PROC. ENT. SOC. WASH., VOL. 20, NO. 1, JAN., 1918 17 



The writer remembers his disappointment when, upon first 

 becoming interested in entomology, he had the good fortune, as 

 he then regarded it, of having a fine lot of larvae of the common 

 luna moth. Upon having to move to another locality, and not 

 finding the food plant available upon which the colony was being 

 fed, he changed to another food plant which the text books said 

 was also a customary food for this species. The colony flourished 

 and in time a goodly number of cocoons and, finally, of adults 

 was secured. Hoping to obtain a much larger number of speci- 

 mens, some of the moths were mated and the eggs kept for further 

 experiments, but, much to the surprise and disappointment of 

 the experimenter, none of the eggs hatched. It is of course 

 quite possible that the disastrous results in this case were due to 

 the sudden change in diet, rather than to its unsuitability, and 

 that satisfactory results might have been secured had the second 

 food been used from the beginning. 



In an experiment carried out during the past summer with 

 what appeared to be the same species of saw fly, an Argid, 

 found upon Amelanchier and also on Crataegus, a portion of the 

 larvae were in each case transferred to the other food plant. 

 It was found that, in this instance, the larvae in both cases 

 throve on Crataegus while unsatisfactory results were obtained 

 on Amelanchier. While not conclusive, this experiment is used 

 to illustrate the fact that the food plant, upon which a larva is 

 found to be feeding, may be one which will not enable the insect 

 to undergo its later transformations. 



Another series of experiments were carried on several years ago 

 with some larvae of another saw fly, Croesus latitarsus Norton, 

 which were believed to feed on two species of birch, B. lenta and 

 B. populifolia. Larvae were at this time found in great numbers 

 on the latter but none on the former food plant and some at- 

 tempts were made to rear larvae by transferring them to B. 

 lenta. It was found, in all cases, that the larvae if transferred 

 when very young would die, while if they were changed during 

 one of the later stages they could sometimes be brought through 

 satisfactorily, at least so far as securing adults is concerned. 



Such instances as those given above are probably familiar but 

 are given to illustrate certain points in regard to the question 

 of what should be considered a "food plant." Starting with a 

 case in which the larva lives for a short time only, whetherthe 

 egg be deposited on the plant itself, or whether the larva begins 

 to feed upon it in one of its later stages, we may have instances 

 in which the larva feeds upon it throughout all its stages, but 

 dies in the pupal state or, if it produces an adult, is infertile. 

 Finally we may, conceivably, have a case where for several gener- 

 ations the insect may feed upon the same food plant and then 



