618 ANNUAL REPORTS OF DEPARTMENT OP AGRICULTURE. 



WORK AGAINST THE GIPSY MOTH AND THE BROWN -TAIL MOTH. 



It was pointed out in the last rc'])ort that a most important series 

 of experiments had been begun with regard to the rehitive resistance 

 of native trees to the attack of the gipsy moth. This work has been 

 continued. Tt was shown that ahliough tlie listed food plants for 

 the gipsy moth included almost all oi" our native plants, it is be- 

 ginning to be found out that certain species are resistant and even 

 immune to the young larvae. Experiments were detailed whereby, 

 after the removal of favored food plants, a 17-acre tract of chestnut 

 was perfectly protected, and in the same way that in another experi- 

 mental tract of coniferous trees the removal of the favored food 

 plants, particularly scrub oak and birch, left the valuable forest un- 

 attacked and practically immune. The basic idea of this work and 

 that which has been subsequently carried on, and which must con- 

 tinue for some time, is to develop a system of forest management 

 which will obviate the forest stripping which is now going on in the 

 mixed forests of parts of New England and to protect in a large 

 measure by this very system the stand of the trees. 



Over 250 localities have been selected in different parts of Maine, 

 New Hampshire, and Massachusetts, where different conditions of 

 infestation exist. These places are being carefully examined from 

 time to time in order to determine the increase of the species under 

 varying conditions and to secure a more thorough knowledge of the 

 feeding habits of the caterpillars. In the laboratory 50 different 

 kinds of trees and shrubs native to New England are being used in 

 feeding tests, and a number of other tests are being carried on to 

 determine the behavior and development of the caterpillars when 

 the woodland is thinned to clean stands of different species of trees. 

 It w^ill be necessary for the outdoor experiments to be continued 

 for several years in order to obtain exact data, but it is already per- 

 fectly plain that the information gained in this way will have a direct 

 bearing on the proper methods of thinning w^oodland in order to 

 prevent serious gipsy-moth devastation, while it will also guide in 

 forest planting; and, moreover, data which are gained in these ex- 

 periments will determine the rate of reproduction under normal con- 

 ditions for comparison with the rates in places where parasites have 

 been liberated in the fields. 



The actual work of the bureau in preventing the spread of the 

 gipsy moth and the brown-tail moth has been carried on in the same 

 way as in previous years. The apparent increase in the area infested 

 by the gipsy moth has been less than in any years since 1905. The 

 newly infested area in Maine is greater than that in all of the other 

 States together. The spread there is attributed principally to the 

 carrying of the very small caterpillars by the wind. With the ex- 

 ception of three towns in western Massachusetts (Lenox, Stock- 

 bridge, and Great Barrington), all of the new colonies which have 

 been found are in towns contiguous to the previously known infested 

 area. In Rhode Island the spread has been mainly toward the south, 

 along both sides of Narragansett Bay. 



While the efforts of the bureau have been directed almost entirely 

 against the gipsy moth, the brown-tail moth has not been ignored; 

 but as its spread by flight seems to be inevitable, concentration upon 

 the gipsy moth seems desirable. 



