﻿22 BULLETIN 1357, U. S, DEPARTMENT OF AGRICULTURE 



collected 8 to 10 inches from the main stem of a plant, and at a depth 

 of 6 to 7 inches from the surface. Usually they are found at a depth 

 of 2 to 3 inches, and as many as 19 specimens have been found 

 among the roots of a single plant. 



, FEEDING HABITS 



Although their first attention seems to be given to the smaller 

 feeding rootlets, the larvee also gnaw and penetrate the main roots. 

 (Fig. 2.) They have been observed to girdle the crowns just below 

 the soil surface, resulting in the loss at one establishment of over 

 100 " own-root " plants which had been set about three months pre- 

 viously.' Older bushes can withstand more severe feeding before 

 showing the effects. Plants in a decidedly poor condition had been 

 growing in a bed for five years and showed many furrows in the 

 main roots which had evidently been the source of larval nourish- 

 ment. Only a few new growths were produced after " pinching " 

 the shoots, and these were short and weak because the vitality of the 

 plants was very low, and the foliage lacked its normal green color. 

 These plants were used for experimental work on the soil stages 

 and accurate counts were made of the number of larvae and pupse 

 found in each. During the examination of 481 of these plants 2.991 

 larvffi and pupee were found, or an average of 6.22 to a plant, the 

 maximum being 23 specimens. 



Examination made in August, 1921, of the roots and soil around 

 58 plants dug up at random in different sections of a greenhouse 

 Avhere 3,000 plants were being removed, showed that 130 larv^ and 

 150 pupae were present, or an average of 4.8 specimens of the soil 

 stages to each plant. If this condition prevailed throughout the 

 house it would mean that there were 14,400 individuals in the soil at 

 that time. Since egg laying is continuous throughout the spring and 

 earlj summer months, the roots of these plants had probably iDeen 

 subjected for several months to attacks by successive large broods of 

 larvae. 



A comparative lack of the fresh white feeding rootlets was con- 

 spicuously evident in the case of the infested plants mentioned above. 

 Even though very few of the older plants die as a direct result of 

 the larval attack, they become so weakened that many of them fail 

 to witlistand the rigorous treatment accorded the bushes when sub- 

 jected to artificial dormant conditions. It is a cultural practice 

 among the growers during the drying-off period to withhold watei" 

 from the plants for a period of from two to four weeks or longer, 

 after which the greater part of the growth is pruned off until onty 

 from 12 to 18 inches of the main stems are left. Moisture is again 

 made available to the roots, and normal plants will immediately put 

 forth new growth from the buds. Extensive injury to the root 

 systems (fig. 2) prevents them from functioning normallj^ and re- 

 sults in the loss of the more severely injured plants. 



In less than three dajs 23 newly hatched larvae confined in a vial 

 with soil containing roseroots chopped in half-inch lengths have 

 eaten the equivalent of 10 inches of roots which were approximately 

 one-sixteenth to three thirt37--seconds of an inch in diameter. In 

 several instances where pupae were kept in the same cage they were 

 chewed bv the larvae. That the larvae are able to burrow through the 



