摘要:

This first in a series of five papers includes a review of the literature on diapause and an outline of the life cycle of the European spruce sawfly in Canada, especially the developmental stages within the cocoon. In studies of factors influencing the inception of diapause, evidence has been secured from offspring of stock from one-generation and two-generation areas that there are genetic differences within the species with respect to the capacity for development without diapause. Environmental factors are capable of bringing on diapause, and such factors are obviously operative during the development of the last seasonal generation of "emergent" field populations. However, analysis of weather conditions and incidence of diapause in such field populations failed to indicate correlation between the degree of diapause and any one environmental factor.

ISSN:1923-4287    

DOI:10.1139/cjr41d-027

出版商:NRC Research Press    

年代:1941

数据来源: NRC

摘要:

Field and laboratory experiments have shown the importance of a period of "cold-rest" at a temperature below the threshold of development as a requirement for overcoming diapause in the spruce sawfly, especially in stock from a one-generation area. After cold-rest, maximal development results at a temperature of 74° to 75° F. or higher, and after contact with water. Temperatures in the field are lower and fail to promote so high development as may be obtained in the laboratory; however, temperature variations between 65° and 45° F. evidently have little influence on the degree of emergence from the diapause condition, though speed of development is directly affected. The benefit of contact with water is reduced or lost if contact occurs only while soil temperature remains below the threshold of development, and if the moisture taken up in the cocoon wall is lost by evaporation before it can be absorbed by the larva. The role of the cocoon in water exchanges, and differential effects of abnormal weather conditions upon intracocoon development in stocks in one-generation and two-generation areas, are described.

ISSN:1923-4287    

DOI:10.1139/cjr41d-028

出版商:NRC Research Press    

年代:1941

数据来源: NRC