1910.] PUBLIC DOCUMENT — No. 31. 75 



ally done in this locality, and then treated with a mixtnre of 

 Paris green and dnst until a greenish color is perceptible, it will 

 not be eaten by wire worms. These experiments will be repeated 

 the coming year. 



Within the last twenty years Massachnsetts has been in\'aded 

 by several injnrions insects which naturally belong farther 

 sonth. Among these may be mentioned the elm-leaf beetle, San 

 Jose scale, common asparagus beetle and the twelve-spotted 

 asparagus beetle. How far north these pests can spread and be 

 injurious is as yet unknown, but it is certain that there are 

 Ji'mits to this spread, and for at least some of those named it 

 seems quite certain that these limits may probably be found 

 within this State. It is not a ])articular degree of latitude 

 which marks the barrier to their further spread northward, l)ut 

 rather climatic conditions, and these are modified by elevation. 

 In other words, the limiting lines of distribution appear to be 

 isothermal in their nature, though their exact character is as yet 

 unsettled. It may be the average winter temperature, the mini- 

 nnim winter temperature or some other factor which settles 

 whether an insect shall be a pest at an}' given place near its 

 northei-n limit. In any case, the determination of this cause, 

 and the resnlting couclusion that an insect will or will not 

 become injurious at a given place, will be of much importance. 

 As an example of this it may be stated that such evidence as is 

 now available, though as yet too little to be conclusive, suggests 

 the belief that in Massachusetts the elm-leaf beetle will not be 

 likely to be of much importance in those parts of the State 

 which are more than a thousand feet above sea level, except, 

 perhaps, near the southern edge of the State, where the altitude 

 is to some extent offset by the more southern latitude. To work 

 out problems of this nature fuller meteorological data are needed, 

 as well as more observations of the distribution of the insects 

 themselves, and studies of this kind have been in progress for 

 several years, and wnll be continued. 



Parasitism as one of nature's methods for the control of in- 

 jurious forms has long been recognized. It has been utilized 

 in numerous cases by man, w^ho has conveyed parasites from one 

 country to another to attack their hosts, which have already been 

 by accident thus transferred. Perhaps the most gigantic experi- 



