Lachlan: New Gnathothlibus and Theretra sphingid moths 
81 
Discussion 
Although similar in overall appearance, the males of G. 
samoaensis are readily distinguished from G.fijiensis males 
by a variety of constant morphological differences. On the 
forewings, the prominent dark, post median oblique line that 
runs from the costa to the inner margin, is clearly straighter 
and less curved distally near the costa in G. fijiensis. The 
unicolorous median band enclosing the stigma that runs 
from the costa to the inner margin, is approximately 2-3 
mm wider, on average, on G. fijiensis. 
On the hindwings of G. samoaensis the inner edge of the 
dark terminal band is more irregular and less even than seen 
on G. fijiensis. The inner edge of this band clearly spikes 
basally along vein 1A+2A with some brown scaling basad 
along the inner margin past the tomus in almost all specimens 
examined. Neither characters appears on G. fijiensis. 
The very distinctive mauve lateral stripe on the outer edges 
of the tegulae above the wings of G. fijiensis is creamy-white 
on G. samoaensis. Immediately behind this creamy-white 
lateral stripe is a small, distinctive, patch of long orange-brown 
hair scales. These are cream to olive-cream in G. fijiensis. 
The underside of both wings of G. samoaensis are darker 
with generally more prominent post median and submarginal 
dark brown lines on the forewings than seen on G.fijiensis. On 
the underside of the thorax the ventral creamy-olive median 
band is shorter and narrower on G. samoaensis than seen on 
G.fijiensis where it is clearly longer and wider. Gnathothlibus 
samoaensis has fore-tibiae that are slightly lighter with a more 
distinctive dark, distal, ventral edge. The mid and hind legs 
are also lighter in colour than seen on G. fijiensis. 
The male genitalia of G. samoaensis. Fig. 16, differ from 
those of G. fijiensis, Fig. 14, in having the uncus, in lateral 
view, more arched, more enlarged distally with a larger, 
more robust rounded dorsal crest and a clearly smaller, more 
pointed ventral tooth at the base of the distal margin. The 
distal margin is clearly concave and not angled backwards 
as seen in G. fijiensis. The sacculus process and harpe are 
slightly larger with a thicker, upturned spike in G. samo¬ 
aensis. The upturned spike is finer and more needle-like 
in G. fijiensis. The valva of G. samoaensis differ from G. 
fijiensis primarily in having a very clear convex distal bulge 
on the dorsal margin. In G. fijiensis this dorsal margin is 
very slightly concave. 
As in the males, the females of G. samoaensis differ 
from those of G. fijiensis on the forewings in having a 
less straight prominent, oblique, dark brown, post median 
line and narrower unicolorous median band enclosing the 
stigma. On the hindwings, the dark brown terminal band 
on G. samoaensis has a more irregular inner edge than G. 
fijiensis and also spikes clearly basally along vein 1A+2A. 
The additional brown scaling along the edge of the inner 
margin basally from the tornus is also far more evident in 
G. samoaensis. The creamy-yellow lateral stripe from the 
antenna to the posterior margin of the tegula above the 
hindwings in G. samoaensis is much whiter in G. fijiensis. 
Immediately behind this stripe is a small, distinct patch 
of long orange-brown hair scales in G. samoaensis-, these 
are creamy-yellow in G. fijiensis. The underside of the 
forewings and hindwings tend to be darker in G. samoaensis. 
The fore-tibae hair scales of G. samoaensis are cream with 
some dark scales; in G. fijiensis the cream is usually heavily 
suffused with pinkish-brown scales. 
Gnathothlibus samoaensis is readily distinguished from 
G. eras by the distinctive olive green colouring and more 
prominent markings, including the stigma, on the forewings 
of the male. The head, thorax, dorsal and lateral surfaces 
of the abdomen of the male are also olive green, these are 
brown in G. eras, as are the forewings. Even in specimens of 
G. samoaensis that show reduced overall green coloration, 
there is clear evidence of some degree of greenish scaling 
on the wings and body. Behind the thin lateral creamy- 
white stripe above the wings is a small distinctive patch of 
orange-brown hair scales on each side of the abdomen of G. 
samoaensis, these patches are creamy in G. eras. The dark 
brown terminal band on the hindwings of the males tends to 
be slightly wider in most specimens of G. samoaensis than 
seen on G. eras where it is often very narrow. Some brown 
scaling is also evident along the inner margin basally from 
the tornus in G. samoaensis. The dark brown terminal band 
stops at vein 1A+2A in G. eras. 
The long hair scales on the fore-tibae and fore-tarsi are 
slightly shorter on G. samoaensis than seen on G. eras. On 
the underside of the males of G. samoaensis the two dark, 
irregular, parallel, post median lines and the irregular sub¬ 
marginal line from apex to tornus on the forewings and the 
median and less obvious post median line on the hindwings 
are usually very evident to varying degrees. In G. eras usually 
only the dark submarginal line on the forewing is visible 
and often only to vein M 3 . The others are almost always 
vestigial or absent. 
The male genitalia of G. samoaensis (Fig. 16) differ from 
those of G. eras (Fig. 18) in having the uncus, in lateral view, 
longer, less distally enlarged, with a more rounded dorsal 
crest, a more concave apical margin and a smaller, pointed 
ventral tooth; in G. eras the dorsal crest is higher and more 
pointed and the apical margin is clearly straighter. Gnathos, 
in lateral view, slightly shorter and lacks the small upturned 
distal point seen in G. eras; in dorsal view, G. samoaensis 
has straighter sides and a blunt point, in G. eras the sides 
are clearly convex tapering to a sharper point. 
The specimens of G. samoaensis examined that showed 
less green appeared to be generally older which suggests that 
the green coloration may fade, to some degree, with age and 
exposure to light. 
Given that large numbers of only G. samoaensis 
were collected and sighted in November 2008 and other 
specimens in May 1985, it appears that G. eras does not 
occur on the Samoan islands despite being recorded from 
as far east as Tahiti. 
It should be noted that the closest populations of G. 
eras and G. fijiensis are to be found on the Fijian islands, 
some 800 km southwest of Samoa. When placed in series, 
or side by side as individual specimens, all three species 
can be readily separated by their external morphological 
characters alone. 
