The larva of Lacosoma arizonicum Dyar is figured for the first time. This species was previously known to feed on oaks (Quercus), but no specific Quercus species has been reported. We studied the life history of L. arizonicum and confirm four larval host plants from field-collected larvae: Quercus arizonica, Q. emoryi, Q. gambelii, and Q. hypoleucoides. Larvae were successfully reared to pupation in captivity on Q. virginiana (in Florida). A tachinid fly in the genus Lespesia, was reared from a single L. arizonicum larva.
There are approximately 300 described species of Mimallonidae (RAS unpublished) of which only four occur in America north of Mexico (Franclemont 1973). Species diversity is highest in the tropics; for instance, in the lowland Atlantic tropical rainforests of northeastern Costa Rica, as many as 19 species of mimallonids have been taken at a single station (DLW unpublished). In the western United States (not including southern Texas), two species are reported: Lacosoma arizonicum Dyar, 1898 and Cicinnus melsheimeri (Harris, 1841) (Franclemont 1973, Powell & Opler 2009). Since the original description of L. arizonicum and the works of Franclemont (1973) and Powell and Opler (2009), little has been published on the natural history of L. arizonicum. These authors mention oak (Quercus L.) (oak species unspecified) as the larval host. Powell and Opler (2009) record the flight season for L. arizonicum as June through August, with a late night to early morning adult activity period, approximately 2000-0400 h.
Below we report new observations pertaining to the life history of L. arizonicum. We figure the larva for the first time, document four Quercus species as hosts in nature, and provide the first record of a parasitoid reared from a wild-collected larva. We also provide new observations and discussion on the larval feeding behavior, pupation, and diapause in L. arizonicum.
Materials and Methods
Middle instar larvae of L. arizonicum were collected by RAS, LER, and AYK at two localities in southern Arizona, USA: Pima Co.: Santa Rita Mts., Coronado Nat. Forest, Box Canyon, 31.80075°, -110.76904°, 1490 m, 16.IX.2016, on Quercus arizonica Sarg. [one larva]; and Cochise Co.: Huachuca Mts., Coronado Nat. Forest, Sunnyside Canyon, 31.46495°, -110.38608° [coordinates approximate], ∼1985 m, 18.IX.2016, on Q. arizonica [one larva] and Q. emoryi Torr., Q. hypoleucoides Camus [six larvae total from latter two Quercus species]. The habitat at both sites where collections were made was Madrean evergreen woodland, dominated by evergreen Quercus species. DLW collected young larvae at two localities in southeastern Arizona: Pima Co.: Catalina Hwy, below Incinerator Ridge, 32.40956°, -110.70470°, 2360 m, 1.VIII.2012, on Q. gambelii Nutt. [one larva]; Cochise Co.: Carr Canyon Road, 31.42480°, -110.29922°, 2255 m, 24.VIII, 2016, on Q. hypoleucoides [three larvae].
RAS fed larvae on various Quercus sp. native to Florida, with only Q. virginiana being consumed for the duration of larval development. DLW reared his collections on natal hosts.
DLW's larval and photographic vouchers have been deposited in the Biological Collections facility at the University of Connecticut, Connecticut, USA. RAS's larval and adult vouchers are temporarily deposited in the research collection of Ryan St Laurent, Gainesville, FL, USA (CRAS), but will be donated to the collection of the McGuire Center for Lepidoptera and Biodiversity, Gainesville, FL, USA.
Natural host plants:We collected larvae on four oak species, Quercus arizonica, Q. emoryi, Q. gambelii, and Q. hypoleucoides in southern Arizona. Although our sample size is small, Q. hypoleucoides appears to be the favored oak species by ovipositing females.
Rearing: From eight larvae collected and reared by RAS on Q. virginiana, two individuals pupated. One of the two larvae sealed the anterior opening of the larval shelter prior to pupation in late X.2016, which eclosed as an adult male on 17.XI.2016 without diapause. This exceptional behavior, i.e., a November eclosion, may be a result of this individual being reared indoors with longer than normal photoperiods due to extended indoor lighting, and warm temperatures throughout the night (in Gainesville, Florida). In its natural habitat in mountainous southern Arizona, this species, being a lateseason feeder, is exposed to shorter photoperiods and colder nighttime temperatures.
The other larva, however, sealed both openings of the larval shelter and underwent diapause. It is worth noting that this individual was reared under the same conditions as the nondiapausing larva, suggesting variability in the indoor rearing setup or perhaps natural variation in diapausing behavior. Upon opening the overwintering larval shelter during February/March 2017, a larva was observed, not a pupa, confirming that L. arizonicum overwinters as a larva as in other North American Mimallonidae (Dyar 1900, Wagner 2005). The diapausing individual was kept outdoors in a small cylindrical mesh cage, roughly 30 cm tall by 15 cm in diameter.
Larval feeding behavior: Like all Mimallonidae for which the life history is known, L. arizonicum builds larval shelters which differ in structure depending on the age of the larva. Early instar larvae feed below a meshwork of silk and frass-netting that spans over the midrib of a leaf, or may be built along the edge of a leaf, curling the edge slightly (Figs 1, 2). Older larvae affix two or more leaves together with silk (Figs 3, 4), forming a shelter, which becomes more rigid and tubular in structure as the larvae develop and feed on the material surrounding the sealed compartment, often killing the incorporated leaves. The final shelter (case) is compact in structure, and has openings on either end, from which the larva extends outwards to feed, retracting inwards at the slightest disturbance. The entire inside surface of the larval shelter is generously lined with silk.
Larval description: Our observations of L. arizonicum larvae are based on 12 middle (Fig. 5) and late instar larvae (Figs 6–9, 11), as well as on photographs of the same individuals. We note morphological characters typical of the concealed-feeding Mimallonidae, specifically an enlarged, heavily sclerotized, rugose, anteroventrad projecting head and elongate prothorax; a thick abdomen with the widest segments being A4–A7; and a distinctly flattened, and heavily armored anal plate. There are two L group setae on T1. The crochet arrangement on the anal prolegs is unique: they form a transverse oval with the anterior crochets enlarged and distinctly biordinal (Stehr 1987).
The thick, pitted and verrucose head and flattened anal plate are apomorphic for mimallonoid larvae (Stehr 1987) and are clearly specialized (armored) for blocking the two openings of the larval shelter (Forbes 1923).
Coloration of the final instar is diagnostic, but with slight variation in the expression of yellow, as well as the degree of development of the broken longitudinal stripes (compare Figs 6 and 7). The thin middorsal stripe is usually continuous (especially anteriorad); there are three splotchy stripes, one subdorsal, and two supraspiracular. The yellow markings contrast with the dirty- to red-brown ground color. The thorax and abdomen are pale and mostly unmarked below the spiracles. The middorsal stripe divides the light redbrown prothoracic shield. The rugose head (Fig. 8) is handsomely patterned with silver-gray protuberances, giving way to black bars and lines above the level of the frons. The primary setae are white, peg-like, and somewhat widened apically. Middle and penultimate instars (Fig. 5) are similar to the final instar, but browner overall, with more subdued markings. Mature larvae are approximately 3–4 cm in length, but may stretch themselves to almost twice in length when extended from their shelters during feeding (Fig. 9).
We have not observed prepupal larvae directly because the larvae that survived to this stage remained within their larval shelters up until and during the pupal stage. However, Charles W. Melton provided photos (one shown in Fig. 10) of what we deduce to be a prepupal larva. This inference is based on the darker than usual coloration, wandering behavior as evident by the observed behavior of this individual being found crawling on the ground in an oak woodland, and the late season record: 5.X.2012 (C. Melton pers. comm.). The photo shows a larva similar to the one that we figure in Fig. 6, but more purple in coloration and fully fed. The purple hue is most obvious on the abdominal segments except A8–A10. Considering that this apparently prepupal larva was found in the absence of its larval shelter, we recognize the possibility that L. arizonicum may occasionally pupate outside of a shelter, but have not formally documented this behavior. Our specimen, however, did overwinter within the larval shelter.
Larvae of L. arizonicum are similar to those of L. chiridota Grote, 1864 (Dyar 1900, Wagner 2005) (Fig. 12), but markings of L. chiridota are less distinct due to reduced contrast between yellow dorsal markings and an overall yellowish tan coloration of the larval dorsum. We include images of both species for comparison (Figs 11, 12).
Parasitoid: Of the eight L. arizonicum larvae originally collected by RAS, five perished, two resulted in either an eclosed adult or a (presently, at time of writing) diapausing larva, and one penultimate instar produced a single tachinid parasitoid that pupated after the first week of October 2016. After the adult fly emerged from its puparium, it was killed and deposited in the Canadian National Collection of Insects, Arachnids and Nematodes, Ottawa, Ontario, Canada (CNC). James O'Hara (CNC) identified the tachinid specimen as a Lespesia species, possibly undescribed. This represents the first record of a parasitoid from L. arizonicum. The Janzen Costa Rican parasitoid database has records of Lespesia parasitizing Mimallonidae in the genera Druentica Strand, 1932 and Trogoptera Herrich-Schäffer,  (Janzen and Hallwachs 2017).
So far as is known, L. arizonicum is restricted to Quercus hosts, although it seems to be unspecialized with regard to oak species. Its eastern relative, L. chiridota, is also an oak specialist (Robinson et al. 2002, Wagner 2005). In the tropics, several woody families are used by Lacosoma, such as: Fabaceae, Lauraceae, Melastomataceae, Myrtaceae, Proteaceae, Rosaceae, Sapotaceae, Styracaceae, and Vochysiaceae (Robinson et al. 2010, Janzen & Hallwachs 2017). While it appears that many Lacosoma may be dietary specialists (Janzen & Hallwachs 2017, this paper), the alpha taxonomy of the genus is too nascent and knowledge of wild hostplant associations in the Neotropics are too incompletely known to assess to what degree diets might be more generalized.
Very little information is available regarding North American mimallonid parasitoids. Arnaud (1978) lists Chrysotachina alcedo (Loew) as a parasitoid of Cicinnus melsheimeri, which is interestingly a parasitoid of another concealed shelter former, the hesperiid Urbanus proteus (Linneaus). RAS has reared another inconclusively identified tachinid from C. melsheimeri sleeve-reared in Tompkins Co., New York, USA. Considering the paucity of parasitoid records for Mimallonidae, this is an area warranting further study. For example, it would be interesting to know if there are tachinid parasitoids specialized on unrelated concealed feeders such as Mimallonidae and Hesperiidae.
We thank Ana P. S. Carvalho, Charles Covell (University of Florida), and an anonymous reviewer for offering valuable corrections and suggestions. Richard Peigler (University of the Incarnate Word) provided RAS with the Arnaud reference, and pointed out the interesting similarity in host behavior of Chrysotachina alcedo. We offer a special thanks to James O'Hara (CNC) for his expertise in the identification of the parasitoid reared from Lacosoma arizonicum. Margarthe Brummermann gave us permission to use her photo of an adult L. arizonicum and Charles W. Melton provided excellent photos of a prepupal L. arizonicum larva, one of which is figured in this article. This study was funded in part by NSFDEB-NERC grant number 1557007 to AYK and by USFS Co-op Agreement 14-CA-11420004-138 and an award from the Richard P. Garmany Fund (Hartford Foundation) to DLW.