62 PROTECTION OF PLANTS, 1918-19 



aphis (A. pomi). Later^*', he proved that the tarnished plant bug, {{Lygus pra- 

 tensis) was the most effective disseminator of the disease in New York State. In 

 1915, Stewart and Leonard^^ added four bugs to the list of proved fireblight 

 carriers. These were Adelphocoris rapidus Say, Campylomma verbasci Herrick- 

 Schaeffer, Orthotyliis flavosparsus Sahlberg and Poeciloscystus basalts Reuter. 

 Several other sucking insects have been proved to spread the disease, and it is 

 quite definitely known that any sucking insect feeding on infected trees is a 

 potential carrier. The fireblight bacillus occurs in large numbers in a sticky 

 exudate and readily adheres to any insect which may feed on the plant. Since 

 the bacillus, except in the case of blossom blight, can enter the host tissues only 

 through a wound, it is evident that those insects which puncture the plant are 

 tlie most effective in spreading the disease. 



The European Apple tree canker (Necfria ditissima) is often spread by means 

 of aphids (Descours Desacres). 



Boring insects may also introduce the germs of disease directly into 

 the tissues of healthy plants. Jones^ collected specimens of the fruit bark beetle 

 {Eccoptogaster rugulosus) from a blighted pear tree and allowed them to run over 

 prepared agar and gelatin plates. Copious bacterial growth followed the tracks of 

 the beetles, and of this growth thirty to seventy-five per cent was of the fire- 

 blight organism {B. amylovorus) . He also observed that blight often developed in 

 the immediate neighbourhood of the burrows of this insect, and concludes that 

 the fruit-bark beetle is one means of spreading blight in both apple and pear trees. 



Studhalter^- found that the longicorn borer, Leptostylus macula feeds on the 

 pustules of the chestnut blight fungus (Endothia parasitica) and may carry as 

 many as 337,000 spores of this fungus on its body. As this insect often breeds in 

 the chestnut it must be a fertile means of distributing infection. In addition to 

 L. macula, Studhalter found spores of Endothia on the bodies of eighteen species 

 of insects. 



Leaf-eating insects may convey disease organisms on their mouthparts 

 or bodies to healthy plants and introduce them into the tissues through the 

 wounds which they make in feeding. 



Erwin Smith^^ was able to readily spread the bacterial wilt of cucurbits (B. 

 tracheiphilus) by means of the striped cucumber beetle {Diabrotica vittata), and 

 he considers this insect the chief means of natural dissemination. He says 



^^ Stewart, V. B. The importance of the tarnished plant bug in the dissemination of fireblight 

 in nursery stock. Phytopathology III, pp. 273-276. 1913. 



" Stewart, V. B. and Leonard, M. D. The role of sucking insects in the dissemination of fire- 

 blight bacteria. Phytopathology V, pp. 115-123. 1915. 



^^ Studhalter, R. A. Insects as carriers of the chestnut blight fungus (Abstract). Phytopatho- 

 logy IV, pp. 52, 1914. 



" Smith, Erwin F. Bacteria in relation to plant disease. Vol.11. Carn. Inst. Wash. 1911. 



