A systematic review of the Nearctic parasitoid insect species in the subfamily Eulophinae is needed. Therefore, the author offers a taxonomic review of the North American species of two genera, Pnigalio Schrank and Sympiesis Förster. This will form a basis for subsequent revisions of additional genera and ultimately of the subfamily.
The revision redeﬁnes pertinent generic and species concepts bringing them into line with the concepts of modern taxonomy, provides keys and illustrations to facilitate identiﬁcation of the genera and species, gives adequate redescriptions of known species and descriptions of new species, provides distribution records and maps for each species, and records available information on larval habitats of hosts attacked by each parasitoid.
Some of the species treated are important biotic agents partially or wholly responsible for the homeostatic state of many agricultural and forest insect pests. The ecological data obtained so far bolsters the observations of Townes (1962) and Askew (1965), who suggest that parasitoid insects are more commonly niche-speciﬁc than host-speciﬁc. Niche is deﬁned here as a microhabitat, e.g. a mined leaf or needle, housing a microlepidopteran, coleopteran, dipteran, or hymenopteran larva. The parasitoid insect species treated here are truly niche-speciﬁc and often transfer from insect pests in microhabitats in crops of economic importance to insect hosts in similar niches in surrounding uncultivated vegetation, and vice versa.