INSECTS AS CARRIERS OF THE CHESTNUT 

 BLIGHT FUNGUS! 



HISTORICAL INTRODUCTION. 



The relation which various insects bear to the dissemination 

 of plant diseases is a subject which has received the attention 

 of a large number of plant pathologists within recent years. 

 In the majority of cases, however, in which insects have been 

 held responsible for the spread of plant diseases, the evidence 

 given in support of the accusation was quite meager and only 

 circumstantial. In presenting a review of the literature bear- 

 ing on this subject, no claim is made for completeness; it is 

 our intention merely to point out some of the noteworthy 

 instances in which insects have been considered responsible for 

 the dissemination of fungi or bacteria which are saprophytic 

 or paratitic upon plants. 



Taking up first the bacterial side of the question, we find 

 that as early as 1802 Waite (53, 54) reported definite experi- 

 ments to show that the fire blight of the pear and the apple 

 can be carried by insects. Bees, wasps, and flies were shown 

 to carry the causal bacteria from blossom to blossom, and 

 Waite showed that this mode of dissemination was the cause 

 of the rapid spread of the disease in the spring. Furthermore, 

 this author believed that the twig blight, caused by the same 

 organism, frequently had its origin from bacteria carried by 

 insects, although no experimental data are cited on this point. 

 That this supposition is correct has since been proved by a 

 number of workers. Extensive observations made by Jones 

 (28) strongly indicated that new infections of the twigs of 

 apples after the blossoming season were due largely to trans- 

 mission by aphids, and this same author has also shown (28, 

 29) that the bark boring beetle, Scolytus rugulosus, causes 



^Investigations conducted jointly by the Office of Forest Pathology, Bureau of Plant 

 Industry, and the Pennsylvania Chestnut Tree Blight Commission. 



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