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 larva? the trays measured 6^ by 6f by 

 2 inches, and trays 12^ by 12^ by 2-| inches (all inside measure) (PL 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 larvae 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 (PL 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 quickly 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 traj 7 s 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. In 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 as a number of retests and special 

 experiments were conducted each year, 150 trays were in use continu- 



