112 MASS. EXPERIMENT STATION BULLETIN 160. 



affect the abundance of Phanerotoma considerably, though probably not 

 to the extent indicated by the results of the 1913 investigations. 



In studying the fruit worm parasitism, the writer has had the two 

 following practical objects in view: — 



1. The Possibility of forecasting Seasons of Cheat Fruit Worm Injury. — 

 If relative abundance and scarcity of the parasites in different years has 

 a strong bearing on the comparative abundance of the pest, we should 

 probably be able to foretell with some degree of accuracy, after keeping 

 records of the parasitism for several years, what is to be expected in this 

 regard several months ahead. 



2. The Possibility of increasing the Natural Effectiveness of the Para- 

 sites by harboring them artificially in Some Way. — Not enough has yet 

 been learned about the Chalcidid parasite to make any definite plans in 

 relation to it in this connection. The Braconid {Phanerotoma) , however, 

 can probabl}^ be handled without much difficulty, and experiments are 

 already under way to determine whether its percentage of mortality is 

 much greater under natural out-of-door "dry bog" conditions than it 

 would be if its host worms were kept under the more even conditions of 

 temperature and moisture which they would have in cold storage or in 

 ordinary cellars. It is evident, of course, that on flowed bogs the ma- 

 jority of these Braconid parasites perish during the winter, and if the 

 water is held late (until the latter part of May) they are probably almost 

 exterminated. If, therefore, they can be wintered under artificial condi- 

 tions without much loss, it ought to be possible to replenish the Phanero- 

 toma parasitism on flowed bogs by gathering fruit worms every summer, 

 allowing them to form their cocoons in captivity, wintering them in 

 cold storage and returning the parasites to the bog when they emerge the 

 following season. Of course many unparasitized worms would be win- 

 tered in this process, and as a result many moths would emerge with the 

 parasites, but there is so much difference in size between the moths and 

 parasites that they could be readily separated with a screen. After thej^ 

 were separated the moths, of course, would be destroyed. 



Further submergence tests with fruit worms in their cocoons were 

 begun on September 7, 15 different lots of a dozen each being submerged 

 in water in long glass tubes 2 inches in diameter, at depths varying from 

 4 to 67 inches, on that date. All the worms used in these tests were col- 

 lected from a bog, in their berries, between the 12th and 21st of August. 

 They were submerged seventeen days, being removed from the water 

 on September 24, and were all found to have been killed by the treatment. 

 The tubes were kept in the station screen-house during these tests, and 

 the water may have killed the worms because of its abnormal stagnation 

 and high day temperature. 



On October 19, further submergence tests were started, a part of the 

 cocoons being put in water in tubes in the screen-house as before, while 

 a part were submerged in light netting sacks suspended from a float in 

 a pond. Some of these cocoons were removed from the water on Novem- 



