DEVELOPMENT OF THE PAEASITES. 59 



possible, for further experimentation or for determination. It is 

 inadvisable to isolate many of the parasites until the larva is partially- 

 developed, as the isolation seems to dry out both food and larva. 

 In the study of the parasites all those in the same stage were placed 

 on the same tray. When they passed to the next stage in develop- 

 ment they were transferred to another tray. In this manner an accu- 

 rate record was kept of the development. In order to determine the 

 total length of the breeding period it seems best to take the total 

 period from the collection of the material to the maturity of the last 

 specimen and add a plus mark ( + ) to this figure. The total period 

 can hardly be more than 2 or 3 days longer than the longest period 

 thus obtained, as the egg period is very seldom more than 3 days. 

 To obtain the exact length of the pupal period, the maximum period 

 is taken to be the longest time from the observation of a fresh or 

 newly-formed pupa to maturity, and the minimum time is taken to be 

 the shortest period from the observation of the grown larva to ma- 

 turity. Having thus accurately defined the pupal stage, the relative 

 limits of the egg and larval stages are obtained by subtracting 

 the pupal stage from the total developmental period. Table XX, 

 which follows, presents all of the available data as they have been 

 reduced in this manner to show the length of development of the 

 various stages. It will be seen that most of the species pass their 

 entire developmental period in from 20 to 30 days between June and 

 October 15, but that after the middle of October the developing 

 stages are caught by the cold weather and the development is sus- 

 pended until spring. Thus, it is noticeable that parasites becoming 

 larvae in earty October and November have a short larval period of 

 probably less than 20 days, becoming pupse before the cold wave 

 and passing a pupal period of about 150 days. Parasite larvsB 

 which hatch a little later are caught in the larval stage and hibernate 

 thus for from 120 to 150 days, then becoming pupae and maturing 

 in from 15 to 40 days. It will be noticed that Microhracon mellitor, 

 Eurytoma tylodermatis , and the two species of Catolaccus have short 

 developmental periods during the summer, while the species of 

 Cerambycobius have a little longer period. It will be noticed that 

 Eahrocytus piercei has only appeared in the fall of the year. This 

 species has been recorded four years in succession and never before 

 October. On the other hand, Microdontomerus anthonomi seems to 

 be almost exclusively a summer parasite, having never been recorded 

 after September. Of course the species of which we have records 

 throughout the breeding season are the ones most important. This 

 statement is borne out by the figures on the relative numbers and 

 importance of the different species. 



