"Rfax York Agricultural Experiment IStatio.x. 383 



These insects have, in their normal habitat, a large number of 

 natural enemies, the most important of which belong to the orders 

 Hymenoptera and Diptera. In spite of the large numbers of the 

 moths' eggs imported into the United States, the lepidopterons 

 were apparently unaccompanied by their more common and efficient 

 parasites. An ichneumon, Mesochorus sp., was obtained from 

 padellus reared on cherry, and a tachinid, Exorista arvicola Meigen, 

 was quite abundant in some colonies of malinellus caterpillars 

 subsisting on apple. 



Comparisons of the structures of the caterpillars and of the male 

 genitalia show no tangible structural differences between padellus 

 and malinellus. The absence of differential features suggests that 

 the moths from 'hawthorn and cherry and those from apple consti- 

 tute a single species; but cross breeding experiments are desirable 

 to settle definitely the status of the two forms. 



An outbreak of these insects is to be expected from two sources: 

 (i) From the annual importation of infested foreign-grown nursery 

 stock, and (2) from spread of the pests that may have established 

 themselves along the avenues of trade in previous shipments. The 

 remedy is careful inspection of nurseries during June and the 

 destruction of infested plants. As fruit pests, the insects would 

 prove amenable to prevailing spraying practices. 



INTRODUCTION. 



A study of the insect outbreaks from year to year in the State of 

 New York will impress one with the number of introduced species 

 and their great importance to its fruit interests. These constitute 

 a steady and a severe drain on its horticultural resources. Many of 

 the principal introductions in the past had their origin in Europe, 

 and in the diverse and constantly increasing intercourse with the 

 United States there is a marked trend of migration of the common 

 and destructive species to this country. Common pests of fruit 

 trees in all parts of the continent are certain insects, known as 

 " ermine moths," which are discussed in almost every leading work 

 upon European economic entomology. Interest is now directed to 

 these insects as they have during recent years been brought into this 

 State in considerable numbers in foreign importations of nursery 

 stock. It is desired to call attention to their injurious nature, the 

 circumstances of their discovery and the danger that exists of these 

 pests being introduced, if they have not already become established. 



THE ERMINE MOTHS. 



GENERAL CHARACTERS. 



These moths constitute the genus Yponomeuta of the family 

 Yponomeutidoe. In Dyar's list of North American Lepidoptera this 



