258 INSECT PESTS OF FARM, GARDEN AND ORCHARD 



When the grubs are noticed in the plants, a good allowance of fer- 

 tilizer will do much to quicken growth and thus enable them to 

 mature a crop. 



The Potato Tuber-worm * 



The most serious pest of the potato in California is the Tuber- 

 worm, which in tobacco regions of the Southern States is known 

 as the " split worm " or leaf -miner (see page 223). Not infre- 

 quently 25 per cent of the crop is lost in infested regions in 

 California, injury occurring both in the fields and to the tubers 

 in storage. As the pest is carried in the potatoes and breeds in 

 storage throughout the warm winters of California, and when 

 exported across the Pacific, it is necessary to inspect closely 

 potatoes from infested regions. Although no injury to potatoes 

 has occurred outside of California, and though the insect probably 

 could not exist in the North, it may well be guarded against in 

 the Southern States, where it is a common tobacco pest.f 



Moths which have developed from larvae working in stored 

 potatoes are on the wing when young potatoes are up, and lay 

 their eggs at the base of the leaves. The young larvae bore into 

 the stalks, often causing the plants to wilt and die. On older 

 plants or when the stalks harden, the larvae leave the stalks and 

 enter the tubers, particularly where they may be exposed. - Where 

 potatoes are exposed by being insufficiently covered the moths 

 will lay their eggs directly upon them, as they also do upon po- 

 tatoes exposed in the field after digging. 



Most of the observations upon the life history seem to have 

 been made upon the insect when breeding in stored potatoes. 

 The eggs are about one-fiftieth inch long, oval, white, and laid 

 singly or in pairs, about the eyes of the potatoes, or in similar 

 rough places, where they are seen with difficulty. They hatch 

 in a week or ten days, and the young larvae are about one-twenty- 

 fifth inch long of a transparent white color. The larvae burrow 

 beneath the skin and bore into the potatoes, filling their 

 burrows with grass and excrement, which soon give rise to various 

 rots which cause the destruction of the tuber, already rendered 

 unfit for food by the burrows. The larvae become full grown 



* Phthorimasa operculella Zell. See W. T. Clarke, Bulletin 135, California 

 Agr. Exp. Sta. Also J. E. Graf Bulletin 427, U. S. Dept. of Agr, 



t Recently serious injury by this insect has been reported to potatoes 

 near Hallettsville, Texas. 



