CORNELL UxNIVERSITY EXPERIMENT STATION BULLETINS. 255 



distinguishing it from that species; and nearly all of our entomologists 

 have written of it under this name. Psylla pyricola sometimes attacks the 

 apple tree in Europe, but it seems to confine its attacks to the pear in 

 this country. 



INDICATIONS OF ITS PRESENCE. 



Among the first indications that pear-growers, who suffered from this 

 pest in 1891, had of its presence was the noticeably lessened vitality of 

 their trees early in the season. Old trees, especially, put forth but little 

 new growth. Where new growth started, in many cases, the shoots began 

 to droop and wither in May as if from a loss of sap. A little later, whole 

 trees put on a sickly appearance; the leaves turned yellow and the fruit 

 grew but little. By midsummer nearly all the leaves and half-formed fruit 

 fell from many trees; this fact suggested the design on the title page of 

 this bulletin. 



Another peculiar phase of the attack was the immense quantities of a 

 sweet water-like fluid called honey-dew which covered the twigs, branches, 

 and trunks of the trees. In some instances it appeared in such quantities 

 that it literally rained from the trees upon the vegetation beneath; in cul- 

 tivating the orchard the back of the horse and the harness often became 

 covered with the sticky substance dropping from the trees; in gathering 

 what little fruit matured the hands and clothing would become smeared 

 with the sticky fluid. This honey-dew appears on the trees soon after 

 the leaves expand and is found throughout the season. It attracts 

 thousands of ants, bees, and wasps which feed upon it. If copious showers 

 fall during the early part of the season much of this honey-dew is washed 

 off, making it less noticeable. 



At first the honey-dew is clear like water, but soon a black substance 

 appears and, spreading rapidly all through it, gives it a disgusting blackish 

 appearance as if the trees were covered with smoke from a factory. This 

 black growth is a fungus, Fumago salicina, which grows luxuriantly within 

 the honey-dew, but does not attack the tree. It forms, however, with 

 the honey-dew, a coating which must close many of the breathing pores 

 of the tree and thus materially affect its healthy growth. Many trees 

 appeared as though treated with a thin coat of black paint. 



The attention of the entomological department of this station was first 

 called to the pest by Mr. H. S. Weight, Ithaca, N. Y., in the latter part 

 of November, 1891; or not until the insect had done its damage for the 

 season. A visit to his orchard a few days later revealed a most deplorable 

 state of affairs. The whole orchard appeared as though a fire had swept; 

 quickly through it and scorched the trees, blackening the trunks, large 

 branches, and the smallest twigs; both young and old trees of dwarf and 

 standard varieties had been attacked, the Bartlett and Duchess varieties 

 suffering the most; most of the trees had made little or no new growth dur- 

 the season, and many buds were then dead. Neighboring orchards were 

 similarly affected; and Mr. G. T. Powell reported that his orchards at 

 Grhent, N. Y., presented a similar appearance. Several trees in some 

 orchards died before spring. 



Although the indications of the presence of some enemy is thus so 

 conspicuous, the depredator is an insect so small as to be easily overlooked. 



