INJURIOUS AND BENEFICIAL INSECTS OF CALIFORNIA. 



4!):: 



THE COMMON NEMATODE OR POTATO EELWORM " 

 Ueterodera radicicola Greef 



(Figs. 489, 490) 



Eel worms belong to a phylum of animals far below insects and are 

 never considered in a general work on entomology, but, due to the 

 seriousness as well as the wide distribution of this worm as a pest of 

 crops, a brief account of it is herein included. 



Description. — The presence of this pest is told by such characteristic 

 injuries as root knot on nursery trees, galls on the roots of tomato vines 

 and the rough, warty surface of potato tubers (Fig. 490). The animal 

 causing the injuries is com- 

 monly known as the nematode 

 and was recently given much 

 prominence as the potato eel- 

 worm. The males and young, 

 the usual forms of the animal, 

 are microscopic, transparent 

 and shaped much like minute 

 eels. The female is pear- 

 shaped and pearly - white 

 (Fig. 489). The eggs are 

 oval in shape and laid in 

 great numbers. 



Life History. — The young 

 eelworms feed upon the roots 

 of various plants, causing 

 galls or knots which may 

 greatly impair growth. The 

 female develops within the 

 affected areas and begins egg- 

 laying, the eggs hatching in a 

 very short time. The winter 

 is passed in the original host, 

 such as nursery stock, if it 

 remains growing in the soil, but if the host is removed they feed upon 

 various plants left in the fields. The young have the ability to encyst 

 themselves so as to resist great extremes of weather and unfavorable 

 conditions, so when once established in the soil it is very difficult to 

 eradicate them. 



Nature of Work.— These minute worms, working into the roots of 

 plants, produce very characteristic galls or warts and cause what is 

 commonly known as root knot. 



Distribution.— As a producer of root knot this animal is very com- 

 mon throughout the State, but somewhat more abundant in the central 

 and southern parts. As a potato pest it has been reported only from 

 Alameda, Contra Costa, Inyo, Los Angeles, Monterey, Sacramento, San 

 Joaquin, Santa Barbara and Tulare counties. 



33 sChilds, Leroy, Mo. Bui. Cal. Hort. Com.. II. pp. 737-756, 1913. 



Bessey, Dr. E. A., Bui. No. 217, Pur. PI. Ind., U. S. Dept. Agric, 1911. 



Fig. 489. — Female bodies of the common 

 nematode or potato eelworm, Heterodera 

 radicicola Greef. Enlarged live times. (Photo 

 by Leroy Childs) 



