. This divergence may be considered to be an adaptive character of the population.