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1 June 2015 The Life History of Speranza exonerata Ferguson, 2008 (Geometridae: Ennominae: Macariini)
Michael W. Nelson
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Abstract

Speranza exonerata Ferguson, 2008 (Geometridae: Ennominae: Macariini) is a stenotopic moth only known from the northeastern USA. This species was reared from ova obtained from captive females in 2008 and 2009; the immature stages and life history are described. Both a larval host plant experiment and the discovery of wild larvae demonstrate that Speranza exonerata feeds on oak (Quercus L.), and does not feed on blueberry (Vaccinium L.). Larvae feed on scrub oak (Quercus ilicifolia Wangenh.), including both leaves and catkins, and Speranza exonerata may be a specialist on new growth of this plant. Ova are dormant through late summer, autumn, and winter, and hatch in early spring. Larval development is rapid (3–4 weeks), and corresponds to the availability of new growth of scrub oak. The pupal period is also brief (1–2 weeks), with adult moths flying in early summer.

The first valid description of what is now known as Speranza exonerata was authored by Douglas C. Ferguson, and published posthumously in 2008, in Fascicle 17.2 of the Moths of North America series. In the same work, Ferguson transferred about 50 North American species from the genus Itame Hübner, “1816” [1823] to Speranza Curtis, 1828. Prior to the publication of Ferguson (2008), the existence of an undescribed species in the genus Itame in the northeastern USA was known to lepidopterists for decades. Forbes (1948) incorrectly applied the name inceptaria to this species. It was more recently known as Itame “sp. 1,” or Itame “sp. 1 near inextricata,” due to its apparent close relationship to Speranza inextricata (Walker, 1861). Speranza inextricata is a species of the southeastern USA, occurring in Florida and Georgia (Schweitzer et al. 2011).

The known geographic range of Speranza exonerata extends along the Atlantic Coastal Plain from southern Maine south to New Jersey, and in the Appalachian Mountains from New York and Pennsylvania south to West Virginia and Virginia (Schweitzer et al. 2011). Within this range it is spottily distributed, and only found in pitch pine (Pinus rigida Mill.)-scrub oak (Quercus ilicifolia Wangenh.) barrens, both on sandy soils and on rocky summits and ridges. The population of Speranza exonerata that is the subject of this study occurs in and near Myles Standish State Forest, in the town of Plymouth, Plymouth County, Massachusetts, USA. The habitat at the collection locality (Fig. 1) is sandplain pitch pine-scrub oak barrens with small, scattered pitch pines interspersed with scrub oak, lowbush blueberry (Vaccinium angustifolium Aiton and V. pallidum Aiton), bearberry (Arctostaphylos uva-ursi (L.) Spreng.), and heather (Hudsonia L.).

Previously, the life history of Speranza exonerata was unpublished, but speculation as to its larval host plant focused on scrub oak and lowbush blueberry. These plants are common in pitch pine-scrub oak barrens, where Speranza exonerata occurs, and many barrens Lepidoptera feed on one or both of these hosts (Wagner et al. 2003). However, because most Speranza are host specific (Ferguson 2008), it seemed unlikely that both scrub oak and lowbush blueberry could serve as larval hosts.

The hypothesis that Speranza exonerata feeds on lowbush blueberry seemed plausible because two closely related species, Speranza brunneata (Thunberg, 1784) and Speranza sulphurea (Packard, 1873), feed primarily on species of Vaccinium (Ferguson 2008). Moreover, a third closely related species, Speranza amboflava (Ferguson, 1953), is known to feed on another ericaceous plant, Arctostaphylos uva-ursi (Ferguson 2008). However, in 1999, Timothy McCabe (New York State Museum) found a single final instar larva of Speranza exonerata on Quercus ilicifolia in the Albany Pine Bush (Albany County, New York, USA). That single larval collection was the basis for listing Quercus ilicifolia as the larval host of Speranza exonerata (then “Itame sp. 1 near inextricata”) in Wagner et al. (2003). Given no other evidence as to the larval host of Speranza exonerata, speculation that it feeds on lowbush blueberry persisted.

Methods

Host plant experiment. On 3 July 2008, in pine barrens habitat near Myles Standish State Forest (Fig. 1), in the town of Plymouth, Plymouth County, Massachusetts, USA, three female Speranza exonerata were taken live at a mercury vapor light and sheet setup. On 8 July 2008, four additional female Speranza exonerata were taken live at the same site with the same method. Each of the seven females was set up for oviposition in a separate plastic vial, each vial containing both a Quercus ilicifolia twig and a small strip of paper towel as opposition substrates. Each female was also offered a small piece of cotton saturated with a solution of honey dissolved in water. Viable eggs were obtained from six of the seven females. The eggs were kept through the remainder of the summer and the autumn on a shaded outside porch for a natural temperature and light regime, and through the winter in sealed vials in a refrigerator. The eggs were returned to the porch in early spring.

Fig. 1.

Pitch Pine-scrub oak barrens habitat of Speranza exonerata near Myles Standish State Forest, in the town of Plymouth, Plymouth County, Massachusetts, USA. Photographed 8 June 2009.

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In the spring of 2009, hatchling larvae from the six female Speranza exonerata obtained in 2008 were used in a larval host plant experiment, replicated six-fold. Eighteen hatchlings from each female were divided into three lots of six hatchlings, with each lot in a separate plastic vial. In each replicate, the first of the three lots was offered new growth (new leaves and catkins) of Quercus ilicifolia; the second lot was offered new growth (new leaves and flowers) of Vaccinium pallidum; and the third lot was offered new growth of both Quercus ilicifolia and Vaccinium pallidum. Rearing lots were kept on a shaded outside porch for a natural temperature and light regime. Every few days throughout the rearing process, each vial was cleaned of uneaten foliage and feculae, and fresh food of the same treatment offered (Quercus, Vaccinium, or Quercus plus Vaccinium). When larvae completed development, dry Sphagnum moss was added to the bottom of each vial as a pupation substrate.

Search for wild larvae. On 8 June 2009, foliage was beaten in the vicinity of where the female Speranza exonerata were taken the previous year (Fig. 1). A standard one meter square beating sheet was used to catch fallen insects. Beating was conducted for five hours while moving through the habitat.

Deposition of specimens. Both wild and reared adult moths were pinned and spread. Pupal shells were pinned. Ova, larvae, and pupae were preserved in 75% ethanol. Specimens were deposited at the Massachusetts Natural Heritage & Endangered Species Program Insect Collection and the University of Connecticut Insect Collection.

Results

Host plant experiment. In the larval host plant experiment, it quickly became apparent that Speranza exonerata feeds on Quercus, and does not feed on Vaccinium. In each of the six lots (from six separate females) that were fed Vaccinium, the six hatchling larvae wandered about the inside of the plastic vial, and over the Vaccinium foliage and flowers, but did not feed. Occasionally a hatchling appeared to be “tasting” the Vaccinium, but no feeding occurred. Within several days, all six hatchling larvae in each of the six lots that were fed Vaccinium were dead. The Vaccinium foliage and flowers were examined closely for feeding damage, but none was apparent, and there were no feculae in any of the vials.

In contrast, in each of the six lots (from six separate females) that were fed Quercus, the hatchling larvae began to feed immediately, on both the new leaves and catkins. The larvae grew rapidly, and most larvae completed development and pupated within three to four weeks after hatching. In each of the six lots (from six separate females) that were fed both Quercus and Vaccinium, the hatchling larvae began to feed immediately on both the new leaves and catkins of Quercus, but ignored the new leaves and flowers of Vaccinium. Every few days when the vials were cleaned and fresh foliage offered to the Quercus plus Vaccinium lots, the old Vaccinium foliage and flowers were closely examined, but no feeding damage was ever observed. As with the lots fed only Quercus, the larvae in the lots fed Quercus plus Vaccinium grew rapidly, feeding on the Quercus alone, and most larvae completed development and pupated within three to four weeks after hatching.

Search for wild larvae. The search for wild larvae of Speranza exonerata on 8 June 2009 yielded only a single third instar larva (which was collected and reared to the adult stage), despite beating of vegetation for five hours throughout the habitat where the adult females had been taken at mercury vapor light the previous year. Nevertheless, the larva was beaten from Quercus ilicifolia, and this observation, along with Timothy McCabe's 1999 collection in the Albany Pine Bush, provide evidence that Quercus ilicifolia is the larval host plant of Speranza exonerata in the wild. In addition, in the spring of 2011, David L. Wagner (University of Connecticut) found (and reared to adults) larvae of Speranza exonerata on Quercus ilicifolia growing in the Dwarf Pine Plains of eastern Long Island, New York, USA.

Figs. 2–7.

2. Speranza exonerata egg, 0.64 mm long x 0.43 mm wide x 0.32 mm high. Photographed 15 May 2009. 3. Speranza exonerata hatchling larva on catkin of Quercus ilicifolia. Larva 1.8 mm long, head capsule 0.23 mm wide. Photographed 21 May 2009. 4. Third instar larva of Speranza exonerata, ≈ 7.0 mm long, head capsule 0.64 mm wide. Photographed 29 May 2009. 5. Reared, early fifth instar larva of Speranza exonerata, ≈ 17 mm long, head capsule 1.6 mm wide. Photographed 6 June 2009. 6. Wild, late fifth instar larva of Speranza exonerata, ≈ 24 mm long, head capsule 1.6 mm wide. Photo courtesy of David L. Wagner, photographed 2 June 2011. 7. Speranza exonerata pupa, length ≈ 11 mm, width ≈ 3.6 mm at third abdominal segment. Photographed 27 June 2009.

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Description of immature stages. The following descriptions were written by examining living specimens and photos of living specimens, and later checked and expanded by examining preserved material. All specimens were from a population near Myles Standish State Forest, in the town of Plymouth, Plymouth County, Massachusetts, USA.

Figs. 8–9.

8. Speranza exonerata, adult male, reared in 2009. Wingspan 21 mm. 9. Speranza exonerata, adult female, reared in 2009. Wingspan 21 mm.

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Egg (Fig. 2). Oblong and flattened, 0.64 mm long, 0.43 mm wide, 0.32 mm high (N = 8). Color pale green when laid, within several days becoming pale yellow and then pinkish orange. Chorion sculptured with pits and ridges with tiny white knobs. Egg turns dark a day before hatching, as color of first instar larva begins to show through chorion.

First instar larva (Fig. 3). Length 1.8 mm at hatching (N = 8), growing to 2.9 mm (N = 4). Head capsule 0.23 mm wide (N = 8), rounded, smooth and unsculptured, orangish brown in color. Antenna white. Body very pale olive green (almost white), with broad, black stripe on dorsum from T1 to A9 and matching black stripe on venter. Prothoracic shield and anal plate indistinct, concolorous with body. Legs tan.

Second instar larva. Growing to 5.6 mm in length (N = 4). Head capsule 0.42 mm wide (N = 8), rounded, smooth and unsculptured, tan in color (lighter than first instar), with mottling on vertex. Clypeus and labrum tan; antenna white. Body pale olive green in color, with faint white mottling and indistinct, narrow and broken, white middorsal stripe along entire length of body. Prothoracic shield and anal plate indistinct, concolorous with body. Legs tan.

Third instar larva (Fig. 4). Growing to 9.2 mm in length (N = 4). Head capsule 0.64 mm wide (N = 7), rounded, smooth and unsculptured, tan in color with darker mottling. Clypeus tan with white ventral margin; labrum tan; antenna white. Body pale olive green in color, with white mottling. Indistinct, narrow and broken, white middorsal and subdorsal stripes along entire length of body. Prothoracic shield and anal plate indistinct, concolorous with body. Legs gray or grayish tan, becoming black proximally late in the instar.

Fourth instar larva. Growing to 14 mm in length (N = 4). Head capsule 1.1 mm wide (N = 7), rounded, smooth and unsculptured, orangish to pinkish tan (peach colored) with black mottling on vertex, lobes, and frons (mottling occasionally very dense, even solid black, on vertex, front of lobes, and frons). Clypeus white, or tan with white ventral margin; labium tan; antenna white. Body dark slate gray, with narrow and broken, white middorsal, addorsal, subdorsal, and lateral stripes along entire length of body. On Al to A5 (sometimes also A6), lateral stripe broadening around, or slightly anterior to, each spiracle into a white patch, with black patch or spot ventrad and slightly posterior to white patch; often with yellowish green patch in subspiracular area between segments. Spiracles tan. Venter mottled gray, with indistinct, narrow and broken, white midventral and adventral stripes. Prothoracic shield and anal plate indistinct, concolorous with body. Legs black proximally, orangish to pinkish tan (peach colored) distally.

Fifth instar larva (Figs. 5 and 6). Growing to 24 mm in length (N = 4), 2.4 mm wide at fourth abdominal segment (N = 8). Head capsule 1.6 mm wide (N = 8), rounded, smooth and unsculptured, orangish to pinkish tan (peach colored) with black mottling on vertex, lobes, and frons (mottling occasionally very dense, even solid black, on vertex, front of lobes, and frons). Clypeus white, or tan with white ventral margin; labrum tan with dark brown edge at notch; mandible tan with dark brown cutting edge. Mandible with seven teeth on cutting edge, plus one small inner tooth. Antennal base white, distal segments tan. Head setae tan to brown in color; no setae unusually short or long, longest setae two times the height of spiracle on T1; seta A3 displaced dorsally toward vertex, well above seta A2 and stemma 1, nearly as high as seta L1. Body dark slate gray to black with narrow and broken, white middorsal, addorsal, subdorsal, supraspiracular, and lateral stripes along entire length of body. On Al to A5 (sometimes also A6), lateral stripe broadening around, or slightly anterior to, each spiracle into a white patch, with black patch or spot ventrad and slightly posterior to white patch; often with yellowish green patch in subspiracular area between segments. Yellowish green patch of varying extent, occasionally covering most of subspiracular area and extending onto venter. Spiracles yellowish tan with black peritreme, those on Tl and A6–A8 larger than on A1–A5. Venter mottled, varying from brown to gray to black, with indistinct, narrow and broken, white midventral and adventral stripes. Prothoracic shield and anterior of anal plate indistinct, concolorous with body; posterior of anal plate, paraproct, and prolegs often tinged with pink. Legs black proximally, orangish to pinkish tan (peach colored) distally. Hypoproct and paraproct approximately equal in length, both one-third the length of anal plate. Crochets in biordinal homoideous mesoseries, in a single group with no medial lobe; 22–25 crochets on anterior proleg and 23–27 on anal proleg. Body setae tan to brown in color, occasionally more pigmented (dark brown or black); no setae unusually short or long, some on Tl longer than any on T2–T3 and some on A10 and prolegs longer than any on A1–A9, longest setae two and one-half times the height of spiracle on T1. On A1–A8, seta SD1 anterior to spiracle, seta L1 posterior, seta L2 anterior, and seta L3 posteroventrad, distances between SD1, L1, and L2 and spiracle each no more than half the distance between L3 and spiracle; A9 with setae D2, SD1, L1, and SV1 only, all four aligned from dorsum to subventer (none displaced anteriorly or posteriorly relative to others).

Pupa (Fig. 7). Length 11 mm, width 3.6 mm at third abdominal segment (N = 6). Fusiform; eye prominent; labrum hemispherical, length 0.72 of width (N = 6); labial palpus short, tonguelike, slightly longer than wide. Wing ending at posterior margin of fourth abdominal segment. Antenna and metathoracic leg equal in length, extending just beyond wing margin. Mesothoracic leg minutely shorter than antenna and metathoracic leg; proboscis slightly shorter than mesothoracic leg. Prothoracic leg ending in line with posterior margin of third abdominal segment. Prothoracic femur visible. Integument thin, yellowish to orangish brown on wings and other appendages; somewhat thicker and darker, orangish brown on head, thorax, and A1–A4; considerably thicker and darker brown on eyes and A5–A10. Integument smooth on wings, other appendages, head, and thorax. Mesothoracic spiracle raised and elongate. A1–A8 sculptured with numerous minute pits: anterolateral surface of A5 most densely pitted, with integument thickened and darker brown: A9 and A10 smooth except for rough sculpturing around base of cremaster. Head with one pair of setae near dorsal margin of labrum and two pairs at vertex: T1–T3 each with two pairs of setae: A1 with one pair of setae (anterodorsal): A2–A3 each with two pairs (posterodorsal and anterolateral): A4 with four pairs (posterodorsal anterolateral, posterolateral, and posteroventral): A5 with six pairs (posterodorsal, two anterolateral, posterolateral, anteroventral, and posteroventral): A6 with five pairs (posterodorsal, two anterolateral, posterolateral, and anteroventral): A7 with six pairs (posterodorsal, two anterolateral, posterolateral, anteroventral, and posteroventral): A8 with two pairs (anterolateral and posterolateral): A9–A10 with no setae. Cremaster with single pair of caudal spines.

Discussion

Larval phenotype. Larvae of Macariini may develop a darker phenotype when reared in crowded or humid conditions (Wagner et al. 2001). This may have been the case with the larvae reared for this study, as they developed a darker phenotype (Fig. 5) than the wild larvae collected by D.L. Wagner (Fig. 6).

Life history and behavior. The life history description presented below is inferred primarily from observations of captive individuals, and it should be noted that behavior in the wild may differ.

Adult Speranza exonerata fly in late June and early July. The adult moths are completely nocturnal (Ferguson 2008; Schweitzer et al. 2011). Female moths affix their eggs to twigs of scrub oak (Quercus ilicifolia). Eggs are pale green when laid, but within several days after oviposition they change to pale yellow, and then to pinkish orange (Fig. 2). Ova remain dormant through the remainder of the summer and the following autumn and winter.

The eggs hatch in mid- to late May, and the hatchling larvae (Fig. 3) begin to feed on both catkins and new leaves of the host plant. While early instar larvae will feed on either catkins or leaves, there appears to be a preference for catkins in the first and second instars, transitioning to leaves in the third instar (Fig. 4) and thereafter. When feeding on catkins, the larvae will consume both the flower tissue and pollen. When feeding on leaves, first and second instar larvae scrape tissue from one surface of a leaf, leaving the leaf skeletonized on one side. By the third instar, larvae chew through both leaf surfaces and finer vascular tissues, leaving small holes. Scrub oak catkins are largely gone by the time larvae reach the fourth and fifth instars, and so late instar larvae feed mainly on new spring leaves, chewing in from a leaf edge.

When not feeding, early instar larvae either remain in the catkins, where they are well hidden, or sit on the underside of a leaf, where they often align themselves with the midrib. Late instars rest either on the underside of a leaf (again, often aligned with the midrib), or on a petiole or twig, where they assume the straight and upright posture of a geometrid twig mimic.

Larvae grow rapidly, and by early to mid-June reach the fifth and final instar (Figs. 5 and 6). Once fully grown (≈ 24 mm long), larvae descend from the host plant, and pupate in the leaf litter without spinning any sort of cocoon (Fig. 7). The pupal period is brief, with adults emerging one to two weeks after pupation (Figs. 8 and 9).

Conservation status. While it is not known whether Speranza exonerata can feed on species of oak other than scrub oak (Quercus ilicifolia), the apparent strict association with habitats dominated by scrub oak suggest that Speranza exonerata may be a scrub oak specialist. Scrub oak barrens are a rare, and in many places disappearing, natural community (Wagner et al. 2003, Schweitzer et al. 2011). Association with specialized and threatened habitat, along with a relatively limited geographic range, as well as decline and apparent disappearance from some of its former localities, were all factored into the current conservation status rank for Speranza exonerata of G3G4, or “vulnerable to apparently secure” (NatureServe 2014).

Conclusions. The distribution of Speranza exonerata in the southern Appalachian Mountains has not been well documented, and surveys targeting scrub oak balds in that region are needed. To determine if oaks other than scrub oak (Quercus ilicifolia) are fed upon, host plant experiments offering different species of oaks could be performed. It is worth noting, however, that the known geographic range of Speranza exonerata corresponds remarkably well with the geographic range of Quercus ilicifolia, further suggesting that it may be a scrub oak specialist. Moreover, the early spring phenology of Speranza exonerata larvae suggests that this species may require catkins and new growth of leaves for successful development.

Acknowledgements

I would like to thank Timothy L. McCabe (New York State Museum) and David L. Wagner (University of Connecticut) for their encouragement and constructive comments and suggestions.

Literature Cited

1.

D. C. Ferguson 2008. Geometroidea, Geometridae (part): Ennominae (part): Abraxini, Cassymini, Macariini. Fascicle 17.2. 431 pp. In : R. W. Hodges (ed.). The Moths of North America. Allen Press, Lawrence, Kansas. Google Scholar

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W. T. M. Forbes 1948. Lepidoptera of New York and Neighboring States. Part II. Memoir 274, Cornell University Agricultural Experiment Station, Ithaca, New York. 263 pp. Google Scholar

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NatureServe. 2014. NatureServe Explorer: an online encyclopedia of life. Version 7.1. NatureServe, Arlington, Virginia,  http://explorer.natureserve.orgGoogle Scholar

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D. F. Schweitzer , M. C. Minno , & D. L. Wagner . 2011. Rare, Declining, and Poorly Known Butterflies and Moths (Lepidoptera) of Forests and Woodlands in the Eastern United States. Forest Service, U.S. Dept, of Agriculture, Washington, DC. 517 pp. Google Scholar

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D. L. Wagner , D. C. Ferguson , T. L. McCabe , & R. C. Reardon . 2001. Geometroid Caterpillars of Northeastern and Appalachian Forests. Forest Service, U.S. Dept, of Agriculture, Washington, DC. 239 pp. Google Scholar

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D. L. Wagner , M. W. Nelson , & D. F. Schweitzer . 2003. Shrubland Lepidoptera of southern New England and southeastern New York: ecology, conservation, and management. Forest Ecol. Manag. 185: 95–112. Google Scholar
Michael W. Nelson "The Life History of Speranza exonerata Ferguson, 2008 (Geometridae: Ennominae: Macariini)," The Journal of the Lepidopterists' Society 69(2), 77-82, (1 June 2015). https://doi.org/10.18473/lepi.69i2.a8
Received: 12 March 2013; Accepted: 16 October 2014; Published: 1 June 2015
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