DISPEESION" OF GIPSY-MOTH LAEV^l BY THE WIND. 15 



secured on those at Hillsboro and Troy, N. H., the infestations in 

 the neighborhood of which were fewer and at longer distances. 



In 1912 several large gipsy-moth colonies were found in Andover 

 and Henniker, N. H. On Beech Hill, Andover, about one-third of a 

 mile from where the screen was erected, over 30,000 larvae were 

 destroyed in the summer of 1912. This colony and surroundings 

 were carefully treated, so that the infestation was nearly extermi- 

 nated in 1913 and 1914. All the smaller colonies found in the town 

 also received thorough treatment. Similar conditions prevailed in 

 Henniker. 



The screens were examined at periods during the dispersion season 

 of 1913 and 1914. No positive results were secured during the first 

 year, but one living larva was removed from the Andover screen 

 May 27, 1914, at 2 p. m. 



May 26, 1914, a dead larva was removed from the Henniker screen 

 and a living specimen June 13, together with the molted skin of a 

 second-stage larva. It is difficult to state from which direction the 

 first larva was blown, but the second came from the northwest or 

 west as the wind blew from those directions during the two days 

 previous. 



The 3 first-stage larvae caught on the Andover and Henniker 

 screens in 1914 proved conclusively that the dispersion among the 

 hills is brought about most extensively by the wind. This is more 

 emphatic when one considers the small air space covered by these 

 traps and the small sources of infestation in these localities. 



ALTITUDE EXPERIMENT WITH AVIATION OF SMALL CATERPILLARS. 



At the close of the season's work in 1913, after securing some fair 

 records on the distance that larvae are borne by the wind, it seemed 

 advisable to get data on the possible altitude they reach during their 

 transportation. After numerous inquiries and investigation a suit- 

 able place for such an experiment was found in Merrimac, Mass. 

 (PL VII). This consisted of the standpipe (PL V, fig. 1) for the stor- 

 age and pressure of the town water. It is located on a small hill 240 

 feet above sea level, and permission to erect a small wire screen on 

 the top oi the tank was obtained from the selectmen of the town. 



The tank was 55 feet high from the level of the summit of the hill 

 and a screen of |-incb mesh poultry wire was stapled to upright 2 by 4 

 posts 5 feel Long. The top selvage of the wire (PL V, fig. 2) was 5 

 feet above the top of the Imik, totaling 00 feet above, the ground. 

 The screen was 36 feet Long and contained Ml square feet, while the 

 tank was 40 feel in diameter, allowing ample space for the examiner 

 to gel around the ends. It was set up so that the sides faced the east 



and v, 



