■' 1919 ENTOMOLOGICAL SOCIETY. 65 



mottled and malformed and the plants finally die. The disease is a very important 

 one and is said to be spreading. It was formerly thought to be due to malnutrition, 

 but is now known to be a communicable disease, the virus of which is transmitted 

 chiefly by the aphis (Macrosiphum solanifolii) but also to a lesser extent by another 

 aphis (Rhopalosiphum persicae) and by the Tarnished Plant Bug (Lygtis pratensis). 

 The most interesting discovery in connection with this disease is that not only 

 do aphids transmit it but also that their offspring down to the fourth generation 

 can do so even though none of these offspring have fed upon diseased plants. 



McClintock and Smith who made the above discovery think it very probable 

 that aphids are also responsible for the tiding over in their own body of the disease 

 from spring to fall. 



In conclusion we may point out that the plan of controlling such diseases 

 as are spread chiefly by insects by destroying the insects responsible, is in most 

 cases impracticable; because some of the worst offenders, such as the Striped 

 Cucumber Beetle, several species of aphids and the Tarnished Plant Bug, are 

 among the most difficult of insects to combat successfully. 



It is also worth while pointing out that it is only during the last few years 

 'that any careful study has been made of insects as agents in the dissemination 

 of plant diseases, and that though some very brilliant work has been done, especially 

 during the last four or five years, there still remains great scope for further careful 

 investigation by entomologists and plant pathologists working together in close 

 co-operation. 



The More Important Literature Consulted. 



Eastham. The part played by insects in the spread of plant diseases. Proc. 

 Ent. Soc. of B.C. 



Massee. Textbook of fungi. 



Sturgis. Some aspects of vegetable pathology and the conditions which 

 influence the dissemination of plant diseases. Bot. Gaz., Vol. XXV, p. 187,' 1898. 



Hopkins. Preliminary report on insect enemies of forests in the Northwest. 

 Bui. 21 (n.s.), Bur. Ent., U.S.D.A. 



Primm. The European Canker in the vicinity of Philadelphia, Pennsylvania. 

 Jour. Econ. Ent., Vol XI, No. 1, 1918. 



Martin. Dissemination of Septoria lycopersici by insects and pickers. 

 Phytopathology, Vol. VIII, No. 7, 1918. 



Studhaltfr. Insects as carriers of the Chestnut Blight. Phytopathology, 

 Vol. IV, No. 1, 1914. 



Studhalter and Ruggles. Insects as carriers of Chestnut Blight. Bui. 12, 

 Penn. Dept. of Forestry. 1915. 



Anderson and Eankin. Endothia Canker of chestnut. Bui. 347, Cornell 

 University. 1914. 



Gravatt and Posey. Gipsy Moth larvae as agents in the dissemination of 

 the White Pine Blister Eust. Jour. Agr. Research, Vol. XII, No. 7, 1918. 



Gravatt and Marshall. Arthropods and gasteropods as carriers of 

 Cronartium ribicola. Phytopathology, Vol. VII, No. 5, 1917. 



Parrott and Fulton. Tree-crickets injurious to orchard and garden fruits. 

 Bui. 388, N.Y. Agr. Exp. Sta., Geneva. 1914. 



5-E. 



