ENTOMOLOGY. 707 



ENTOMOLOGY. 



The black scale, C. W. Woodworth ( California 8ta. Ept. 1895, pp. 

 ^5o-:J(i:3). — This troublesome pest the author treats at some leugth, 

 giving a description and discussion of its habits aud life liistory, the 

 various causes of death, species of the genus, its economics and its 

 destruction by parasites and diseases, as Avell as the fungus, black 

 smut, that follows its attack. 



In discussing the economics of the scale he divides the injuries done 

 by it into 3 classes, /. c, those caused by (1) the removal of sap, (2) 

 injuring the plant through puncturing, and (3) the excretions of the 

 insects, Avhich with tlie dust that accumulates serve as a nidus for 

 the growth of fungi. 



The injury through the removal of sap occurs when the plant, in the 

 hot climate of California, can least aftbrd to lose even the smallest 

 amount of moisture. Little injury is done by puncturing when the 

 insects are few, but when they are so numerous as to surround the 

 branch they iiractically affect the whole of the living tissue, throwing 

 it into a passive or resting state. As a consequence the branch 

 assumes the appearance commonly known as "hidebound," giving the 

 tree a dried-up ai>pearance. The injuries by the excretions are not all 

 direct. The collections of excrement, dust, and fungi injure by hinder- 

 ing the action of the sun upon the chlorophyll of the leaf, thus inter- 

 fering with the food supply of the plant; and furthermore by 

 disfiguring the fruit, they reduce its nuirket value and cause an 

 expense for washing. Such injuries are serious in the case of citrus 

 fruits and are very much in excess of the cost of the most expensive 

 of remedies, namely, the gas treatment. 



The cause of the death the author attributes largely to the attacks 

 of disease. Parasites form a prominent factor in the destruction of 

 the scale, but not so prominent a one as has been supposed. 



"They take some part in the destruction of the l>laek scale. Tlio common native 

 Chalcid is estimated by I'rofessor Howard to destroy 75 per cent, but this only 

 means that 3 out of 4 of those that canu^ to adult size contained the ])arasite; that 

 is, less than 1 per cent of those hatched. I have never known of a case where more' 

 than 2 per cent were destroyed from tliis cause. The other 9X per cent met some 

 other fate. . . . 



"The black scale is very snl)ject to disease. The diseases seem to be similar to, if 

 not identical with, those ■wlii<h destroy the chiucli bug iii the Mississippi Valley. 

 On a tree well infested with black scale, I have seldom met with a death rate of less 

 than 90 per cent, evidently from this cause, occurring between the time the eggs are 

 laid to the time of the second moult. 



"There is a consideivible number that crawl down the trunk, or drop from tlie 

 tree, and occasicmally there is a wholesale destruction due to a hot, dry wiiul, or 

 some such meteorological condition. 



"The number ordinarily destroyed by ladybirds is much smaller than is usually 

 supposed. Ladybirds aud tlieir larva- are to be met with more abundantly in other 

 situations tiian in scale-infested trees; indeed it is the exception to find them par- 

 ticularly abundant on such trees. On the University grounds in Berkelej', the only 



