19 
extended over two years, that a consistent temperature in the neigh- 
borhood of 18° F. will not destroy the larve of Tineola biselliella or of 
Attagenus piceus, but that an alternation of a low temperature with a 
comparatively high one invariably results in the death of the larve of 
these two insects. For example, if larve of either which have been 
kept at a temperature of 18° F. are removed to a temperature of from 
40° to 50° F. they will become slightly active, and when returned to the 
lower temperature and kept there for a little time will not revive upon 
a retransfer to the warmer temperature. 
It is thus rather satisfactory to have experimental proof in support 
of previously accepted but more or less theoretical ideas. 
Mr. Poulton stated that he had long held the opinion that an alter- 
nation of high and low temperatures frequently played an important 
part in the outbreaks of injurious insects. 
Mr. Rolfs had noticed that after severe frosts and cold in Florida 
there was an abundance of northern insects, especially Orthoptera. 
Mr. Craig described the severity of the winter of 1896-97 in Canada, 
when there was severe cold but little snow. This year, throughout 
southern Canada, plant-lice were present in tremendous numbers on 
apple, plum, cherry, and other trees. 
In the general discussion which followed the fact was brought out 
that plant-lice had been particularly abundant throughout Canada and 
the United States during the past summer. 
Mr. Howard pointed out the fact that this abundance was probably 
due to the wet weather of late spring and early summer, which had 
checked the feeding and multiplication of the natural enemies of the 
plant-lice. 
Mr. Minot stated that in the vicinity of Milton, Mass., injurious insects 
had been quite scarce during the past summer; fewer potato beetles 
had been noticed than for many years, while rose-chafers and tent cat- 
erpillars were equally scarce. He also had noticed the great abundance 
of plant-lice early in the season, but after the extreme hot weather of 
the first week of July their numbers greatly diminished. 
Mr. Howard emphasized the fact that hot weather played a very 
important part in controlling plant-lice. He cited an instance where, 
several years ago, Mr. Barrows had called his attention to the extraor- 
dinarily large number of plant-lice upon certain shade trees of Wash- 
ington, D.C. The following day the temperature reached the maximum 
of 101° F., and as a result the plant-lice disappeared like magic. 
Mr. Ashmead called attention to the fact that the family of plant-lice 
was not extensive in the Tropics, thus supporting the theory previously 
discussed. 
Mr. Barrows stated that the condition in Michigan regarding plant- 
lice was probably the same as that in Canada. He was of the opinion 
