INSECTS AS VECTORS OF PLANT-PATHOGENIC FUNGI 4i3 



causing elephantiasis of man, that the malaria-producing protozoa 

 are transmitted by mosquitoes, and that ticks transmit the Texas 

 cattle-fever organism. Furthermore it had been established that 

 the bacterium responsible for fire blight of pears and apples may 

 be dispersed by bees and wasps. From such basic observations on 

 insect transmission of nematodes, protozoa, and bacteria respons- 

 ible for animal and plant diseases, interest in insects as vectors 

 increased. As an outcome, instances were found and convincing 

 proofs were submitted that viruses and plant-pathogenic fungi 

 may also be dispersed by insects. 



The dispersal of plant-pathogenic fungi by insects is accom- 

 plished quite fortuitously. Spores that adhere to the body of the 

 vector may become dislodged on a near-by host. Leaf-eating in- 

 sects quite generally consume diseased and non-diseased tissues 

 indiscriminately, and the spores may pass intact through the ali- 

 mentary tract. Such spores in the fecal matter can then serve as 

 inoculum. Again, spores may be introduced or may gain entrance 

 into plant tissues, especially of fruits and twigs, through incisions 

 made in connection with oviposition. 



In general, all the dispersal of spores of a given fungus is not 

 accomplished by one species of insect. Rather several species of 

 insects serve as vectors; they may belong to entirely different 

 groups. Among the kinds of insects known to be vectors of plant- 

 disease-producing fungi are grasshoppers, crickets, aphids, scale 

 insects, beetles, true bugs, flies, wasps, and bees. 



As might be anticipated, abundance of a given vector may be 

 directly correlated w T ith the severity of an outbreak of disease 

 among plants. For this reason insect control and plant-disease 

 control sometimes become mutually interdependent. 



Among important plant-pathogenic fungi known to be trans- 

 ported by insects are the following: Endothia parasitica, the chest- 

 nut-blight fungus, Claviceps purpurea, the ergot-producing organ- 

 ism, Phoma lingam, the cause of cabbage blackleg, Nematospora 

 phaseoli, the cause of pod spot of Lima bean, Septoria ly coper sic'u 

 the cause of a leaf spot of tomato, Sclerotinia fnicticola, the 

 brown-rot fungus of stone fruits, Botrytis anthophila, the cause of 

 clover-blossom blight, Ceratostomella uhni, the Dutch elm patho- 

 gen, and C. pilifera and related blue-stain-producing species on 

 coniferous wood. 



