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. R. 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 heav}^ 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 (Porihetria rnonacha 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 
