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4 BULLETIN 250, U. S. DEPARTMENT OF AGRICULTURE. 
EQUIPMENT OF THE LABORATORY. 
In early spring a part of the experiments were started in the labora- 
tory, but the trays were soon transferred to a large outdoor insectary. 
It was found necessary to use canvas curtains on the sides of the 
insectary in order to shade the trays in fair weather and to prevent 
the entrance of excessive moisture and wind during storms. 
The rearing trays used were of two sizes, depending on the age of 
the caterpillars. For the small larve the trays measured 61 by 62 by 
2 inches, and trays 124 by 124 by 24 inches (all inside measure) (P1.I, 
fig. 2) were used for the larger caterpillars. These trays were of seven- 
eighths-inch dressed pine, having a narrow band of tanglefoot applied 
on the inside of the frame near the top. <A piece of cotton cloth was 
pasted to the bottom of the tray, and two clamps were attached to the 
inside to hold in place a small bottle, three-fourths inch square and 
4 inches long, provided with a crooked neck. The bottle was filled 
with water and a cork was inserted, through which was placed the 
end of a sprig of foliage, after which the bottle was secured in the 
tray by the clamp. It having developed that young larve exhausted 
themselves greatly by trying to crawl around on the cloth bottom 
of the tray, this covering was abandoned after the first summer’s 
experience and a tray made of paraffined paper (PI. II), of the 
proper size to fit into the wooden frames, was substituted. To re- 
place the two brass clamps a single elbow screw was used, which held 
the bottle firmly but allowed it to be quicklv removed. 
METHODS OF CONDUCTING LABORATORY EXPERIMENTS. 
Early in the spring, trees or shrubs to be used for a food supply 
were selected and properly tagged. Careful notes were kept of the 
condition of each, as well as the degree of gipsy-moth infestation 
upon them and upon the surrounding growth at the time the selec- 
tion was made. As soon as hatching began feeding trays were given 
the same serial numbers as the trees or shrubs that had been pre- 
viously tagged, the foliage from the same plant always being used 
in the same tray. One hundred newly hatched gipsy-moth caterpil- 
lars were placed on the foliage in each tray. The food was replen- 
ished daily or oftener if necessary, and a careful record of the num- 
ber of caterpillars that died or molted was maintained. Im cases 
where all the caterpillars died before pupation, new trays were 
started, using caterpillars one stage younger than those in the tray 
at the time it was discontinued. , 
About 60 species of trees and shrubs were tested annually at the 
Melrose Highlands Laboratory; and asa number of retests and special 
experiments were conducted each year, 150 trays were in use continu- 
