INSECTS AND THE SPREAD OF PLANT DISEASES^ 



By Waxtee Cabteb 

 Pineapple Experiment Station, Honolulu, T. H. 



[With 6 plates] 



Insects are recognized as important factors in agriculture on 

 account of their direct attack on plants. Grasshoppers may appear 

 in clouds that darken the sun and devour every living green plant 

 in their path. Cutworms, living underground, may devastate a 

 farmer's wheat field by pinching off the young seedlings as fast 

 as they sprout. 



Insects are also recognized as injurious to man's health, either by 

 direct attack or as carriers of agents of diseases. One familiar ex- 

 ample will suffice for both; everyone has experienced the sharp 

 probing mouth parts of the mosquito, and nearly everyone is aware 

 that if the mosquito is carrying the organism of malaria, its bite 

 is infinitely more dangerous. 



The third manner in wliich insects may vitally affect man's ac- 

 tivities is as carriers of disease organisms or as agents of plant 

 diseases, and in recent years it has become increasingly evident that 

 some of the most difficult problems of entomology are those in which 

 both insect and plant disease are concerned. 



There are three ways in which an insect may be involved : First, 

 the insect may carry on, or in, its body the spores of fungi and 

 bacteria, and contaminate blossoms or wounds on the plant with 

 these organisms. Second, the insect may feed by puncturing the 

 leaf or stem and sucking the plant jucies. In so doing the insect 

 injects fluids into the plant, which facilitate the feeding process, 

 and these fluids may have a profoundly disturbing effect on the 

 plant. In such cases the insect itself is the source of the agent of 

 disease and no organism is involved. Third, the insect may acquire 

 from a diseased plant, and transmit to other plants, minute bodies 

 called viruses, which may or may not be living tilings. 



* Published with the approval of the Director as Miscellaneous Paper No. 30 of the 

 Pineapple Exjjeriment Station, University of Hawaii. 



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