Holotype, ♀, Inlet Beach, FL, collected July 15, 2015 by Scott P. Egan, AMNH ID#: AMNH_IZC 00238642

Allotype, same data as holotype

Paratypes, 2 ♂, same locality as holotype

Specimens from each collection locality (Table 1).

FEMALE. Length 1.6 – 2.3 mm. Holotype 2.3 mm

Color. Head, scrobal depression, pedicel, flagellum, mesoscutum, scutellum, coxae and metasoma metallic, olive green to turquoise to iridescent blue (colors depends on lighting and age of specimen); antennal scape white to yellow; femora and tibiae concolorous with mesoscutum but color lightens apically; tarsi white, except terminal segment dark brown (Fig. 1A, B).

Head. Head in fresh specimens as wide as mesosoma; in dorsal view 2.9 times as broad as long; eyes prominent and bare; vertex, frons, and clypeus reticulate; vertex and upper frons distributed with white bristles; scrobal depression extends from slightly below anterior ocellus to level of lower eye margin, smooth above torulus and striolate below; toruli located in lower third of scrobal depression; clypeus short, subquadrate, only slightly longer than wide; malus sulcus inconspicuous and 0.44 times eye length; mandibles with three teeth. Antennal scape 3.5 times as long as broad and 0.6 times eye length; Flagellum with nine segments, with anellus two-segmented, funicle four-segmented, and clava three-segmented. Funicular segments each with 2 rows of thick, mostly non-overlapping bristles (Fig. 2B). Relative length of scape, pedicel, anelli, funicle 1, 2, 3, and 4, and clava 1, 2, and 3 as 38, 12, 2, 24, 22, 22, 20, 16, 12, 8, respectively; two anelli with the same length but relative breadth of first anellus to second anellus as 6, 8.

Mesosoma. Pronotum, mesoscutum and scutellum reticulate; pronotum short in dorsal view, with six brown bristles at margin with mesoscutum; mesoscutum sparsely setose and setae inconspicuous; scutellum with many short setae and two pairs of strong setae in posterior third. Mesoscutum 0.95 as long as broad, mid-lobe convex, notauli complete and deep; axillae slightly advanced, their anterior tip extending to the approximate midpoint of the mesoscutum. Scutellum moderately convex and length 0.80 times length of mesoscutum. Propodeum 0.24 times length of scutellum and with strong median carina (Fig. 1B); callus with 6–7 bristles (Fig. 2A).

Wings. Forewing broad, extending past apex of gaster, marginal ciliae short; basal cell bare; submarginal vein with 6 dorsal bristles; postmarginal vein 1.3x length of stigmal vein; 3 admarginal hairs on left wing, four admarginal hairs on right wing; stigmal vein short and with large stigmus with 6 hairs on surface; 5 strongly-defined hair lines reaching dorsal and apical margin of forewing, with 3–4 additional less strongly defined hair lines that may or may not reach wing margin; 1 hair at median of radial cell (Fig. 2A). Hindwing 0.80 times length of forewing; hindwing moderately and evenly setose; hind marginal ciliae long.

Metasoma. Metasoma with petiole hidden in dorsal view; gaster elongate, 2.6 times as long as broad, and as long or longer than head and mesosoma combined; scattered white setae at posterior margins of each tergite becoming more dense towards the apex of the gaster; each cercus with two long bristles. Ovipositor extends slightly beyond apex of gaster (Fig. 1A).

MALE. Length 1.2 – 1.6 mm. Antennae inserted in middle of face (Fig. 2C). Funicular segments each with 3 loosely ordered rows of fine bristles. Gaster ovate; shorter than head and thorax combined. Other characters similar to female.

Named after the ancient Egyptian god Set, whose mythological stories mirror the natural biology of Euderus set. Set was the god of evil and chaos (Pinch 2004) and was reported to have control over evil animals like hyenas and serpents, just as Euderus set manipulates the behavior of its host, which is a parasite of trees (see Biology section below). The god Set is also reported to have trapped his brother Osiris in a crypt to kill him, later retrieving the body and chopping it up into small piece, which also fits with Euderus set, the crypt-keeper wasp, which kills its host in a crypt, and devours the host from the inside out, leaving major sections of exoskeleton (i.e., body parts) chopped up and distributed in the crypt (Weinersmith et al., in revision).

Two changes are required for the new species, Euderus set, to be included in the North American key to species of the genus Euderus by Yoshimoto (1971). First, a change is required to the key to subgenera of Euderus, where characters referring to the male flagellum should be removed. Yoshimoto (1971) used whorls of long hairs on the male flagellum as a diagnostic trait to discriminate between subgenera Neoeuderus and Euderus, but at that time only a single male specimen of subgenus Neoeuderus was available for study, and this individual was from the species Euderus viridilineatus for which no females had been found. As the male Euderus set. do not have antennae with pronounced whorls of long hairs, this is not an appropriate diagnostic trait for the subgenus.

We propose the following revision to the Yoshimoto (1971) key to subgenera:

Secondly, Yoshimoto’s (1971) key to the subgenus Neoeuderus should be revised as follows:

The two female Euderus set mtDNA-COI sequences were 98% identical to each another and each was most similar to other previously identified Euderus in the BOLD database. Sequence 1 was 88.4% identical to Euderus sp. D0703 on BOLD and sequence 2 was 89.8% identical to another Euderus sp. on BOLD (Ratnasingham and Hebert 2007). See Supplemental File 1 for the two specific mtDNA sequences.

Type locality for Euderus set is Inlet Beach, Florida, U.S. (Lat/Long: 30.273663, -86.001911), where it emerged from a stem crypt gall on Quercus geminata induced by the crypt gall wasp, Bassettia pallida. We have also collected Bassettia pallida galls from live oaks across the Gulf coast of the southeastern United States, where additional Euderus set have been found, including additional sites in Georgia, Florida, Mississippi, Louisiana, and Texas (see Table 1). Generally, we expect Euderus set to be restricted to the range of live oaks (Quercus; subsection Virentes; Cavender-Bares et al. 2015) upon which Bassettia pallida induce galls (Melika and Abrahamson 2007).

The genus Euderus Haliday is a small group of chalcidoid wasps belonging to the family Eulophidae (Burks 2003) where the majority are reported to be primary parasitoids of arthropods at all stages of development (Burks 1979, Burks 2003, Noyes 2016). Euderus set parasitizes the crypt gall wasp Bassettia pallida Ashmead, 1896, which forms galls on American live oaks in the genus Quercus and the subsection Virentes across the southeastern United States (Ashmead 1896, Melika and Abrahamson 2007, Egan et al. 2013). There are six to eight different cynipid gall wasps that are highly specialized and form galls on this same live oak complex (Egan et al. 2013). We have reared out many of the parasitoids from this large community, including clearly documenting the community from another gall former, Belonocnema treatae (Forbes et al. 2016), but this is the first time we have observed a member of the genus Euderus in this system after two decades of work (Lund et al. 1996, Egan and Ott 2007, Egan et al. 2012, Egan et al. 2013, Egan, unpubl. data).

Published records almost certainly underestimate the diversity of subgenus Neoeuderus in North America, and many other species in the subgenus may also be specialist parasitoids of oak galling cynipids. Yoshimoto (1971) noted that the biological records of the Nearctic Euderus indicate that most species are host specific, while also cautioning that host records for Euderus are patchy and the result of field observation, which only represent the most common species where there are substantial rearing records. While Yoshimoto noted just four members of subgenus Neoeuderus, the current work adds a fifth, and we have recently reared another from the honey comb leaf gall wasp, Callirhytis favosa, on pin oak in Iowa. While this undescribed Euderus parasitoid of Callirhytis favosa has not yet been extensively studied, it is most similar in appearance to Euderus set, Euderus crawfordi, and Euderus multilineatus. If this truly is a different species, then three of the six species in subgenus Neoeuderus are known parasitoids of the oak-associated Cynipidae.

Emergence of Euderus set in the lab from field-collected Bassettia pallida galls was concentrated from February to March coincident with new leaf growth of the host plants and adult maturation and emergence of the asexual generation Bassettia pallida (Melika and Abrahamoson 2007, Egan, unpubl. data). We also observed a smaller pulse in September and October, which could have been a natural occurrence, or induced by harvesting galled tissue and bringing it into a controlled environment. Regardless of harvest time (August or October), a similar emergence window was observed in February and March.

Euderus set is strongly associated with a behavioral phenotype in its host, the crypt gall wasp, Bassettia pallida, where infected gall wasps cut an emergence hole through the gall tissue as an adult, but then die and remain partially in the crypt to plug the emergence hole with its head (Weinersmith et al., in revision). When Euderus set emerges, it cuts an emergence hole directly through the head capsule plugging the hole (Weinersmith et al., in revision). The host’s behavioral phenotype may benefit Euderus set by making it easier for the adult stage to emerge from the crypt (as it now only has to emerge through the parasitoid’s head capsule, rather than through the tree stem itself; Weinersmith et al., in review). This putative behavioral manipulation of the host by its parasitoid Euderus set is the first time this has been described by the species-rich and economically important Chalcidoidea and is also the inspiration behind both the scientific name, Euderus set, and the common name, the crypt-keeper wasp.

In addition to Euderus set, we have also reared eleven additional natural enemy species from Bassettia pallida galls on live oaks (Quercus; subsection Virentes), including two inquilines (genera Synergus and Ceroptres) and nine parasitoids including three species from the genus Sycophila, two species from genus Ormyrus, one each from the genera Eurytoma, Acaenacis, and Brasema, as well as a parasitoid from the platygastrid subfamily Platygastrinae that we have not yet been able to key to genus. The natural enemy community requires further description.