64 PROTECTIOX OF PLAXTS, 1918-19 



The spores of the brown rot fungus often enter through curculio punctures. 

 The trichosphaeria disease of sugar-cane enters through the tunnels of the 

 various cane borers. 



Do Insects Carry Disease Germs over Winter? 



The possibihty of hibernating insects carrying disease germs over winter has 

 attracted considerable attention, but the only definite work known to the waiter 

 in which the results were partially positive is that of Rand and Enlows^^ on the 

 striped cucumber beetle and the cucurbit wilt organism. They proved that the 

 bacillus will remain viable for at least six weeks when the insect is hibernated in 

 cold storage. 



The writer has attempted to recover the spores of late blight from over- 

 wintered potato beetles but has thus far been unsuccessful. 



Conclusion 



It will be observed that in the case of the beet leaf-hopper, in the body of 

 which the curly-leaf organism undergoes some sort of development, infection is 

 practically certain. Almost equally certain is infection from sucking insects 

 which, shortly after feeding on some plant infected with a bacterial disease, attack 

 a healthy plant, or from such forms as Diahrotica which feed equally freely on 

 diseased and on healthy plants. Those insects which merely carry the germs from 

 tree to tree or make wounds which may serv'e as points of infection are not as 

 important a factor in the spread of disease as those which directly inoculate the 

 plants, because of the greater elements of chance which enter into the probability 

 of infection with disease thus conveyed, but their importance can not be disre- 

 garded. 



The cases cited above do not cover the entire field of exact observation or 

 experimental evidence on the agency of insects in transmitting plant diseases, 

 nor do they touch upon the numerous suspected carriers, but they are sufficient 

 to show the very important part insects can and do play in the dissemination of 

 some of the most destructive plant pathogens. The annual loss caused by insects 

 is usually estimated at about ten per cent, of the total crop value, but to this 

 should be added the very considerable loss which they indirectly cause by spread- 

 ing disease among plants. 



A consideration of the part played by insects in the dissemination of plant 

 diseases makes it clear that a large number of the most serious fungus diseases 

 can be more effectively controlled by insecticides than by fungicides. This 



" Rand and Enlows. Loc. Cit. 



