Key to described species of Xanthomicrogaster (Modified from Penteado-Dias et al. 2002)

1. Mesosoma largely yellow (if dark spots are present, they are restricted to a single small sclerite).................................................. 2

- Mesosoma partly black; with distinct black markings on various sclerites, sometimes entirely black ............................................ 3

2. Mesosoma entirely yellow (sometimes with darkened apicolateral corners of propodeum); second metasomal tergum poorly sculptured, almost smooth; Brazil, Guyana, Suriname ...................................................................................... X. fortipes Cameron

- Mesosoma yellow with a distinct dark brown to black spot covering most of scutellum; second metasomal tergum rugose; Argen- tina ...................................................................................................................................................... X. otamendi Martínez sp. nov.

3. Mesosoma and hind coxa completely black; Brazil................................................................................................. X. pelides Nixon

- Mesosoma and hind coxa partly yellow ........................................................................................................................................... 4

4. Hind coxa blackish ventrally; second tergite blackened; Mexico............................................................................... X. seres Nixon

- Hind coxa yellow ventrally; second metasomal tergite completely yellow ......................................................................................5

5. Median lobe of mesoscutum partially black, metasoma black dorsally beyond tergite II; Brazil ...................................................... .......................................................................................................... X. maculatus Penteado-Dias, Shimabukuro & van Achterberg.

- Median lobe of mesoscutum and metasoma entirely yellow; Argentina .............................................. X. sayjuhu Martínez sp. nov.