368 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 7 



THE RELATION OF VARIATION IN THE NUMBER OF LARVAL 

 STAGES TO SEX DEVELOPMENT IN THE GIPSY MOTH 



By F. H. MosHER and R. T. Webber 



During the season of 1912 a series of experiments on food plants was 

 carried on at the Gipsy Moth Laboratory at Melrose Highlands, Mass. 

 The main object of these experiments was to test the feeding of the 

 gipsy moth on various plants; the results to be made use of in the 

 thinning out of woodlands where this system of control could be 

 adopted. Again, the results and data thus obtained could be used 

 in comparison with this work in the field. 



The food plants chosen for these experiments included those trees- 

 and shrubs which predominate throughout the infested territory. 

 Some of the species selected were the oaks, hickories, maples and 

 birches. There were many others of more or less importance, includ- 

 ing some of the conifers, and such shrubs as witchhazel, cornus, bar- 

 berry, etc., in all about fifty different species. 



As the experiments neared completion, it became apparent that 

 there was a difference in the stages in which the larvae spun up previous 

 to pupating, and upon close examination this peculiarity seemed to be 

 more or less constant. A careful inspection of pupae indicated that 

 those larvae that pupated in the fifth stage produced male moths, 

 while those having a sixth stage developed females. 



As there was little data at hand to show the constancy of this 

 variation the results were noted and conclusions reserved until a later 

 period. 



The following year, 1913, the feeding experiments were repeated 

 and the same method used as during the previous year, except that 

 a more careful system of record keeping was devised and more atten- 

 tion was paid to the stage and pupation of caterpillars. 



Method of Conducting Food Experiments 



Under the single head of food plant experiments were grouped the 

 following sub-experiments : 



(1) The continuation of last year's experiments in which the eggs 

 laid by the parent moth reared on a single food plant, were hatched 

 and their progeny placed on the same food plant as last year. 



(2) The combination food plant experiments in which the newly 

 hatched larvae were placed on a combination of foods and reared in 

 that manner. 



(3) Straight food plant experiments in which newly hatched larvae 

 were reared on a single food plant. 



