Sphex argentatissimus, Doerfel, Thorleif H. & Ohl, Michael, 2015

Doerfel, Thorleif H. & Ohl, Michael, 2015, A revision of the Australian digger wasps in the genus Sphex (Hymenoptera, Sphecidae), ZooKeys 521, pp. 1-104 : 42-44

Taxon classification Animalia Hymenoptera Sphecidae

Sphex argentatissimus sp. n.

Material examined.

Holotype. ♂, AUSTRALIA:NT: 27.5 km SE of Katherine, 14°34'0"S, 132°28'5"E, 08.04.2008, G. Williams & W. Pulawski (AMS). Paratypes. AUSTRALIA:NT: Buley Rockpools, Litchfield National Park, 2♀, 19.-22.04.2008, G. Williams & W. Pulawski (AMS); Litchfield National Park: Wangi Falls, 13°09.7'S, 130°40.9'E, 1♀, 22.04.2008, W. J. Pulawski & G. A. Williams (CAS); 29 km NW Mataranka, 14°45.5'S, 132°51.1'E, 2♂, 06.04.2008, W. J. Pulawski & G. A. Williams (CAS).

Diagnosis.

Females of Sphex argentatissimus are unique among the members of the Sphex subtruncatus group in combining the following characters: appressed pubescence on clypeus golden, wing membrane without yellow tinge, and pubescence on propodeal enclosure silvery-white. Males differ from those of the other species in possessing, additionally to the aforementioned features, a petiole that is considerably longer than flagellomere II and a conspicuous notch on the apical margin of metasomal sternum VIII. The former feature separates Sphex argentatissimus from Sphex ermineus , of which the petiole is shorter than flagellomere II, the latter one from Sphex cognatus and Sphex formosellus , in which the apical margin of metasomal sternum VIII is pointed.

Description.

Body black. Wing membrane hyaline, with fuscous band at apex. Wing veins dark brown to black. Appressed pubescence on clypeus and frons and erect setae on frons golden. Clypeus almost entirely covered with pubescence. Pubescence on collar and scutum brassy, except laterally and posteriorly on scutum, where it is denser and silvery-white. Scutellum convex. Propodeal enclosure covered with silvery-white pubescence, completely concealing sculpture.

Female: Body length 20.8-21.8 mm. Forebasitarsal rake with nine long spines. Free clypeal margin concave medially, with two lobes there, distance between which is less than 1/8 length of flagellomere II. Clypeus with erect golden setae. Distance between hind- ocelli 1.1 × their shortest distance to compound eyes. Scutellum without impressions. Length of petiole 1.6 × length of flagellomere II. Tomentum dense on metasomal tergum I and II.

Male: Body length 23.3-24.6 mm. Free clypeal margin truncate. Clypeus with few erect silvery-golden setae. Distance between hind- ocelli equal to their shortest distance to compound eyes. Posterior half of scutum with longitudinal median impression. Scutellum with medial impression near posterior margin. Length of petiole 1.4 × length of flagellomere II. Tomentum moderately dense on metasomal tergum I, sparse on tergum II. Metasomal terga V and VI with few bristles. Metasomal sternum VII with small fringe of silvery setae posterolaterally, sterna VI–I each with decreasing amount of setae. Apical margin of metasomal sternum VIII conspicuously notched so that two small lobes are formed, its lateral margin slightly concave posteriorly.

Discussion.

The males of this species have very reliable and distinctive features in which they differ from the other Australian Sphex . These features, however, are male sexual characters (free clypeal margin and metasomal sternum VIII) and thus do not help in establishing the sex association. Still, several characters indicate that both males and females belong to a single species.

In the Sphex subtruncatus group, there are only two species whose clypeal and propodeal pubescence resembles that of Sphex argentatissimus . One of them, Sphex pretiosus , is easily identifiable in possessing both silvery-white and golden pubescence on the propodeum. The females of the other one, Sphex cognatus , have golden, silvery-golden or silvery pubescence on the propodeal enclosure and are indeed very similar to those of Sphex argentatissimus . However, of the many examined females of Sphex cognatus , none had propodeal pubescence with the conspicuous white tone of silver that is characteristic of the males and females of Sphex argentatissimus .

Wing coloration is a similar case. Females of Sphex cognatus usually have a partially yellow tinged wing membrane, but sometimes it is almost entirely hyaline. On the other hand, the wings of Sphex argentatissimus have no hint of yellow at all.

Fig. 26B shows that the males and females of this species occur at least in the same overall region.

Etymology.

Argentatissimus is the superlative of the Latin adjective argentatus (silvery) and refers to the fact that the silvery color of the propodeal pubescence is much more intense in this one than in the similar species.