Taxonomic work Dutch Syrphid project

 

Recognition key literature

 

Chrysotoxum

Mark van Veen


Chrysoroxum parmense (Sack, 1932)

 

Introduction

Chrysotoxum are among my favourite hoverflies by their contrasting black and yellow pattern, long, black antennae and large size. They can be found at many places: near the ground flying through vegetation(e.g. C. arcuatum), on flowers (e.g. C. bicinctum), on leaves of scrubs and trees (e.g. C. cautum) and high up the trees (e.g. C. octomaculatum). Most species are found in association with open woodlands.

The precise feeding habits of Chrysotoxum are unknown (Rotheray, 1993). The larvae live in the ground, accociated with ant nests and are presumably predators of root aphids. There are reports of females oviposting about nests. The larvae of C. bicinctum was reared on pea aphids in the laboratory, supporting the predatory life history (Rotheray, 1993).

Recognition

Chrysotoxum consists of black and yellow hoverflies, with long antennae. They are broad bodied, in contrast to other black and yellow hoverflies with long antennae. They mimic social wasps and Speight (2000) remarks that C. fasciolatum is a surprinsingly good mimic of Vespula queens.

In the field, Chrysotoxum visually falls apart in two groups, depending on the amount of yellow on the abdomen:

  1. species that appear black with yellow stripes or bands (e.g. C. festivum, C. vernale, C. intermedium, C. elegans), and
  2. species that appear yellow with black markings (e.g. C. cautum, C. octomaculatum, C. arcuatum, C. fasciolatum).
This division is not taxonomically, but is based on field impression. Some species may be intermediate, e.g. C. arcuatum and C. elegans.

Two groups of Chrysotoxum cause difficulties because of their variability:

  1. Chrysotoxum intermedium and allies. I find considerable variability in C. cisalpinum, C. intermedium and C. lessonae. Specimens that would key out to C. cisalpinum contradict the description in Sack (1932), see the note in the key.
  2. Chrysotoxum elegans and allies. I find the species C. elegans, C. latilimbatum, C. octomaculatum and C. verralli difficult to separate because of the intraspecific variability. The Iberic C. latifasciata also belongs to this group. Typical specimens are not too difficult to separate, but atypical ones readily merge into one of the other species. It is doubted whether C. latilimbatum is a separated species (Speight, 2000).

Key

The key is essentially a translation of Van der Goot (1981) with additions from Sack (1932), Seguy (1961) and Speight (2000). The key was checked on C. arcuatum, C. cautum, C. elegans, C.fasciolatum, C. festivum, C. intermedium and C. vernale (my collection), C. caucasicum, C. cisalpinum, C. elegans, C. fasciolatum, C. lessonae, C. octomaculatum and C. verralli (collection ZMA, Amsterdam).
The nomenclatory changes of C. festivum and C. arcuatum are not followed. According to that nomenclature, the species known in Van der Goot (1981) as C. festivum L. becomes C. arcuatum L., while the former C. arcuatum L. becomes C. fasciatum Muller. The switch of the name C. arcuatum is highly confusing !

1.a. Antennae: 3rd segment long: as long as or longer than segment 1 and 2 together (fig. a, b)-> 2

1.b. Antennae: 3rd segment short: shorter than segment 1 and 2 together (fig. c) -> 8

Fig. a. Chrysotoxum arcuatum,
antenna.
Fig. b. Chrysotoxum cautum,
antenna.
Fig. c. Chrysotoxum festivum,
antenna.
 

2.a. Tergite 3 and 4 with short hairs, shorter than the height of basitars 1, seemingly bare -> 3

2.b. Abdominal tergites with long hairs, longer than the height of basitarsus 1 -> 5

 

3.a. Abdominal margin of tergites entirely yellow; antennae: segment 3 of equal length as segment 1+2 together [frons yellow] -> Chrysotoxum cisalpinum Rondani
Note: A marked character of specimens in the Zoological Museum Amsterdam (with abdominal margin entirely yellow and the antennal segment lengths as given above) is that they have a partly yellow frons in both male and female. This would make an easy characteristic against C. intermedium and C. lessonae. Seguy (1961) is cryptic about the male (antennal knob black), but describes for the female that there is a broad yellow band above the antennae. Sack (1932) describes the frons for both sexes as black. To complicate the matter further, some specimens in the ZMA are very close to typical C. cisalpinum, but their abdominal margin is black at the front of each tergite. They have a partly yellow frons. A study of type material is needed to check if both sexes of C. cisalpinum have a partly yellow frons and if the coloration of the abdomenal margin is more variable than assumed by Sack (1932) and Seguy (1961).

3.b. Frons black; abdominal margin black and yellow; antennae: segment 3 distinctly longer than segment 1+2 together -> 4

 

4.a. Tergite 2: spots form stripes that increase only little in width towards side margin -> Chrysotoxum intermedium Meigen
Jizz: blackish Chrysotoxum, yellow bands run from hind corner of side margin to front middle.

4.b. Tergite 2: spots triangular, increasing in width to cover almost the entire length of the side margin, margin itself black in front, yellow in hind part -> Chrysotoxum lessonae
Note: Addition of C. lessonae in this key is provisional. Sack (1932) is not very clear on this species and the above is also based on collection material of the ZMA.

 

5.a. Antennae: 3rd segment as long as segment 1 and 2 together (fig. a); abdomen relativily flat (use reference material); male: hypopygium relatively large, reaching over the hind margin of sternite 4; female: unique among European Chrysotoxum in possessing a longitudinal, median, membranous strip on abdominal tergite 6, which effectively divides this tergite into two parts -> Chrysotoxum cautum Harris
Jizz: Large, yellowish Chrysotoxum, often sunning or patroling on leaves. wing without dark spot. female: frons black. male: hypopigium reaches

5.b. Antennae: 3rd segment longer than segment 1 and 2 together (fig. b); abdomen strongly arcuate; male: hypopygium relativily small, at most reaching the hind border of sternite 4 -> 6

Fig. a. Chrysotoxum cautum,
antenna.
Fig. b. Chrysotoxum arcuatum,
antenna.
 

6.a. Thoracic dorsum shiny, except for the longitudinal stripes; femora yellow; male: frons yellow with a black spot above the antennae -> Chrysotoxum caucasicum Sack
jizz: wing without dark spot, abdomen black with broad yellow bands that are widely interrupted in the middle.

6.b. Thoracic dorsum with dark pollinosity, dull (and with longitudinal stripes); femora usually with black basis; male: frons black -> 7

 

7.a. Wing: front margin hyaline, except for the stigma, without dark spot in the top half; abdomen short and oval; smaller species: 2-12 mm. -> Chrysotoxum arcuatum Linneaus
Jizz: rather small, with equal coverage of black and yellow at first glance. Often foraging and flying close to the ground.

7.b. Wing: front margin yellowish with a distinct dark spot in the top half; abdomen elongate; large species: 13-17 mm. -> Chrysotoxum fasciolatum DeGeer

 

8.a. Abdomen with distinct yellow bands on tergite 2 and 4 only, the other tergites black (typical specimens), or with thin yellow bands (var. tricinctum) -> Chrysotoxum bicinctum Linneaus
Jizz: only two strong yellow bands with are mostly uninterrupted are typical. Somewhat similar to D. tricinctus, but that species has short antennae.

8.b. Abdominal tergites 2-5 with yellow, normally interrupted bands of equal strength -> 9

 

9.a. Abdominal margin black, the yellow bands do not reach it; wing: dark spot at the front in the tophalf -> 10

9.b. Abdominal margin yellow and black, the yellow bands reach it; wing with or without dark spot -> 12

 

10.a Antennae: 1st segment longer than the 2nd segment; femur 2 and 3: black on basal half; wing: dark spot large; scutellum: black with yellow hind border -> Chrysotoxum lineare Zetterstedt
Jizz: Abdomen extremely elongate, a dark species;

10.b. Antennae: 1st and 2nd segment of equal length; wing: femur 2 and 3: entirely yellow or black on basal quarter; dark spot small; scutellum: black with broad yellow margin or alomost entirely yellow -> 11

Chrysotoxum lineare (Sack, 1932).
 

11.a. Femur 1 and 2 completely yellow; katepisternum normally with yellow spot -> Chrysotoxum festivum Linneaus
Jizz: blackish Chrysotoxum with well defined yellow bands, in the field equal to C. vernale and similar to C. lineare and C.elegans.

11.b. Femur 1 and 2 yellow with black basis; katepisternum normally without yellow spot -> Chrysotoxum vernale Loew
Jizz: blackish Chrysotoxum with well defined yellow bands, in the field equal to C. festivum and similar to C. lineare and C.elegans.

 

12.a. Thoracic dorsum: longitudial stripes of light dust merged or separated by a black space much smaller than the width of a stripe, stripes reach from front almost to base of scutellum -> Chrysotoxum parmense Rondani
jizz: spots broad and lemon yellow, thoracic stripes large and long

12.b. Thoracic dorsum: longitudinal stripes of light dust separated by a back space equal to the width of a stripe, stripes reach from front to just over the middle of the dorsum -> 13

Chrysotoxum parmense (Sack, 1932).
 

13.a Tergites 3 and/or 4: black front margins interrupted at the side margin by a yellow stripe, the side margin itself black again (although somewhat variable, most specimens exhibit this feature on at leat one of the tergites); antennal knob in dorsal view: rectangular, protruding, undusted part elongate, about 1.25 to 1.5 as wide as long; female: hairs on side margins of thorax and abdomen, but especially on the postalar calli, very short -> Chrysotoxum octomaculatum Curtis
Jizz: Yellow Chrysotoxum, resembling C. verralli, but more rounded and therefore remniscent of a small C. cautum.

13.b. Tergites 3 and 4: black front margins not interrupted, front margin continously black; antennal knob in dorsal view: rectangular, protruding, undusted part broad, about 1.75 or more times as wide as long; female: hairs on side margins of thorax and abdomen, but especially on the postalar calli, halflong and fine -> 14

 

14.a. Tergite 2: the black front margin of equal width over much of its length because the front margin of the, interrupted, yellow band follows the tergite front margin closely and separates only at the side margin -> Chrysotoxum verralli Collin
Jizz: Yellow Chrysotoxum, closely resembling C. octomaculatum, but more elongate. Interrupted yellow band on tergite 2 appears as 2 triangular spots.

14.b. Tergite 2: the black front margin increases in width towards the side margin because the front margin of the yellow band does not follow the tergite front margin -> 15

 

15.a. Tergites 3 and 4: yellow hind margins small, smaller than the yellow band, or lacking -> Chrysotoxum elegans Loew
Jizz: More blackish Chrysotoxum, resembling C. festivum and C. vernalis. Interrupted yellow band on tergite 2 appears as interrupted stripes.

15.b. Tergites 3 and 4: yellow hind margins broad, as broad as the yellow band -> Chrysotoxum latilimbatum Collin
Note: colour variation of the former ?

 

Literature

Barendregt, A., 1991. Zweefvliegentabel, achtste druk. Jeugdbondsuitgeverij, Utrecht, 1-92.

Goot, V. S. van der, 1981. De zweefvliegen van Noordwest-Europa en Europees Rusland, in het bijzonder de Benelux. - Bibl. K. Ned. Natuurh. Veren. 32: 1-274.

Rotheray G.E. (1993) Colour guide to hoverfly larvae. Dipterist Digest 9. Whitely, Sheffield, UK.

Sack P. (1932) Syrphidae, In: Lindner E. Fliegen der Palaearktische Region, Teil 31. E. Nagele, Stuttgart.

Seguy, E. (1961) Dipteres Syrphides de l'Europe Occidentale. Memoires du Museum National d' histoire naturelle. Nouvelle Serie, Serie A, Zoologie, Tome XXIII. Paris.

Speight, M.C.D. (2000) Species accounts of European Syrphidae (Diptera): species of the Atlantic, Continental and Northern Regions. In: Speight, M.C.D., Castella, E., Obrdlik, P. and Ball, S. (eds.) Syrph the Net, the database of European Syrphidae , vol.20, 254 pp., Syrph the Net publications, Dublin

Torp, E., 1994. Danmarks Svirrefluer (Diptera: Syrphidae). Danmarks Dyreliv, Bind 6: 1-490. Apollo Books, Stenstrup.

Verlinden L., 1991. Zweefvliegen (Syrphidae). Fauna van België. Koninklijk Belgisch Instituut voor Natuurwetenschappen 39: 1-298, Brussel.

Updated 12.7.2001