10 BULLETIN 421^ U. S. DEPARTMENT OF AGEICULTURE. 



reached in the middle of the day. The average mean temperature 

 was about 73° F. during the time of development. 



The egg requires from 12 to 14 days to develop; the nymph molts 

 four times, the first instar lasting about four days. The second stage 

 transforms to the third in about eight days. The third stage is short, 

 the skin being molted in about a day. The fourth or last stage 

 requires about five days before it emerges as an adult. 



The full length of the adult's life was not determined, but adults 

 emerging from isolated pupae on February 11, 1916, were still alive 

 40 days later. 



The normal mode of reproduction is bisexual, but owing to the 

 fact that at certain intervals the proportion of males to females is 

 very small, it is likely that parthenogenesis occurs as in other species 

 of this group. While this species was under observation males were 

 present most of the time, but in very small numbers, although on one 

 occasion they appeared very abundant, nearly equaling the females. 



CONTROL. 



In the greenhouse the sugar-beet thrips may be held in check by 

 the apphcation of a strong spray of water to the foliage. This 

 washes the younger stages from the leaf; and as these are unable 

 to reach the food plant again, they die. 



As a result of experiments, spraying is the best method of control, 

 both in the greenhouse and out of doors. The following solutions 

 were used : 



Experiment No. 1. 



Nicotine sulphate ounces. . 4 



Fish-oil soap -. pounds. . 4 



Water gallons. . 50 



Result: About 60 per cent of adults and 40 per cent of nymphs 

 kiUed. 



Experiment No. 2. 



Nicotine sulphate ounces. . 5 



Fish-oil soap pounds. . 4 



Water gallons. . 50 



Result: Ninety per cent of adults and, 60 per cent of nymphs 

 killed. 



Experiment No. 3. 



Nicotine sulphate ounces. . 6 



Fish-oil soap pounds. . 4 



Water gallons. . 50 



Result: All adults and about 95 per cent of njnnphs kiUed. 



The fact that the adults were more susceptible to the spray than 

 the nymphs may be due to the globule of excretion which serves to 

 protect the body of the nymph. 



