Egg parasitoid wasps of the genus Polynema (Hymenoptera: Mymaridae) were collected over a 4-year period from crop-associated areas in southern Arizona. Seven morphologically distinct species were collected with 3 species identified. Evidence was found for the existence of an additional sibling species. Taxonomic characters currently used for this genus were evaluated for stability when the parasitoids develop in alternate hosts and some were found to be unreliable. A key to the Polynema species from Arizona were composed utilizing new characters. Biological studies were carried out on 5 of these species to determine host species, longevity, developmental time, and potential fecundity. Three of these species exhibit the potential for sympatric parasitization of the eggs of the threecornered alfalfa hopper. A 2-year study of the seasonal distribution of these parasitoids in alfalfa fields in southern Arizona was carried out.

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