202 INSECTS INJURIOUS TO VEGETATION. 



cut and of Massachusetts, particularly in the valley of the 

 Housatonic, and in the adjoining counties of Dutchess and 

 Columbia in New York. It was first made known to me, in 

 December, 1848, by Dr. Ovid Plumb, of Salisbury, Connecticut, 

 and it is the subject of a communication in the " American 

 Agriculturist," for January, 1849. Since that time. Dr. Plumb 

 has favored me with additional observations, and an account 

 of his experiments with various remedies, and, towards the 

 end of July, 1851, a brief visit to Salisbury gave me an oppor- 

 tunity of seeing the insects in a living condition, and in the 

 midst of their operations upon the trees. This Psylla^ or 

 jumping plant-louse, is one of the kinds whose young are 

 naked, or not covered with a coat of cotton. In some of its 

 forms it is found on pear-trees during most of the time from 

 May to October; and probably two if not more broods are 

 produced in the course of the summer. It was first observed 

 by Dr. Plumb in the spring of 1833, on some imported pear- 

 trees, which had been set the year before. These trees, in the 

 autumn after they were planted, wore an unhealthy aspect, 

 and had patches of a blackish rust upon their branches. Dur- 

 ing the second summer, these trees died; and other trees, upon 

 which the same rusty matter was found, proved to be infested 

 with the same insects. Like the aphides, or plant-lice, these 

 insects live by suction. By means of their suckers, which 

 come from the lower side of the head near the breast, they 

 puncture the bark of the twigs and small branches, and imbibe 

 the sap. They soon gorge themselves to such a degree, that 

 the fluid issues constantly from their bodies in drops, is thrown 

 over the surface of the twigs, and, mingled with their more 

 solid castings, defiles the bark, and gives it the blackish color 

 above noticed. Swarms of flies and ants upon the trees are a 

 sure indication of the presence of these sap-suckers, being 

 attracted by the sweetish fluid thrown out by them. Young 

 trees suffer excessively by the attacks of these insects, nor do 

 old trees escape without injury from them. In consequence 

 apparently of their ravages alone. Dr. Plumb lost several hun- 

 dred pear-trees from 1834 to 1838 inclusive; his trees have 

 continued to suffer, to some extent, from this cause since that 



