ヤノネカイガラムシ第1世代幼虫の発生型,特にその双峰型が生ずる原因について

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  • On the Type of Appearance of the Arrow-head Scale Larva in the First Generation, with Special Reference to Reason Why Two Peaks Appear
  • ヤノネカイガラムシ ダイ1 セダイ ヨウチュウ ノ ハッセイガタ

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It has been known that the appearance of the first generation larva of the arrow-head scale, Unaspis yanonensis KUANA shows two prominent peaks of appearance under the natural condition. It may be an important problem to clarify the mechanism of such unusual occurrence of the larva, from the view point of the control of this insect.<br>In order to make clear reason why the fluctuation curve of the larval appearance in the first generation is divided into two parts, the following investigations were carried out from 1961 to 1962.<br>The results are summarised as follows:<br>1. The leaves on which arrow-head scales live, were collected periodically, and the stage in which the insect hibernates was ascertained. From the results, it was found that the scale insect hibernates only in the adult stage of the female. According to the investigation on the degree of maturity during the hibernating period, about 80 per cent of the adults were matured and the others were inmature. Although the time of appearance of the larvae derived from these inmature adults was almost equal to that from matured, the number of larvae occurred from the former was extremely small compared with the latter.<br>2. From the observation it was ascertained that the appearance of larvae was initiated, with a few exceptions in middle of May; and the peak of first larval appearance came at the end of May. At the beginning of June the scale insect ceased to produce larvae for about 9 days and after this resting period it commenced to produce larvae again making second peak of appearance.<br>3. In order to make clear the cause that the larval appearance stops once in the first generation period, the ovary of the adult insect reared on the orange fruit at 25°C was examined at regular intervals.<br>From the results, it was ascertained that the arrow-head scale has the ovovipiparous characteristic and the egg stays in the ovary until the embryonic development is almost completed. Further, it may be interesting that the ovary ceases to produce eggs when they reach maximum number and it becomes active in egg production again when the egg-laying is initiated.<br>4. It seems probable that the occurrence of two peaks of larval appearance in the first generation is due to the resting period observed in the process of egg production in the ovary.

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