160 ORDER HOMOPTERA. 



live seasons from this insect : the young leaves of the first product curled, thickened, 

 became red or brown, and most of them perished. The trees aftenvards put forth a new 

 crop of leaves, and all survived, though the fruit was destroyed in the blossom. ( For a 

 delineation of the peachtree aphis, see Plate xxix, fig. 7.) 



It is evident from the foregoing remarks, that plant-lice are injurious, both tlirough the 

 wounds they inflict uix)n the parts of the plant they inhabit, and from the fluids or nu- 

 triment they abstract from the circulation. As a family, their habits are the same, but 

 some species or kinds appear to be more injurious than others ; and it seems difficult to 

 account for all the effects they produce, unless they possess a poisonous principle. In 

 support of this observation, I may state that the pear is infested with a kind that kills the 

 tree when young. Of this fact, I was informed by Dr. Ovid Plumb of Salisbury (Connecti- 

 cut) : the limbs or twigs which he showed me were brown and dry in patches. Afterwards 

 Mr. Haebis of Cambridge investigated the matter, the results of wliich he has commimi- 

 cated in his work on insects injurious to vegetation. Dr. Plumb, who was the first to notice 

 these minute parasites of the pear-tree, entered with much zeal and spirit into the in- 

 vestigation of their eifects, and of the remedies to destroy them. 



The genus to which this insect belongs is Psylla, one of the jumping plant-lice, but 

 destitute of the cotton-like covering. From the observations of Dr. Plumb, it appears to 

 give birth to two or more broods during the year, being found upon the pear from May 

 to October. They first appeared upon imported trees. My own trees, which were obtained 

 fix>m Rochester, and were also imported, had many limbs that appeared rusty and dry ; 

 and though these limbs were lost, the trees survived. The appearances of the limbs were 

 similar to those of the branches preserved by Dr. Plumb ; but I was unable to find the 

 aphis, although I sought for it diligently. 



This insect is described as of a dull orange color, and one-tenth of an inch long when 

 perfect : the thorax is brownish orange. The female is more pointed behind than the male. 

 According to Mr. Harris, it may prove to be the Psylla pyn of Europe. It may be well 

 to remark, that when the branches of a pear-tree become dark and dry in patches, it is 

 advisable to search for this insect. The remedies recommended are, first, rubbing off the 

 lice with a brush. Mr. Harris advises the application of strong soapsuds with sulphur, 

 by means of a brush, before the buds expand : so also the use of whale-oil soap*. 



The insects of the Genus Thrips, likewise belonging to the Family ApHiniDiE, are also 

 injurious. Their wings, instead of lying obliquely upon their backs as in the Genus Aphis, 

 lie flat, and are fringed. They are supposed to poison plants by their puncture, producing 

 thereby curls and a thickening of the tissues of the leaf. They may be treated with soap 

 and water, or whale-oil soap dissolved in water : a strong decoction of tansy may serve. 



* Harris on Insects injurious to vegetation, p. 202. 



