390 THE MONTHLY BULLETIN. 



grove during his recent investigations in Florida the writer was obliged to disinfect or 

 "dip" as many as eight times in one day. 



Early in the campaign to eradicate citrus canker from the groves of Florida it 

 was found that these three factors were not sufficient and it hv.ime necessary by- 

 means of quarantine to control the movement of articles likely to carry infection 

 and which from their very nature were not readily susceptible to disinfection. It 

 was found also that citrus canker bacteria might be present but remain dormant for 

 many months. No amount of inspection could detect an infection of this kind. This 

 danger was especially acute in the case of citrus nurseries where a dormant infection 

 might not be discovered until the nursery stock had been moved, planted out in 

 groves and then a new center of infection developed. To meet this situation the 

 State Plant Board adopted a rule establishing quarantine zones about infected prop- 

 erties. These zones contain all that territory within a mile in any direction from 

 the outside boundaries of a grove in which infection is found. The movement of 

 citrus nursery stock from nurseries situated within such a mile zone is prohibited t<> 

 points outside such zones. On the preservation of this quarantined area aboul 

 infected groves, on the strict enforcement of the necessary sanitary precautions, on 

 the continued and careful inspection to find and destroy as quickly as possible the 

 infected trees depends the success of the campaign to eradicate citrus canker. 



THE PEAR WOOLLY APHIS. 



By W. M. Davidson.-]' United States Bureau of Entomology, Deciduous Fruit Insect 

 Investigations, Sacramento, C'al. 



Introduction. 



Owing lo great similarity in general appearance the woolly aphis of the pear 

 (EtioBoma pyricola, Baker & Davidson)* (1) has until recently been coufused with 

 the woolly aphis of the apple (Enosoma lonigera, Hausmann). To the naked eye 

 the two insects are hardly distinguishable, but the assistance of a magnifying lens 

 shows that the wax threads on the pear species are stiffer and stouter than those 

 on the apple insect, while the body color of the former is, except in newly-molted 

 individuals, considerably paler than that of the latter. The pear species is also 

 much more elongate in form. 



Unlike the woolly aphis of the apple which occurs both above and below ground 

 the pear woolly aphis infests only the subterranean portion of the pear tree, the 

 woolly aphis sometimes encountered on limbs of certain varieties of pears, 

 e. g., Winter Nelis and Easter Beurre, being Eriosoma lanigera. 



The project embracing the investigation of the pear woolly aphis was undertaken 

 at the instance of Dr. A. L. Quaintance, Bureau of Entomology, in charge of 

 deciduous fruit insect investigations. The studies were made principally at Walnut 

 Creek, California, during the years 1915 and 1910. The writer wishes to express 

 bis thanks to Mr. R. L. Nougaret, Bureau of Entomology, for helpful suggestions, 

 to Mr. V. G. Stevens for his services in field and laboratory while employed in the 

 Bureau of Entomology, to Mr. George P. Weldou, California State Commission of 

 Horticulture, to Mr. F. C. Reimer, superintendent Southern Oregon State Experi- 

 ment Station, and to the county horticultural commissioners within whose territories 

 the woolly aphis exists, for helpful cooperation. 



Distribution. 



The insect has without doubt existed in California for over twenty years and is 

 now established throughout the pear-growing sections of northern and central Cali- 

 fornia. According to reports received from county horticultural commissioners, it 

 does not occur south of Tehachapi Pass nor in the region of the southern end 

 of the San Joaquin Valley. In these districts the acreage in pears is relatively 

 small. In the Santa Clara and San Ramon valleys, throughout the foothill regions 

 of the Sacramento Valley and in the "delta" section the aphis is abundant. In 

 southern Oregon the insect is widespread and the damage is similar to that caused 

 in California. The insect has been taken in Ohio on pears the year after they were 

 imported from Europe, while galls on the alternate host, the elm, have occurred in 



tPubllshed by the permission of the Secretary of Agriculture. 



•Figures In parentheses refer to "Literature Cited" at the conclusion of the article. 



