220 EXPERIMENTAL FA1HIS 



2 GEORGE V., A. 1912 



ing larvae in the nests. It was found that the larvae in rather small nests were killed 

 Ly exposure for a short time to a temperature of — 30 degrees C. (equals — 22 degrees 

 F.) In larger nests containing about 120 to 350 larva?, all the larvae were killed with a 

 minimum temperature of — 35 degrees C. (equals — 31 degrees F.). Many of the winter 

 webs found in Nova Scotia are considerably larger than those used by Grevillius in his 

 experiments and a much lower temperature would, therefore, be needed to kill all the 

 larvae contained in such large nests. Sanderson* has studied the effects of a low tem- 

 perature on the mortality of the larvae of the Brown-tail Moth in Maine and New 

 Hampshire. He found that in the case of average-sized nests containing 300 or 400 

 larva?, 72 per cent to 100 per cent of the larvae were killed by a minimum temperature 

 of — 21 degrees F. or lower, a less percentage being killed in the case of larger nests. 

 Grevillius records the interesting fact that at Ivasan, which is the northern limit of 

 the Brown-tail Moth in Russia, the mean annual minimum temperature is about — 20 

 degrees F. which is practically the same temperature as that which his experiments 

 indicated as being the lowest at which the larvae could exist. 



Although these experiments and observations would appear to indicate the possi- 

 bility of predicting the approximate distribution of the Brown-tail Moth in eastern 

 Canada, there are other factors governing the distribution which prevent the attain- 

 ment of positive conclusions from a study of the minimum isotherms alone. 



THE GIPSY MOTH (Porthetria dispar L.) 



This insect has not yet reached Canada, but as it is spreading northward through 

 the State of Maine and is slowly approaching the frontier, it is of the greatest import- 

 ance that its appearance in the various stages should be known in Canada. It is liable 

 to be carried in many ways. The caterpillars may the transported on freight and 

 other goods shipped into Canada by railroad or boat from the infested region which is 

 shown in the accompanying map. They are also carried on vehicles. The egg masses 

 also may be transported on goods, especially on lumber. The various stages in the life- 

 history of the insect are illustrated herewith. (This illustration is from one published 

 and distributed by the State Forester of Massachusetts). 



The eggs are deposited in yellowish or light-brown felt-like masses which are about 

 three-quarters of an inch long. They are usually deposited on the trunks of the trees 

 and in crevices, but they may also be found in all kinds of situations: on buildings, 

 on fences and hrmber, in boxes and among rubbish. The eggs hatch about the begin- 

 ning of May and the caterpillars immediately begin to feed. They feed on the foliage 

 of practically all trees, orchard, shade and forest trees and shrubs. As defoliating 

 insects they are more serious than the Brown-tail Moth owing to the fact that they 

 strip coniferous trees which are killed by repeated defoliation. They will also attack 

 garden and field crops and even grass. As the caterpillars become larger they feed at 

 night, hiding in clusters during the day in crevices, etc. By the beginning of July 

 the caterpillars are usually full-grown. The full-grown caterpillar is from two to 

 three inches in length, dark-brown or greyish in colour with two rows (four pairs) 

 of blue spots succeeded by two rows (six pairs) of red spots along the back. The body 

 is provided with tufts of long hairs. They pupate in those situations in which the egg 

 masses are found and also in the foliage. 



The moths emerge about the end of July or beginning of August, according to 

 the locality and season. The male moth is yellowish brown or light brown in colour, 

 having the fore wings banded with wavy darker brown bauds, as shown in the illus- 

 tration. It measures about one and a half inches across the wings. The antenna? are 

 feather-like. The female moth is almost white in colour. The fore wings are banded 

 with four wavy dark lines and there is a series of black dots around the outer margin 

 of both pairs of wings. The wing expanse is about two and a quarter inches. As the 



•Sanderson, E. D. 'The influence of minimum temneraturrs in limiting the Northern 

 Distribution of Insects.' Jour. Econ. Entom. Vol. I., pp. 245-2C2, 7 maps, 1908. 



