Chondrometopum arcuatum Hendel, 1909

Schulten, D., 2021, The first find of the male Chondrometopum arcuatum (Diptera: Ulidiidae: Pterocallini), Ukrainska Entomofaunistyka (Oxford, England) 12 (2), pp. 29-30 : 29-30

Chondrometopum arcuatum Hendel, 1909 ( Figs 4–6)

Material. Peru: ACP Panguana , 9.62ºS, 74.93ºW, 20.09.2019, 1 ♂ (Schulten) (photo in the nature) .

Distribution. Guyana (Steyskal, 1968), Peru.

Remarks. All the species of Chondrometopum show strong sexual dimorphism in their wing venation and pattern ( Figs 2–3, 5–6, 9–10), with pterostigma enlarged and deepening posteriorly in males and only slightly modified in females (Kameneva, 2004). In addition, females of C. arcuatum and C. bifenestratum were known to have widened head ( Figs 4, 8), and male of C. bifenestratum having it even mote wide with horn-like genal processes ( Fig. 7), and C. leve was found to have heads of both male and female unmodified, as in many other Pterocallini ( Fig. 1).

The photograph of a picture-winged fly taken by DS in Peruvian Amasonia ( Fig. 5) was identified by EPK to as C. arcuatum . This is a male, which possesses genal “horns” similar to those in male C. bifenestratum , but clearly differing by the other characters given in the key below, including the abdominal tergites surface and vestiture.

The only key to species provided by Kameneva (2004) can be modified as follows:

A Key to Species of Chondrometopum (modified from Kameneva, 2004)

1 Head as wide as thorax or narrower, neither transverse, nor with genal processes. Thorax subshining brown.Acrostichal setae absent in both sexes. Wing venation and pattern as on Figs 2–3; its length <3.5 mm (2.0–3.0). ....................................................................................................... C. leve

— Head wider than thorax, in males with horn-like processes on genae ( Figs 4–5, 7–8). Thorax gray microtrichose. Acrostichal setae often present in females, absent in males. Wing length more than 3.5 mm (4.0–5.0). ......................................................................................................................... 2

2. Abdominal tergites shining black, rough, with smoothed papillae at bases of setulae. Wing: preapical crossband separated from basal dark pattern by complete hyaline area. Male wing pattern as on Fig. 5; female as on Fig. 6. ...................................................................................... C. arcuatum

— Abdominal tergites gray microtrichose, smooth, with shining black or brown spots at bases of setulae.Female:preapical crossband joined with basal dark pattern along vein R

2+3

. Male wing pattern as on Fig. 9; female as on Fig. 10. ......................................................................... C. bifenestratum