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American Midland Naturalist Monograph No. 3 



appressed scales, the hue of which is an important factor in separating the 

 species occurring in the United States. Although the prosternum has been very 

 little studied, Edwards (56) points out that the presence or absence of scales 

 or bristles on its upper part might be used to good advantage since they are 

 present in some mosquitoes and absent in others. 



Mesothorax (Fig. lOA, B). — The mesothorax comprises the largest por- 

 tion of the thorax, as in all Diptera, and bears many structures of prime 



postspiracular bristles 



spirocular brrsties 



posterior pronotol bristles 



anterior pronotol bristles 



upper mesepimerol bristles 



sternopieurol bristles 



PrK 



Fig. 10. Parts of thorax and pleural chaetotaxy of an adult Psorophora. (A) Pleural 

 chaetotaxy.(B) Lateral view with sclerites and positions of bristles indicated. AP, 

 anterior pronotum; AS, anterior spiracle; C^, first coxa; Cg, second coxa; Cg, third 

 coxa; HI, halter; M, meron; Mes, mesepimeron ; Mm, metameron; Mn, metanotum; 

 Mp, metapleura; Pn, postnotum; PP, posterior pronotum; Ppl, propleura; PrK, prealar 

 knob; PsA, postspiracular area; Pt, paratergite; S, scutum; SA, spiracular area; Sc, 

 scutellum; Sq. squama; SsA, subspiracular area; Stp, sternopleura ; WB, wing base. (C) 

 Dorsal view with positions of bristles indicated. Ac, acrostichal bristles; AP, anterior 

 pronotal lobe; DC, dorso-central bristles; PsS, prescutellar space; S, scutum; SA, 

 scutal angle; Sc, scutellum; SuA, supra-alar bristles. 



