32 
Psyche 
[March 
mon), Sapindus drummondii (scarce), Tillandsia usneoides (com- 
mon), and Ulmus crassifolia (common) have been found exclusively 
in the State Park. In addition to all plant associations described for 
the Botanical Garden, Bentsen Park supports distinctive gallery 
forest and water hole communities. Lush woods along the Rio 
Grande contain Salix nigra, Fraxinus berlandieriana, Celtis lind- 
heimeri, Mimosa belandieriana, Acacia farnesiana and a profli- 
gate ground cover of Serjania vines. Even more luxuriant is the 
flora near a permanent water hole, which includes huge examples 
of Fraxinus, Ulmus, Leucaena, and Ehretia, some Pithecellobium 
and Sapindus, numerous Xanthoxylum, some Mimosa, abundant 
Amyris, and an impressive epiphyton of Tillandsia usneoides on 
many larger trees. Other dark, damp zones in Bentsen Park are 
dominated by Pithecellobium flexicaule. 
Climatically and floristically, the Valley thus emerges as de- 
cidedly subtropical and the same is true for most of its fauna, 
from ichneumonid wasps and diurnal Lepidoptera to reptiles and 
birds. Indeed, south Texas harbors the richest Neotropic biota of 
any part of the United States. 
The Tribe Mesostenini 
Mesostenines are one of the largest groups in the Family Ichneu- 
monidae and inhabit all continents, having radiated massively in 
both tropical and temperate regions. They parasitize the pupae of 
many Lepidoptera as well as of some Coleoptera, Neuroptera, Dip- 
tera, and certain Hymenoptera. Most species are taxonomically 
catholic in host selection, each one being attracted to diverse kinds 
of pupae in a restricted spatial niche (leaf rolls, ground litter, stems, 
tunnels in tree trunks, etc.) rather than choosing victims from 
among one particular genus or even family of insects. 
Like most ichneumonids, mesostenines prefer humid forest habi- 
tats, so that in the New World they are best represented in the 
North American Temperate Deciduous Forest and again in various 
kinds of Latin American subtropical and tropical wet forests. The 
comparatively dry Lower Rio Grande Valley, thus has a rather de- 
pauperate mesostenine fauna, whose relations are principally but 
not exclusively Neotropic. 
Listed below together with relevant ecological, zoogeographic 
and taxonomic data are the 18 genera and 35 species of Mesostenini 
so far recorded from the Lower Rio Grande Valley. 
