1974] 
Cooper — Boreus 
105 
Fig. 4. Head of last instar Boreus notoperates. A, frontal view. B, 
mouthparts in ventral aspect. For details see text. Full scale = 0.4 mm 
for A, = 0.2 mm for B. 
The number of larval ecdyses is not known for any species of 
Boreus , but it is very likely four as in other species of Mecoptera 
(Currie 1932, Setty 1940, Byers 1963). The ratio of the mean head 
length of the larger larvae and pharate pupae to that of the smaller 
larva is 1.38. This gives estimated head lengths for the two im- 
mediately preceding larval stages as 0.36 mm and 0.26 mm respec- 
tively. As the head length of the first instar larva is known to be 
O.32 mm, the series ends there and the number of instars is thus 
very likely four. The probable Dyar constant of 1.29 (which is low 
compared with Byer’s figure of 1.46 for Panorpa nuptialis) gives a 
calculated head length of 0.41 mm for instar-2, of 0.49 mm for 
instar-3, and of 0.68 mm for instar-4. Striibing (1950) left the 
matter of the number of larval instars of B. hyemalis open. Withy- 
combe (1922), also unable to find larval exuvia, judged from head 
capsule growth that there are at least four instars. Though Striibing’s 
measurements of larval head capsules are in fact heterogeneous, they 
are reasonably well satisfied by a Dyar constant of 1.34 and four 
instars. 
The full grown larva of B. notoperates is remarkably similar to 
the first instar larva (compare figs. 3D and F). The head is pale 
amber in color, the body white to pale yellow, and in life it ranges 
from 2. 6-3. 7 mm in length. In shape it is “scarabaeiform,” to use 
Peterson’s (1951) characterization of the larva of B. brumalis. As 
