10 BULLETIN 421, U. S. DEPARTMENT OF AGRICULTURE. 
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 application 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 
killed. 
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 nymphs killed. 
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. 
