1915 ENTOMOLOGICAL SOCIETY. 117 



VARIATIO^T IN THE COLOUE OF THE BRISTLES OF THE HEDGE- 

 HOG CATERPILLAR, ISIA ISABELLA S. and A. 

 AUthur Gibsox, Chief AssISTA^TT Entomologist, Department 

 OF Agriculture, Ottawa. 



For some years the writer has been interested in the remarkable variation in 

 the colour of' the larval bristles of the arctian, Isia isahelJa S. and A., and an en- 

 deavour has been made to obtain a series of the mature larvas in colours, ranging 

 from wholly red to wholly black. This series is not as yet quite complete, but it is, 

 I think, of sufficient interest to present at this meeting. As almost everyone knows, 

 in most specimens the colour of the bristles from the central segments is a rust-red, 

 the remaining bristles being black. For some time I have had specimens in which 

 the red bristles predominated, and one example in which almost all of the bristles 

 were rust-red, luit it was not until the spring of 1914 that a larva almost wholly 

 black was obtained. This latter specimen was received from British Columbia, 

 along with examples of the more ordinary type. The larvae were unusually abund- 

 ant in that province and attracted considerable attention, owing to their well known 

 habit of .wandering about in spring preparatory to pupation. 



A study of the colour of the bristles of the specimens shown herewith, indicates 

 as folloAvs : — • 



Specimen No. 1. — This example has nearly all of the bristles from the tubercles 

 of a bright rust-red, the exceptions being a few black bristles from the lateral tuber- 

 cles on segments 2, 3 and 4, and a few from dorsal tubercles on segment 2. 



Specimen No. 2. — The bristles on this specimen are rust-red from all segments 

 excepting those on segments 4 and 5, and a few from segments 2 and 3, which are 

 black. 



Specimen No. 3. — From segments other than 3, 4 and 5, and a few from dor- 

 sum of segment 12, the bristles are rust-red. 



Specimen No. Jf. — The black bristles on this larva are from segments 3 and 4, 

 and on dorsum of segments 12 and 13, and a few from lateral tubercles on anal seg- 

 ment; tne others rust-red. 



Specimen No. -S.^Bristles black from segments, 2, 3, 4, 5, 12, 13 and from 

 tubercle I on segment 6 ; other bristles rust-red. 



Specimen No. 6. — This specimen shows additional black bristles on segment 6, 

 namely, from all the tubercles excepting II. 



Specimen No. 7. — Bristles from segments 2, 3, 4 and 5 wholly black, from seg- 

 ment 6 mostly black, few rust-red bristles from tubercles II and III, and about half 

 of this colour from tubercle IV. The bristles on the dorsum of segment 11, from 

 tubercles I, II and III, and all from segments 12 and 13 are also black. 



Specimen No. S. — This larva differs from No. 7 in having all the bristles on 

 segment 6 black, and only rust-red bristles from tubercles VI, VII and VIII on seg- 

 ment 11. • 



Specimen No. P.— From all tubercles on segments 2, 3, 4, 5, 6, 12 and 13 the 

 bristles are black ; the others rust-red. 



Specimen No. 10. — In this lan^a the black bristles are from the same segments 

 as is the case with No. 9, but in addition all the (bristles from tubercle I on segment 

 7, and from tubercles I, II and HI on segment 11 are also black. 



Specimen No. 11. — The only rust-red bristles on this specimen are from seg- 

 ments 8 and 9. 



Specimen No. 12. — Almost wholly black, only a few very dark reddish-brown 

 bristles from lateral tubercles, particularly on central segments. 



