352 Tachihidae. 



(Setigena). — 1907. Kat. palåarkt. Dipt. III, 316 (var. caesifrons). — 1921. 

 Baer, Zeitsohr. i angew. Ent. VII, 352. — 1924. Stein, Arch. f. Naturgesch. 

 90, 6, 110, 2 (Chaetogena). 



This species is very like the preceding, but is much smaller. 

 Head in shape and colour as in assimilis. Thorax and abdomen with 

 the pruinosity darker, and as a rule more bluish grey. Scutellum 

 quite dark, rarely a little reddish at apex; the apical bristles generally 

 very small to quite minute. Excavation on second abdominal seg- 

 ment not reaching hind margin, but leaving a relatively broad un- 

 excavated part. Fourth ventral sternite not drawn out in middle of 

 hind margin. Genitalia as in assimilis, but hypopygium not elongated, 

 about as long as broad, and upper forceps more narrowed towards base. 



Length 5,5 to nearly 10 mm, specimens of the larger size less 

 common. 



Ph. caesifrons is common in Denmark as elsewhere; at Copen- 

 hagen, Ordrup Mose, Ermelund, Dyrehaven, Geel Skov, Hillerød, 

 Grib Skov, Tisvilde, Boserup; on Langeland at Lohals; on Lolland 

 at Resle; in Jutland at Sønderborg, Sottrup, Høruphav, Madeskov 

 and Arnkiel ; the dates are ^^4 — V?- I have taken it in copula between 

 ^/g and 2^/5. It is a spring species especially common in May when it 

 is often present very numerously, and occurring in the low herbage 

 near the ground. Nielsen has (Vidensk. Medd. fra Dansk Naturh. 

 Foren. 67, 1916, 9) treated its biology; he bred it from various larvæ 

 of Geometrids occurring in spring on oak, birch and hawthorn, among 

 others Hibernia defoliaria; in each host only one parasite developed; 

 the host larva sometimes pupated with the parasite within, but most 

 commonly the parasite pupates outside; the pupa hibernates and 

 there is thus only one yearly brood. The species is also known from 

 the non Danish Arctia hehe. 



Geographical distribution: — Europe; towards the north to 

 middle Scandinavia, as it is no doubt mixed with assimilis by Fallen 

 and Zetterstedt, as proved with regard to the latter author, who 

 under assimilis mentions Danish specimens, and these are caesi- 

 frons. 



Remarks: The two species assimilis and caesifrons are, as seen, 

 rather similar; besides the differences in size and colour of scutel- 

 lum, one character, however, distinguishes them \\dth certainty 

 viz the excavation on second abdominal segment which reaches 

 hind margin in assimilis, but stops before it in caesifrons; Pandellé 

 has already remarked this, though he considered them as varieties, 



