New York AoRicuLTrn.VL Experiment Station. 



4on 



is a striking illustration of how foreign insects upon their introduction 

 into the United States may find their struggle for existence a com- 

 paratively easy one, and by virtue of the balance in their favor 

 become a serious item for economic consideration. 



From padellus taken from cherry seedlings in New York we have 

 bred a few specimens of Mesochoriis sp., while the most common 

 parasite of both padellus and malinellus was the tachinid, Exorista 

 arvicola Meig. Some colonies had as many as 25 per ct. of the 

 caterpillars carrying from one to three eggs of this fly, which were 

 in the constrictions principally of the head and thoracic segments. 

 The eggs are of a cream color and measure about .52 mm. long, 



9 



10 



An Ermine Moth Parasite, Exorista arvicola Meigen. 

 8, Eggs on malinellus caterpillar; 9, puparium in malinellus pupa; 10, adult. 



(All figures enlarged, last greatly) 



.33 mm. wide and .19 mm. high. They are oval in shape, one end 

 being broader than the other and are convex on the upper side. 

 The surface is smooth and is covered with a delicate tracing of raised 

 lines which give the appearance of a network of cells, pentagonal or 

 hexagonal in outline. In hatching, a crack forms around the base 

 about the wider end and extends upwards around the sides to about 

 the middle. The portion above the crack raises up like a lid. The 

 eggs of arvicola were first observed on mature caterpillars on June 

 25, 1912, which began to pupate on July 2. Moths from non- 

 parasitized caterpillars commenced to emerge on July 10, while the 

 tachinids appeared from July 10 to July 12. 



A capsid,^ Atraciotomus mali Meig., is listed as an enemy of the 

 ermine moths, and starlings ^ are said to feed upon the caterpillars. 



1 Pommerol, Rev. sc. Bourbonn. 14:18-23, 1901. 



2 Theobald, 2nd Kept. p. 35, 1904. 



