Another enigma, or just another Gomphidia kruegeri?

17 and 18 August I spent happily navigating my way along the streams of Tay Thien in Tam Dao National Park when I noticed a large Gomphid perched along a rocky surface several meters above the stream. This cliff was very wet and dripping, the place deep in the forest. It looked like Gomphidia kruegeri, but the location was very different from the habitat I had encountered that species in in Ba Be. I managed to get a few shots of it, although not very good. The next day, I found another male, on the same stream, but several hundreds of meters removed. This time I could catch it for in hand examination. To my disappointment the appendages looked very much like those of G. kruegeri and as all other Gomphidia are rather different, I dismissed the possibility of it being something else. However, when checking carefully the photos I took at home, a creeping suspicion occurred to me. I had collected this last specimen, so decided to have another look, because on the photos the shape of the antrior lamina seemed different and the pattern on S3 was also quite different. It may well be that G. kruegeri is rather variable, but the differences I noticed do warrant more attention, especially as the individual I took pictures of the previous day displays the same characteristics. For comparison I include also photos of G. kruegeri. The reader can decide if this could be a variation, or something else.

The facial pattern of the Tam Dao specimen

The facial pattern of the Ba Be Gomphidia kruegeri

The first thing here that strikes us is the yellow spot on the labrum of G. kruegeri, which is missing in the specimen from Tam Dao. I have checked the photos published for G. kruegeri on the web for this feature and have only found photos displaying the yellow spot on the labrum. The yellow band on the anteclypeus and on the top of the frons are reduced (and on the frons also differently shaped), and also the yellow spots on the mandibles are greatly reduced. Is this just a very dark specimen?

Superior appendages Tam Dao specimen

Superior appendages of G. kruegeri

What is striking here, is the very straight appearance of the appendages compared to G. kruegeri, but there seems to be ample variation and the same could hold true of the pattern on S10. Intriguing is the length of the appendages in relation to S10 and S8. In the Tam Dao specimen this is (appendages - S10 - S8) 2:1:2.2. In the specimen from Ba Be this is 1.6:1:1.8, thus S10 is considerably larger. This is based on the photos of the complete insects in lateral view.

The Tam Dao specimen

The Ba Be G. kruegeri

What is striking is, apart from the more yellow coloration of G. kruegeri, which although the photos of the other Tam Dao specimen also shows that bleaker ground color, that G. kruegeri has a large yellow triangle at the ventral side of proximal margin of S3, and a dorsal spot, also at the proximal margin of S3. This is consistent in all photos of this species that I could check. Of course, although difficult to assess in this photo, the dorsal stripe is connected to the antehumeral spot to form a '7' , typical of G. kruegeri. The Tam Dao specimen on the other hand misses the basal ventral triangle on S3 and instead has a half ring on the dorsal half of the proximal margin, which is interrupted by the black dorsal carina. This is very interesting. A darker specimen might miss these very consistently present characteristics, okay, but it is not likely that it will then develop an almost opposite pattern.

The genital lobe of the Tam Dao specimen, note also the black ventral side of S3

The genital lobe of  G. kruegeri. 

The genital lobe of G. kruegeri has a characteristic hook at the tip and a round distal profile. There is some variation between the subspecies. The genital lobe of the Tam Dao specimen has a more triangular outline and the hook is absent.

The dorsal pattern of the thorax of the Tam Dao specimen

The dorsal stripe is not connected to the antehumeral spot, as is typically the case in G. kruegeri. In that respect it looks like G. perakensis (from which it differs in many other respects).

Not too sharp photo of another Tam Dao specimen

Another photo of the same specimen as in the previous photo

What can be seen is that the specifics of the collected specimen are also displayed by the specimen in the photograph, although it has seemingly a little larger spot on the mandibles. The labium is all black. Needless to say, there where no other G. kruegeri like specimens not displaying these characteristics about. It also displays the same lighter ground color, robust appendages, dark S3.