New York Agricultural Experiment Station. 405 



for purposes of exportation are indicated by Dr. L. O. Howard in 

 the following communication: ^ 



"I saw them (Yponomeuta spp.) everywhere on my recent trip 

 in France, and especially upon the hedges and trees at the borders 

 of the plats of seedlings being grown for exportation to America. 

 I saw Yponomeuta larvse in their webs on almost every apple tree, 

 sometimes only here and there a twig with some leaves webbed 

 together, and occasionally considerable numbers of these webs." 

 During years favorable for the multiplication of these insects, the 

 chance of nursery stock becoming infested when grown under 

 such circumstances is obviously very great, as has been well 

 demonstrated. 



FEEDING HABITS OF THE CATERPILLAR. 



Before transplanting in the nurseries the seedlings are stubbed, 

 making a plant which, including the root, measures from fifteen to 

 eighteen inches in length, while the stalk has a diameter of about 

 one-quarter of an inch and bears from five to ten leaf buds. The 

 egg masses of the insects are generally found on the stalk within 

 six to nine inches of the ground, and from one to three egg masses 

 have been detected on a plant. These were placed just under or 

 above a leaf bud, almost touching it, or in positions intermediate 

 between two buds. Opportunity has not been afforded to observe 

 the early movements of the larvtB but, judging from the conditions 

 of leaf clusters, it would appear that the young caterpillars on 

 emerging from the egg mass preferred the nearest opened bud above 

 them, while dormant buds were passed by unharmed. Our obser- 

 vations indicated that the caterpillars on apple seedlings were, at 

 this stage, leaf miners. The first leaves attacked by them showed 

 along the margins near the tips reddish or rusty-colored blotches of 

 varying sizes, and as a result of this injury the leaves were small as 

 if stunted, while others were one-half destroyed or entirely killed. 

 On abandoning their " mines " the caterpillars ascended higher on 

 the seedlings and, on June 12, when first detected, were feeding 

 openly on some of the upper leaf clusters on the central stalk of the 

 plants or at the base of the terminal offshoots which were then from 

 three to four inches in length. They spun a filmy tangle of fine 

 silken threads between two leaves and proceeded to consume the 

 upper pulpy tissues of the under leaf, while the lower epidermis was 

 seldom or little eaten and served as the floor of their feeding grounds. 

 The rejected portion of the leaf was at this time of a thin papery 

 nature, light brown or reddish-brown in color, showing plainly the 

 network of little veinlets, and is characteristic of the work of the 

 insects at this stage. The caterpillars are social insects, feeding 



1 Letter of Aug. 18, 1909. 



