GIPSY MOTH WORK IN NEW ENGLAND. 13 



This work has been carried on at the Bussey Institution, Forest 

 Hills, Mass., and a sublaboratory in charge of Mr. J. J. Culver has 

 been maintained during the summer at Worcester, Mass., where 

 special experiments have been conducted to determine the relation of 

 favorable and unfavorable food plants to the development of the 

 disease. A series of field experiments was also conducted in a selected 

 area at Lunenburg, Mass., by Mr. A. W. Young and Mr. K. T. Webber, 

 who made continuous observations in a limited area on the develop- 

 ment of the disease under field conditions, with particular reference 

 to the relation of temperature and humidity. Several other points 

 were selected in Massachusetts where continuous temperature and 

 humidity records were secured, as well as at the Lunenburg area, 

 and a careful compilation of this data is expected to give informa- 

 tion as to the weather conditions which are most favorable for the 

 development of this disease. 



For a number of years the wilt disease has been found in the field 

 in nearly all places where heavy gipsy-moth infestation exists. 

 During the last year or two it has occurred in light infestations and 

 very few localities in the infested area are known where it is not 

 found to a greater or less extent. 



The results of the season's work indicate that the disease has been 

 slightly less prevalent during the past summer than the previous 

 year and this was particularly true during June and the first part of 

 July. Cool weather prevailed at this time. Late in July the large 

 caterpillars in many places were seriously affected, so that the in- 

 crease of the gipsy moth was not as great as was anticipated early 

 in the season. 



The technical studies on the wilt disease are very difficult to con- 

 duct because it is almost impossible to secure healthy material for 

 experimental purposes. The organism is believed to be a filterable 

 virus and is so minute that it easily passes through the finest bacterio- 

 logical filters that have yet been devised. It belongs to the same 

 class of organism as yellow fever and a number of other contagious 

 diseases, although all of these were, at one time, supposed to be 

 caused by bacteria. The period when gipsy-moth caterpillars of 

 moderate size are available for experiments covers about six weeks, 

 and this adds to the difficulty of carrying on investigations on account 

 of the limited time when material can be secured. During the past 

 year it has been determined that the wilt disease, or a similar organ- 

 ism, affects eight of our common native caterpillars in addition to 

 the gipsy moth. It is also known to attack the silkworm (Sericaria 

 mori L.) and nun moth (Porthetria monaclia L.), a fairly common 

 European species which is very destructive to pine. Good results 

 have been secured this year, but a large amount of work is necessary 



