32 
THE BEAX THEIPS. 
leaves of wild lettuce were collected on April 7 and they had a 
number of eggs in them very recently laid. The last of these hatched 
on April 24, making the length of incubation about 17 days, or possi- 
bly as many as 21 days. The average mean temperature for these 
21 days was 59.1° F. 
In July several adults of this thrips were confined over night on 
leaves of growing plants that were uninfested, and were removed 
on the following morning. In this way a number of eggs were ob- 
tained that hatched under absolutely normal conditions, as the plants 
were kept in an open-air insectary. 
Table IV has been prepared to show the records of incubation for 
these eggs. 
Table IV. — Length of egg stage of the bean thrips in July at Compton, Cal., 1911. 
Date of 
Dates eggs hatched and number each day. 
First egg 
hatched. 
Last egg 
hatched. 
Shortest 
incuba- 
tion. 
l 
Longest Total 
incuba- eggs 
tion. hatched. 
ovipo- 
sition. 
Julv 
23/ 
Julv 
24/ 
Julv 
25/ 
July 
26. 
July July 
27. 28. 
July 
29. 
July 
30. 
July 10 
July 11 
5 
54 
26 
16 
18 
3 
9 
2 6 
7 1 
July 23 
Julv 24 
July 28 
Julv 28 
July 27 
July 29 
Days. 
13 
13 
13 
Days. 
18 86 
17 60 
July 14 
8 
15 
14 23 
169 
In this experiment 169 eggs hatched and the minimum length of 
incubation was 13 clays and the maximum 18 days, but nearly 50 
per cent hatched in just 14 days. During this total period the aver- 
age mean temperature was 69.6° F. 
Again, on August 20 adults were confined over night on a living 
plant of wild lettuce, and 4 larva? hatched on September 4, and 7 on 
September 5, making the periods' of incubation 15 and 16 days. 
During this time the average mean temperature was 66.3° F. 
During the months of October and November the incubation is 
probably lengthened a few days and will take about 21 days, as the 
average mean temperature for these months was, respectively, 58.67° 
and 55.3° F. 
THE LARVA. 
The length of time occupied by this insect in the larval stage dur- 
ing the months of March, April, and May was observed during the 
year 1911 by confining larva? that had just emerged in vials con- 
stantly supplied with fresh food. Table V gives the results of these 
observations. While in the first part of this period the length re- 
quired was from 17 to 19 days, later it was shortened to 9 and 11 
days. The average mean temperature for the first period, March 
19 to April 7, was 61.5° F. and for May 14 to May 27 it was 61.1° F. 
