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A NOTE ON ORGYIA VETUSTA. 41 



A Note on Orgyia vetusta. 



By T. A. CHAPMAN, M.D., F.R.S. 



Towards the end of 1917 Dr. J. W. H. Harrison gave me three 

 egg masses of Orrpjia vetusta, a Californian species. They were a 

 large and two smaller ones. 



During May, 1918, and on into June 7tb, over 400 larvse hatched. 

 I did not note the first day of hatching, but o.n June 7th I thought 

 they must nearly all have hatched, as the emergences were falling 

 off, and some larvse were well grown in their third instar. By the 

 9th, however, 32 more larvae had hatched, between the 9th and 11th 

 35 appeared, and they continued hatching for another month ; the 

 numbers being — 



June 9th, 32; 11th, 35 ; 13th, 46, one is now in 4th instar ; 15th, 

 20 in last two days ; 17th, 24 ; 19th, 29 ; 21st, 19 ; 23rd, 19 ; 25th, 

 11 ; 27th, 10, at this date the earliest larvte spun up in 5th instar ; 

 29th, 6 ; July 1st, 8 ; 3rd, 3; 5th, 1 ; 7th, 2; 9th, 3 ; 11th, 1 ; 13th, 

 4, the last to hatch. Total, 273. 



The long period over which the hatching spread, about ten weeks, 

 is quite parallel to that of 0. antiqita, making many observers believe 

 that; species to be double-brooded ; this is the case more or less in the 

 South of Europe, but in the British Isles, never. Well, hardly ever ! 



The dates of spinning their cocoons were taken roughly, by taking 

 the cocoons in batches a few da,ys after each lot was completed, 

 largely with the view of finding relative dates for male and female 

 larvae, spinning up. 



The first larva to spin up did so on June 27th. By July 10th a 

 number had done so, and had monlted to pup^e, so that the sexes were 

 unmistakable, and afterwards a census was taken, as convenient, as each 

 lot reached this stage. > 



The results were as under — » 



The spinning occupied two months. The 5th and 6th lots, and 

 again the 8th and 9th, should probably be taken together, as I think 

 they were affected by my separating the larvae with a view to detect 

 whether the females moulted once more than the males. It is obvious 

 that the males spun . up sooner than the females, not because they 

 hatched earlier, but because they had lessjeeding to do. 



? ? 



1 



7 



38 



2 



77 



60 



31 



87 



2 



30 



38 



5 



4 



4 



Totals ... 327 336 



March 15th, 1919. == = 



