Monobia, Montezumia and Pachymenes, Neotropical Elements in the Nearctic Fauna (Hymenoptera, Vespidae)

Abstract

The diplopterous wasp fauna of the Nearctic Region consists of three biogeographical elements.[1][1] (1) A few groups are apparently precinctive, showing no close affinities to wasps of other regions, at least in the living fauna: Euparagia, Pseudomasaris, Maricopodynerus, and Dolichodynerus. These form a very small percentage of the fauna (probably not more than 5%) and are almost restricted to the western United States. (2) The bulk of the species (probably over 80%) belong to Holarctic groups: Vespula, Eumenes, Odynerus s. str. (or Hoplomerus), Ancistrocerus, Symmorphus, Leptochilus, Rygchium and Pterochilus. In most cases the relationships to Palearctic species are unmistakable, the Nearctic forms differing sometimes in color only. (3) Finally some typical Neotropical groups have invaded the Nearctic Region, perhaps since the retreat of the Glaciers: Monobia, Montezumia, Pachymenes, Pachodynerus, Zethnsculus, Pseudodynerus, Mischocyttarus and Nectarina. The few Nearctic species of Polistes are also related to Neotropical forms, not to Palearctic species. In all the Neotropical element probably represents between 5 and 10% of the fauna. The distribution of Mischocyttarus and Nectarina was discussed in 1933 (Entomologica Americana, 13, pp. 87-150). That of Polistes and Pseudodynerus is considered in forthcoming papers. The present article deals with Monobia, Montezumia and Pachymenes. [1]: #fn-1