Chen Ng(Pg61-69)

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Shamshev & Grootaert: A review of the genus Stilpon from the Oriental region

Thorax dark brown. Scutum entirely tomentose. Postpronotal

bristle long, inclinate. Dorsocentrals in multiple rows,

complete posteriorly. Acrostichals 2-serial, complete

posteriorly.

Legs with colour pattern: hind femur brownish in apical 1/

2; fore tibia, fore and mid tarsi, mid femur at apex, mid and

hind coxae brownish yellow. Mid coxa with 2 brown bristles

on outer side. Hind trochanter lacking spinules. Mid femur

(Fig. 76) slender, with 3 short black antero- and 2 longer

posteroventral spines in basal 1/2, bearing 2 long yellow

bristles in extreme base. Hind femur (viewed laterally) more

or less evenly thickened, with row of anterodorsal bristles

becoming longer toward apex and row of prominent dorsal

bristles. Fore tibia lacking prominent ventral bristles. Mid

tibia with ordinary setation, lacking ventral spinules. Hind

tibia unmodified.

Wing normally developed, covered with uniform

microtrichia; more or less uniformly, rather deep infuscate.

Costal vein with long setulae along anterior margin. Vein

R2+3 about 2.5 times longer than Rs. Distance between apices

of R2+3 and R4+5 1.5 times longer than distance between

apices of R1 and R2+3. R4+5 and M parallel and straight in

apical part. Halter with elongate, contrast black knob and pale

stem.

Abdomen largely dirty yellow, bearing mostly scattered dark

setulae which are longer on pregenital segments, with all

tergites (except segment 8) of subequal in length, tergites 1-

2 unmodified. Hardly prominent gland-like structures present

between tergites 6-5, 5-4, 4-3 and 3-2. Segment 8 with

moderately long bristles.

Hypopygium (Fig. 77) brown, large. Hypandrium with 2 short

bristles in apical part. Epandrium completely divided. Left

epandrial lamella small, fused to hypandrium, with 2 short

bristles in apical part. Left surstylus with upper lobe (Fig.

78) largely divided; lower part with greatly developed

surstylar comb, upper part digitiform, fused with lower part

basally. Right surstylus (Fig. 79) moderately large, sublinear,

more or less rounded at apex, bearing numerous bristles of

different length, lacking spines. Left cercus unbranched, short,

fairly broad, rounded at apex, lacking spines and ventral

bristle, with 2 very long left marginal bristles in basal part.

Right cercus unbranched, short, rectangular, lacking spines.

Phallus short.

Female. Unknown.

Measurements. – Body length 2.5 mm, wing length 2.2 mm.

Etymology. – In reference to the largest size of this species

Figs. 80-84. Details of male abdomen, dorsal view. 80, Stilpon lek, new species, 81, Stilpon lekkwar, new species, 82, Stilpon trilobatus,

new species, 83, Stilpon malayensis, new species, 84, Stilpon paradoxus, new species; T – tergite. Scale bar: 0.1 mm.

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THE RAFFLES BULLETIN OF ZOOLOGY 2004

among all others found until now from the Oriental region,

“yai” means big in Thai.

Phylogenetic relationships. – The relationships of S. yai are

unresolved. The main problem originates because of unknown

female of this species. The presence of 2 long marginal bristles

in basal part of cercus may indicate S. yai is closer related

to some species of the S. divergens species group. However,

it has no a long ventral bristle on the left cercus, whereas the

presence of this bristle appears to support a monophyly of

this group. The structure of the phallus resembles that in the

S. graminum and S. seeluang species groups. However, this

character is insufficiently studied in many other Stilpon

species. S. yai has setose left cercus and 2 distinct bristles in

apical part of the left epandrial lamella. So, it cannot be

included in the S. graminum or S. seeluang species groups,

respectively.  S. yai shares the same condition of the left

surstylus as in S. paradoxus (upper part largely separated).

Additionally, in S. yai the right surstylus appears to be

enlarged and cerci might exhibit some tendency to be

completely fused (presumably, the conditions toward those

found in S. paradoxus). However, the last two arguments are

hypotheses only. Whereas the condition of the left surstylus

noted is a too weak argumentation to discuss some

relationships between these two species at present. Like some

North American species, S. yai has the elongate costal setulae.

But, again, this is probably a quite homoplastic character

because the lack of the scutal tomentum supports well the

monophyly of these Nearctic species.

Distribution and seasonal occurrence. – Thailand. Known

from one locality. The only record is from the beginning of

May. Collected from riverbed.

DISCUSSION

The phylogenetic relationships within Stilpon

The phylogenetic relationships within Stilpon are difficult to

resolve with the data currently available. The main problem

deals with the unclear sister relationships of the genus.

Nevertheless, Cumming & Cooper (1992) discussed the most

evident phylogenetic patterns within Stilpon. We tested the

implication of the newly described species on their

preliminary conclusions. The hypothesised phylogenetic

relationships of the species of Stilpon are presented in Fig.

85. The cladogram is a result of the heuristic search performed

using the programs NONA  (Goloboff, 1999) and, to submit

the data matrix, WINCLADA (Nixon, 1999). The data matrix

(Table 1) consisted of 23 morphological characters. We

should specially note here that the cladogram presented does

not pretend on a rigorous cladistic analysis. Such analysis is

impossible at present because the sister relationships of

Stilpon are unresolved. That was the reason why we did not

indicate the precise outgroup. To resolve this problem a

special study is needed that, however, is beyond of the scope

of this paper. Nevertheless, we considered that it would be

helpful for the future studies to visualise the possible

relationships within Stilpon. It is clear that this preliminary

analysis is mainly based on the characters which phylogenetic

value is more or less evident. In some cases they were checked

in other closely related taxa of the Drapetini.

The monophyly of Stilpon has been accepted here, following

Cumming & Cooper (1992), to be substantiated by two

apomorphies: linear to sublinear frons (character 1) and male

terminalia with a single ejaculatory apodeme (character 20).

Although, the first condition appears to present in some

closely related genera (Grootaert, 1994). Three informal

species groups of Stilpon have been previously recognised:

S. varipes group, S. graminum group, and S. divergens group

(Cumming & Cooper, 1992).

The lack of the scutal tomentum (character 4) and acrostichal

setulae (at least partial, character 6) was considered to support

the monophyly of the S. varipes species group. Our data

confirm this conclusion. All species treated in the present

paper share an entirely tomentose scutum and complete rows

of acrostichal setulae. The absence of the gland-like structures

on the male abdomen (character 9) could also indicate close

relationships of the species of this group. However, this

condition is present in some other species of Stilpon.

The monophyly of the S. graminum species group was

substantiated by the apomorphic development of apical spines

on the left cercus of the male terminalia. Within this clade

two monophyletic lineages have been recognised: S.

graminum, s. str., (upper lobe of the left surstylus completely

divided, female terminalia shortened, with the apex of sternite

8 hinged and at least partially separated from the base) and

S. nubilus (upper lobe of the left surstylus lacking comb,

sternite 10 of the female terminalia fused with anteroventral

margin of tergite 8).

The implication in the analysis of the newly described species

indicates that the S. graminum clade sensu Cumming &

Cooper (1992) is likely to belong to a broader branch of

Stilpon. This clade could be substantiated by the apomorphic

shortening of the female terminalia (character 21) and the

partial or complete division of the upper lobe of the left

surstylus of the male terminalia (character 12), assuming

subsequent reversal in S. nubilus Collin and its allies. The

clade appears to include two main lineages.

The first lineage agrees more or less with the concept of the

S. graminum group sensu Cumming & Cooper (1992)

(character 17). However, the relationships within the group

are not quite evident. S. spinicercus, the S. graminum and S.

nubilus complexes form one clade based on two characters

of the male terminalia, namely the presence of 2-3 apical

spines on the left cercus (character 17.2) and the prolonged

apically right surstylus (character 15). The S. graminum and

S. nubilus appear to be the sister complexes of the species.

This conclusion may be based on the shape of the female

cercus (character 22), which is broad oval in these species.

The absence of the abdominal gland-like structures could also

support this clade. However, this is a homoplastic condition

within Stilpon. The monophyly of the S. nubilus complex is

supported by the apomorphous presence of the apical spines

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