1978] 
Vetter & Rutowski — Sulphur Butterflies 
391 
same plane as the scale. The base of each scale in the sex brand 
extends beyond the point where the pedicel emerges and partially 
overlies the scale socket on the wing surface. The spacing of the 
longitudinal and transverse ridges on these scales also appears more 
variable than it is on other types of scales. 
Discussion 
Detailed information is now available about the sex brand 
morphology of five species of sulphur butterflies in the pierid tribe, 
Coliadini. They include Eurema lisa (Rutowski, 1977) and Colias 
philodice (Rutowski, 1979) as well as the three species discussed in 
this report. Several generalizations have appeared. 
1) All male sex brands are located in the friction areas of the 
wings, that is, the area of overlap between the forewings and 
hind wings. Rutowski (1979) has suggested that this placement 
of the sex brand helps to minimize evaporation from an 
otherwise exposed and non-eversible scent producing struc- 
ture. 
2) The scales observed in the sex brand are not greatly differenti- 
ated from those found in other areas of the wings. This 
contrasts with the scent scales found in many eversible scent- 
producing organs that are very hair-like (e.g. danaids (Pliske 
and Salpeter, 1971), noctuids (Birch, 1970)) and with the 
presumed scent scales on the wings of some pierids and 
nymphalids which have fringed distal borders (Barth, 1950; 
Bergstrom and Lundgren 1973; Tinbergen et al., 1942). 
3) The scales are associated with cells in the integument of the 
wing that reside in a swelling in the wing immediately behind 
the scale socket. Presumably these cells are secretory trichogen 
cells like those found in scent-producing structures that are 
histologically better known, (e.g. danaids (Pliske and Salpeter, 
1971)). 
These similarities reflect not only the phylogenetic affinities of 
these species but also the action of similar selection pressures. The 
behavior of the male during courtship is similar in all five species. 
The male buffets the female with his wings while she flies or perches 
on vegetation (Rutowski, 1978; Silberglied and Taylor, 1978; pers. 
obs.). Selection has not acted to favor any divergence from this 
pattern among these species and hence there have been no major 
