SCALE INSECTS ON DECIDUOUS AND ORNAMENTAL TREES. 



By S F. CHAPIN, M. D., 



\', -/Y< xitli'n.t uj til ai<'.. Hoard of Horticultural Commissioner 8. 



A Report to the State Board of Horticultural Commissioners. 



^Reprinted for the Aiithor from the PACIFIC RURAL PRESS of Oct. 28 and Nov. 4, 1882.] 



The prevalence of scale insects in the or- 

 chards of Santa Clara valley during the past 

 few years has afforded ample scope for their 

 study, to which I have, for the past three sea- 

 sons, devoted what time I could command. 

 Assigned to this work by you, I shall report as 

 concisely as possible the information gained and 

 the results obtained by numerous experiments 

 carried on and observed for two seasons. I 

 shall here use in this paper as a part of it, a re- 

 port presented to the Santa Clara County Hor- 

 ticultural Society, August 6, 1881, by Mr. D. 

 C. Vestal and myself, with such revision and 

 correction as another year has shown to be 

 needed, and with added memoranda to the ex- 

 periments detailed, in order to present their 

 full effects after a lapse of more than a year. I 

 shall also detail other experiments,and shall re- 

 fer to work done on an extensive scale for the 

 destruction of the scale pests, and which has 

 shown most gratifying result.-. 



All scale insects impair, to a greater or less 

 degree, the vitality and productiveness of the 

 tree or plant upon which they live. Of the 

 seven species which have here been observed as 

 infecting our deciduous orchard trees and fruits, 

 five are of frequency and of such importance as 

 to attract the attention of orchardists. These 

 are the Lecanium Olecz, Aspidiotus Rapax, 

 Aspidiotus Conchiformis, Aspidiotus Pernic- 

 iousus and the Icerya Purchasi, the two last 

 named being the most dangerous of all scale 

 pests which the orchardist has to encounter. 



Lecanium Oltte. This scale is beginning to 

 attack other trees than the orange and its kin- 

 dred. A year since I examined an orchard 

 where it existed in overwhelming numbers 

 upon the German prune, Brigg's Hed May and 

 the Early Crawford peaches, upon the Moor- 

 park apricot trees, and most of all upon the 

 Petite prune d'agen trees. This is believed to be 

 the direct result of planting a few orange trees 

 close by. Mr. Ellwood Cooper has written 

 fully upon this scale, and to whose reports I 

 refer you. 



Aspidiotus Rapax. So named by Prof. J. H. 

 Com stock. This scale is rapidly spreading, and 

 is now found in many places where unknown 

 a year or two ago. It seems to be most 



337 



nent in Santa Cruz county, where it can be 

 abundantly found. I have, during the past two 

 seasons, observed it in many places in Santa 

 Clara county, and have had specimens sent me 

 from San Lorenzo, Alameda county, where it 

 was abundant upon pear trees, a branch sent 

 being well covered with the old scale, and also 

 newly hatched young crawling about. 



This scale seems to be native to the willow 

 and alder and other indigenous trees. It, how* 

 ever, is found in great numbers upon acacia 

 trees, upon the black locust and poplar, and 

 upon some of our orchard trees, as the pear and 

 apple. This scale somewhat resembles the 

 Aspidiotus perniciosus, and by many is con- 

 founded with it, but it is not to be compared to 

 the latter for destructiveness. 



Aspidiotus Conchiformis. The one longest 

 known, and which was discovered and described 

 in Maine in 1794, has ever since that time in- 

 fested the apple tree particularly, although 

 found upon other fruit trees and upon the cur- 

 rant. This is now found in great numbers upon 

 almost all old apple trees on this coast, and is 

 commonly known as the bark louse or the 

 oyster- shell scale. It may be found described 

 in works on entomology. This species has not 

 caused so much injury as to alarm fruit grow- 

 ers to any great extent, although it is described 

 by Dr. Packard as doing more injury to the 

 apple tree than any other insect known. 



Cottony Cushion Scale. 



Next will be described a comparatively new 

 scale heretofore, but one which has within the 

 last two or three years been ravaging many lo- 

 calities in widely different parts of the State. 

 This is the so-called dorthesia, or, as named by 

 Maskell, Icerya Purclmsi, and called by Mr. 

 Matthew Cooke the cottony cushion scale. 



This scale has been, it is asserted, known to 

 be on the acacia for seven years in San Jose, but 

 it is only during the past and present seasons 

 that it has attracted attention. Its great pro- 

 litiouess and its destructive abilities have called 

 widespread attention to it. This pest attacks 

 everything in the way of tree, vine or shrub; 

 all the evergreens as well as deciduous trees 

 llhatifatt in its way are attacked, and every orna- 



