No. 8. 



Disease of the Plum Tree. 



257 



For the Farmers' Cabinet. 

 Disease of the Plum Tree. 



Messrs. Editors, — My attention was 

 called a few days ago, to an article in the 

 New Genesee Farmer, on the " Black Can- 

 ker," as it is called, in the plum tree. As 

 there seems to be some difference of opin- 

 ion in regard to the origin of the disease, I 

 embrace this opportunity, through the me- 

 dium of your valuable periodical, to make 

 known the result of a few observations, on 

 what I conceive to be the origin of this dis- 

 ease. 



From the examinations which I have made 

 of the trees in this vicinity, I have arrived 

 at the conclusion that the disease in ques- 

 tion, is produced by the deposit of the eggs, 

 and the subsequent evolution of the larva of 

 an insect, which I believe to be identical 

 with, or allied to, the cegeria exitiosa, well 

 known as the insidious destroyer of the 

 peach tree. 



Previous to my having detected this in- 

 sect upon the plum tree, I occasionally met 

 with it in my garden, in the act of collect- 

 ing honey : when thus employed, it is rapid 

 in its motions and difficult to capture. 

 Amongst those taken upon the wing, or 

 reared from the pupa, I have not detected a 

 single female, and on examination, I find 

 they agree in many particulars, with the 

 figure and description of the male of the 

 peach tree insect — "ageria exitiosa" — as 

 given by Mr. Say, in his North American 

 Entomology. 



Many of the perfect insects varied in 

 size ; but this variation, I suppose to depend 

 in a great measure upon the quantity of 

 food afforded them while in the larva state. 

 In some instances I have observed them to 

 be larger or smaller, according to the size 

 of the branch which they occupied. 



One half of the follicle* which encloses 

 the pupa of this insect, is formed by a slight 

 excavation in the wood of the tree, sufficient 

 to receive the lateral half of the body, the 

 remainder is composed of small pieces of 

 bark, connected together by the web of the 

 insect, and resembles, in appearance, the 

 follicles found at the root of the peach tree 



The pupas have two semifascia of spines, 

 upon each segment of the abdomen, except 

 the three last, which have but a single row 

 only, agreeing in this respect, with the pupa 

 of the peach tree insect, above mentioned 

 The object of these spines appears to be, to 

 assist in propelling the body forward, and to 

 effect this, the insect has recourse to a ro- 

 tary motion. In one instance, I made a 



* Follicle, a cocoon. 



small opening in the end of a follicle, next 

 to the head, and in a short time the pupa 

 escaped from it, while in an upright posi- 

 tion, and in the manner before mentioned. 



This accounts for the exuvia\ being often 

 found at some distance from the follicle, 

 generally extruded half way through an 

 orifice in the outer bark, in which position 

 it is left by the insect, where it may fre- 

 quently be seen at this season of the year. 



On the 20th of last August, I examined 

 a tree of the blue damson plum in my gar- 

 den, which was very much diseased ; larva? 

 nearly full grown, together with pupae in 

 different stages of maturity, were found in 

 the same diseased branch ; not more than 

 three or four empty follicles were found, 

 showing, that up to this period, but few per- 

 fect insects had escaped. 



The pupse and follicles which I obtained, 

 were placed under a bell glass in my house, 

 and I find by referring to my Entomological 

 journal, that by the 2nd of September, they 

 had all, with the exception of one, under- 

 gone their final metamorphosis : upon open- 

 ing this follicle, I found the pupa had been 

 entirely destroyed by a number of small 

 larva?, which occupied the interior; these in 

 a few days changed into pupe, without en- 

 closing themselves in separate cocoons, as I 

 have observed in one instance, of a parasite 

 of the peach tree insect. 



About the beginning of September, I re- 

 newed my examinations of the trees; no 

 pupa were now to be found, the empty folli- 

 cles indicating that they had all taken their 

 flight. Here and there, I detected a larva, 

 which was very feeble and appeared to be 

 diseased ; but they, notwithstanding, exhib- 

 ited considerable tenacity, as they lived se- 

 veral days without food, under a bell glass. 

 From the 1st of September until the begin- 

 ning of October, I did not succeed in detect- 

 ing any pupa? in the trees, but occasionally I 

 met with a larva which appeared to be in 

 the condition above mentioned. My atten- 

 tion being very much absorbed by profes- 

 sional duties about this period, I neglected 

 to observe their farther progress, but I in- 

 tend, during the next summer, to continue 

 my researches, with a view to discover more 

 of their habits and economy. 



W. D. H. 



West Chester, Pa., Feb. 1st, 1843. 



We trust our friend will be good enough to furnish 

 us with the result of his researches, in relation to this 

 subject. Should they lead him, or be the means of di- 

 recting the attention of others, to the true cause of a 

 disease which is widely deplored, he will merit the 

 thanks of every lover of fine fruit. Ed. 



t Exuvia, the shell thrown off by the insect, when it 

 assumes the winged state. 



