Characterization. Depressaria depressana (Fabricius) (Depressariidae), known as Blunt's flat-body or purple carrot-seed moth, is native to the Palearctic region, occurring from Europe to China and the Russian Far East (Landry et al. 2013). The larva (Fig. 1) is brownish red with irregularly-shaped dull green regions laterally and ventrally, as well as dorsally along the intersegmental margins; the head, prothoracic shield, thoracic legs, and spiracular peritremes are black, and the setal pinacula are white. The adult (Fig. 2) is uniformly purplish brown dorsally, with the head and thorax, including the tegulae, white. In Europe, the larva of D. depressana is recorded to feed on the inflorescences of many apiaceous hostplants, including Daucus carota L., Pastinaca sativa L., Peucedanum oreoselinum (L.) Moench, and several species in the genera Carum L., Pimpinella L., and Seseli L. (Palm 1989; Landry et al. 2013). The moth is univoltine, spending most of the year in the adult stage.
Occurrence in North America. Landry et al. (2013) appropriately concluded that D. depressana is a recent introduction into North America, on the basis of the fact that it was not included in monographs on Nearctic “Oecophoridae” (including Depressariidae) by Clarke (1941) and Hodges (1974) (of Depressaria species, Hodges stated that only “cinereocostella, pastinacella, eleanorae, and alienella occur in eastern North America”). Landry et al. (2013) recorded D. depressana from the Canadian provinces of Ontario and Quebec, with the earliest date being 2008. In addition, J.-F. Landry (in litt.) reports: “I have reared adults from maturing larvae collected in the flower umbels of Daucus carota near Ottawa on 20 Sep 2014, with adults emerging from 25 Sep to 20 Oct 2014. Eleven voucher specimens in the CNC.” The moth also has been documented from the northeastern region of the USA. Photographs of the larva and adult of D. depressana from New York, Massachusetts, and Connecticut have been posted onto the BugGuide (2003–2015) web site, with the earliest date being 2010.
Very recently, it has become evident that D. depressana has expanded its range into the midwestern US. On 26 September 2014, James Vargo collected an adult D. depressana at UV light in Newton County in northern Indiana, and, on 2 August 2015, an adult D. depressana was photographed in Summit County in northern Ohio (photograph posted onto BugGuide). In July 2015, larvae and pupae of D. depressana were collected from inflorescences of Pastinaca sativa and Daucus carota in central Illinois, which at present represents the greatest southern and western range extension of the moth from its presumed point of introduction in southeastern Canada. A sample of two larvae on P. sativa was collected on 2 July 2015 near Urbana, along the entrance gate of Phillips Tract, a preserve owned by the University of Illinois at Urbana-Champaign. On 10 July 2015, an additional 21 individuals (11 larvae, 10 pupae) were collected on P. sativa and D. carota at Phillips Tract and also at a nearby overpass crossing Interstate Highway 74. In addition, on 13 July 2015, two D. depressana pupae were collected in a flower of D. carota, at a separate site approximately 5.5 km north of Urbana. Larvae and pupae were collected in situ on their hostplants and were reared to eclosion; adults were photographed and dissected, confirming their identity as D. depressana.
Similar species. Depressaria aliened a Busck, the adult of which is externally similar to that of D. depressana, is native to northeastern and far-western North America. The two species differ in a number of respects. Characters for differentiating adults of D. alienella and D. depressana on both external appearance and genital morphology were given by Landry et al. (2013). Furthermore, the host plants of D. alienella belong to the genera Artemisia L. and Achillea L. (Asteraceae) (Walsingham 1881; Clarke 1941). Also, Busck (1902) described the larva of Depressaria emeritella Stainton (a Palearctic species that in the adult stage closely resembles D. alienella, but now is believed not to occur in North America), as being “green with dorsal and subdorsal lines darker; head yellowish-green; first thoracic segment black dotted.” It is not clear, however, whether this was a second-hand description based on European accounts of the larva of D. emeritella (it closely matches, e.g., Stainton's (1861) description and figure of that species) or if Busck actually examined the larva of the native North American moth that he later described as D. alienella (Busck 1904).
Depressaria pastinacella (Duponchel), another Eurasian invasive species, can also be found on umbels of Pastinaca sativa in central Illinois in July, but it is unlikely to be mistaken for D. depressana. Morphologically, it can be distinguished by its pale body color and dark pinacula. It is also considerably larger in size: preserved final-instar larvae of D. pastinacella from Illinois average 19.5 mm in length (n = 5, range = 18.0–21.0 mm), versus 10.8 mm in D. depressana (n = 2, range = 10.0–11.5 mm). The two species differ phenologically and ecologically as well. In central Illinois, D. pastinacella larvae feed on flowers and immature fruits of wild parsnip primarily in June and larval development is largely complete by early July (Nitao and Berenbaum 1988). By contrast, D. depressana larvae are most abundant in July, when P. sativa inflorescences contain primarily immature seeds and D. carota inflorescences have not yet fully opened. Another difference is that multiple D. pastinacella larvae are not commonly found in a single umbel; the larvae are territorial and actively exclude potential usurpers (Green et al. 1998). By contrast, multiple individuals of D. depressana can be found occupying the same umbel (Palm, 1989; Fig. 3). Moreover, D. depressana pupates within the umbel (Fig. 4), whereas D. pastinacella burrows into the hollow stem of its host plant and spins a silken cocoon in which to pupate (Zangerl et al. 2002).
Parasitoid associations. No parasitoid records have been reported previously for D. depressana in North America. Two of the 11 D. depressana caterpillars collected during this study produced a single specimen of ichneumonid wasp. One of these ichneumonids is a phygadeuontine (Fig. 5). Phygadeuontinae is the largest subfamily of Ichneumonidae; species in this subfamily are typically idiobiont ectoparasitoids of holometabolous larvae, although life histories in this subfamily are diverse and include endoparasitoids and ectoparasitoids, koinobionts and idiobionts, hyperparasitoids, and some egg-sac parasitoids of chelicerates (Goulet & Huber 1993). The other larval parasitoid that we reared is a male Itoplectis conquisitor (Say) (Ichneumonidae: Pimplinae) (Fig. 6). I. conquisitor females typically oviposit in the mature larvae or prepupae of Lepidoptera from several families and are sometimes hyperparasitoids of other parasitoid wasps (Townes 1940). We do not know of any previous records of I. conquisitor attacking Depressariidae larvae; however, this species is highly polyphagous and widespread in North America (Townes 1940). I. conquisitor has been uncommonly reared from other Gelechioidea families, including Gelechiidae (Miller 1955; Pogue 1985; Loeffler 1994 (as a hyperparasitoid)) and Coleophoridae (Miller 1976). Other Itoplectis species, I. quadricingulatus (Provancher) and I. melanocephalus (Gravenhorst), attack several Depressaria species, including D. pastinacella and D. doncella (Denis & Schiffermüller) (Townes 1940; Gürbüz et al. 2009). In addition to the two ichneumonids that were reared from D. depressana larvae, a chalcidid of the genus Conura Spinola (Fig. 7) was reared from one of the 10 D. depressana pupae collected in this study. Conura species are typically parasites of the pupae of Lepidoptera, although some species attack Coleoptera or Hymenoptera, and some species are secondary parasites of braconid or ichneumonid-infested hosts (Bouček & Halstead 1997).
Ecological implications. In view of its status as more of an Apiaceae generalist than D. pastinacella, the possibility arises that in North America D. depressana may acquire native Apiaceae species as host plants. In fact, even the more specialized D. pastinacella has incorporated at least one North American apiaceous native species, Heracleum sphondylium subsp. montanum (Schleich. ex Gaudin) Briq. (reported in literature as H. maximum W. Bart ram and H. lanatum Michx.), into its diet (Berenbaum and Zangerl 1991). A cursory examination of a population of Zizia aurea Koch, flowering in the general proximity of infested D. carota and P. sativa populations (within a 3-km radius), failed to reveal any evidence of colonization of this native hostplant by D. depressana. Given the likelihood that this species is expanding its range throughout the eastern and central states, however, other native Apiaceae may be at risk of becoming incorporated into the hostplant range of this invasive species.
We thank Chris Grinter, for providing preserved larvae of D. pastinacella from the collection of the Illinois Natural History Survey, James Vargo, for the Indiana record of D. depressana, L. Field, D. Silsbee, J. Greenberg, and L. Armstrong, for posting photos of D. depressana from the USA onto BugGuide, and James Whitfield of the University of Illinois at Urbana-Champaign, for parasitoid identifications. This work was supported by National Science Foundation grant number NSFDEB1457731 to M.R.B.