The physical Ecology of Microplectron fuscipennis, Zett. (Hym. Chalc.)

Abstract

1. The influence of atmospheric humidity on the various stages in the life-cycle of Microplectron fuscipennis, Zett., is examined. Both the longevity of the adults and the extent of oviposition are found to be proportional to the saturation deficiency of the atmosphere. Under favourable temperature conditions, functional activities are at their maximum in a moist climate, but a wide tolerance is exhibited so far as oviposition is concerned. At normal humidities no effect on the developmental period of the parasite is apparent when the humidity is varied, and this is shown to be due to the protection afforded by the host cocoon.2. Temperature affects the parasite in a normal manner. The threshold of development is approximately at 8·3°C., and the zone of functional activity is from 15° to a little over 35°C. Optimum conditions for oviposition and development occur between 20° and 35°C. Death occurs at 40°C., while at the lower temperatures, near freezing point, starvation of adults takes place after a lengthy exposure. The hibernating parasite can withstand temperatures very much below freezing point, field records coming from countries where the winter temperature falls to so little as −37°C.3. The relation of Microplectron to climate is discussed and an explanation is offered of the wide variation in natural parasitism occurring in European countries.4. The actual and possible distributions of the parasite in Europe are discussed and a map is presented depicting the position as known at present.5. The possible distribution of the parasite in North America, after liberations have been made, is dealt with and it is shown that the present trend of dispersal of Diprion polytomum is in the direction of climatic conditions that are more favourable to the parasite than are those in the area where the parasite has already become established.