Exyra semicrocea Guenee

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From unpublished notes

Distribution 1892-1921 (See Map)

Sarracenia flava

• North Carolina—Hamlet, Southern Pines
• South Carolina—Summerville
• Florida—DeFuniak Springs

S. sledgei

• Mississippi—Biloxi
• Alabama—Theodore, Mobile

S. psittacina

• Mississippi—Biloxi, Wiggins
• Alabama—Theodore

S. purpurea

• Alabama—Theodore, Delschamps

S. drummondi

• Alabama—Bay Minette, Theodore
• Florida—DeFuniak Springs

S. minor

• South Carolina—Summerville

S. rubra

• North Carolina—Southern Pines
• Dyar: Atlantic States
• Grote: Georgia, Texas
• Smith: Middle, central and southern states, New Jersey*
• Holland: New Jersey to Texas*

* New Jersey and Texas records may be misidentification errors, Xanthoptera semiflava in the case of Smith's records

Foodplants

E. semicrocea feeds on Sarracenia minor, S. rubra, S. sledgei, S. drummondii, and S. psittacina, habitually. When feeding on S. flava, it is usually replaced by E. ridingsii that may occur, and almost never is found in S. purpurea.

Description

Egg—High dome-shaped, less flattened basally than the egg of ridingsii; diameter, 0.58mm; height, 0.50mm; about 38 strongly cut vertical ribs or corrugations, but confluence becoming fewer toward the apex, and with the depressions between the corrugations faintly cross-ribbed; yellowish green, smooth, moderately polished, faintly punctate. Deposited singly usually on the inner walls of the pitchers of S. minor, S. rubra, S. sledgei, S. drummondii, and not infrequently in S. flava, though the insect does not seem to maintain itself very successfully in this plant; the egg-laying habit in S. psittacina was not ascertained, though where this plant occurs, it is an acceptable food plant.

Larva

Stage I—In color and structure almost identical with ridingsii but with the tubercles not quite as large; on segment T1, the smaller seta on the rho tubercle and the smaller seta on the kappa tubercle are almost obsolete; on segments A1, 2, 3, and 4, rho and kappa, of smaller size than in the total length at hatching, 2.6mm.

Stage II—As in the succeeding instars, purplish red tones usually prevail, rather than brown; width of head, 0.53mm; on segments A1, 2, 3, and 4, although the kappa tubercle is smaller than in ridingsii, the more marked and fleshy lateral expansion of the segment makes the "lappet" more conspicuous than in that species at this age; on T2 and T3, kappa is lower, smaller, and less conspicuous, than in ridingsii.

Stage III—Width of head, 0.87mm; the fleshy "lappets: of the first four abdominal segments are still further developed, perceptibly clothed with a sparse spinose pubescence, which continues, though much shorter, over these four segments, and less abundantly upon all the other segments.

Stage IV—Width of head, 1.1mm; this stage is marked by the definite appearance of the head pattern; by the full development of the abdominal "lappets," and their stronger setosity; by the more apparent short sharp pubescence of the general surface; by the comparatively small size of kappa on segments T1 and T2, and of the dorsal tubercles, alpha and beta, on segments A1, 2, 3, and 4, which latter, in ridingsii on these segments, are second only to the "lappet" tubercles in size, and far exceed the same tubercles on the other abdominal segments.

Stage V—Last larval instar; Sometimes brown, but usually bright vinous brown to clear wine red, strongly contrasting wit the intersegmentally white areas; the colored portions sparsely black pubescent, especially on segments A1, 2, 3, and 4, where longer denser pubescence, in some lights, forms a saddle shaped marking on each segment, surrounding and concealing the dorsal tubercles, alpha and beta.

Width of head, 1.6 to 1.7mm; color and head pattern quite similar to that of ridingsii, though the dark bands are usually narrower, the broad horizontal band across the face straighter on its lower edge, and the frontal suture less darkened with brown.

As in preceding instars, kappa on the thoracic segments alpha and bet on the first four abdominal, are much smaller than in ridingsii; the "lappets," (kappa, etc) on these four segments are large and fleshy, occupying a large portion of the width of the segments, and their bristly hairs are longer and more numerous than in ridingsii; as in that species, on A1, pi group is bisetose, from tubercles frequently not quite in contact, though in other examples they are partially fused; on A2, 3, and 4 trisetose, from tubercles more or less completely fused. Total length, before pupation, is about 28mm.

Pupa—Length, excluding caudal setae, 13mm. Pupal cuticle not heavily chitinized, thin, flexible; paler examples sufficiently transparent to exhibit the color pattern of the imago. Color varying from pale amber to dark chestnut brown. Front not strongly produced over the head. Prothorax of moderate length, epicranial suture present. Labial palpi indicated by a slit-like separation of the maxillae, narrowly in contact with the labrum. Mesothoracic wings extending to the incision between the fourth and fifth abdominal segments; metathoracic wings visible dorsally to the fourth segment. Maxillae and mesothoracic legs of about equal length, the maxillae slightly the longer, extending almost to the caudal margin of the wings, where a small portion of the metathoracic tarsi is visible. Antennae shorter, terminating about opposite the incision between the third and fourth abdominal segments. The mesothoracic legs do not reach cephalad to the eye-pieces; prothoracic tibiae narrowly visible. Dorsal cephalic margins of abdominal segments five and six striated; dorsal caudal margins of segments four and five punctate. Caudal end of body with two long straight setae and a few shorter slighter hooked setae; all the other setae fine, pale, very inconspicuous.

Imago

Male and female; expanse, 16 to 26mm; average expanse, 24mm; colors, black and yellow; a less robust species than ridingsii Riley.

Head—narrower than ridingsii; vestiture dense, hairy, brownish black; front with a pointed tubercular projection; antennae pale, finely scaled above, minutely ciliated below, in length about 6mm; tongue about 5mm long; palpi structurally similar to those of ridingsii, but slighter, usually dark above, tipped and fringed below with yellow, but varying from almost entirely light to almost all dark.

Thorax—convex, uncrested ; collar, anterior portion of patagiae , and thorax to center, rich velvety brownish black, the remainder clear yellow, rather brighter in tone than in ridingsii.

Legs—more slender than in ridingsii; tarsi and spurs pale; middle and hind legs pale dull brownish yellow, in the darker forms more or less mixed or clouded with gray; fore tibiae and femora brownish yellow with a greater admixture of gray, which sometimes darkens the tibiae to nearly black.

Wings—costa of primaries arched, apex rounded, outer margin regularly convex; the secondaries rounded, and about as wide as primaries; the markings are usually as follows: primaries to median line clear straw yellow, brighter than in ridingsii; the black median line slmost straight, crossing the wing at right angles to the costa; beyond this the wing is grayish black, the median line distinguishable by its deeper tone. This extremely simple pattern, by which the basal half of the wing is clear yellow, the outer half black or sooty, with a rigid line of demarcation between, is subject to great variation. The distance of the median line from the base is somewhat variable, though usually the light and dark areas are approximately equal; the inner edge of the line, usually clearly marked and distinct, rarely becomes diffuse, melting into the darkened yellow ground; beyond the broad straight median line, the wing sometimes becomes lighter, or even yellow, the transverse posterior line becoming visible on the lighter ground as a diffuse dark shade; or in extreme forms the median line may completely disappear, the whole primary becoming yellow, with only faint indications of any of the lines.

In the dark forms, the secondaries are smoky to black, unmarked, or sometimes paler at the base; in the extremely pale forms they are almost white, slightly shaded outwardly; sometimes they are pale, with a broad evenly-darkened border; the fringes vary from black to almost white.

Beneath, the dark forms are smoky, the basal third of primaries obscurely yellow; in the pale forms, the wings are pale dull yellow, outwardly more or less smoky.

Abdomen—slender, untufted, extending well beyond the secondaries, with which it is usually almost concolorous, ranging from almost white through dull yellow to almost black

Male genitalia much as in ridingsii, the valves shorter and blunter, the saccus shorter and proportionately broader.

From Pitcher Plant Insects II (Entomological News, Dec 1907)

"In the vicinity of Summerville, SC, the dry grass, weeds, and brush in the open pine woods and adjacent meadows where the pitcher plants grow, are burnt over each winter, with the idea of improving the pasturage for the cattle, which are allowed to graze in the unfenced woods and fields. This results in the destruction of a very large proportion of the hibernating larvae of Exyra ridingsii, and it is only in such spots as escape the annual burning that these caterpillars make their appearance in the spring. A full month before the appearance of the moths of this species, however, the moths of Exyra semicrocea Gn. suddenly appear in numbers in the leaves of the pitcher plants, both flava and minor. At this time (the middle of April), many of the flava leaves are well developed, but minor is much more backward and offers scant accommodation to the moths, which for about two weeks, are very abundant, sometimes as many as four occupying a leaf of flava. These moths evidently emerge from over-wintered pupae, as the flower buds and limited number of leaves available up to this time show no trace of larvae feeding; unlike ridingsii, they are even more abundant in the burnt over tracts than in those sections which have escaped the flames, for in the burned portion the new leaves which give shelter to the moths are more numerous. A peculiar habit of the larvae, it will be seen later, is probably responsible for their ability to survive the fires so destructive to ridingsii.

The moths of semicrocea and ridingsii are extremely averse to leaving their shelters; the leaves may be gathered and carried about almost indefinitely without disturbing them and at any attempt to dislodge them, they back further down the tube of the leaf and are almost sure to be badly battered and rubbed in the process. This instinct to walk backward when alarmed (they always sit heads up in the leaf), is so persistent that when removed from the leaf and placed upon a flat surface, they are more apt to walk backward than forward.

The spring brood of moths has practically disappeared by May 5th. The pale yellow eggs, placed singly and several inches down from the mouth of the pitcher, were frequently noted in the larger leaves of flava, but subsequent observations indicated that practically all of their eggs, or the newly hatched larvae from them, perished, and that the more suitable food plant of this species is minor, preferably the young and immature leaves not yet open at the top, though they also seemed to thrive, though less abundantly, in the tender unopened leaves of flava.

The young larvae have a very peculiar habit of feeding, which is evidently of great importance in insuring them safety from parasites and predaceous insects. They cut from one to three or even four encircling grooves around the inner surface of the leaf, well up in the swell of the hood, and extending as a tunnel out through the flat stiffening wing of the leaf. This groove is at first so small that it is invisible until the leaf is held to the light and its effect varies with the age of the leaf. In a tender unopened leaf, in which larvae are most frequently found, it quickly causes a shriveling and drying of that portion of the leaf above the groove, so that while the lower portion remains tender and juicy, entirely suitable for the young larva to feed upon, the upper part ceases to grow, and soon forma a hard dry cap to the leaf-tube, which is thus effectually closed to possible intruders. (See Plate XVI ), first figure, healthy leaf; second and third figures, leaves grooved by larvae.) On older leaves, however, the groove seems to have little effect, and in these, the larvae feed until large enough to undertake the ceiling of the open top with a web of silk. This web is usually spun from the angle of the lips of the pitcher in front, curving upward into the arch of the hood; but the habit is varied, and the web is occasionally spun directly across the tube at the highest possible point, just below the lips, like in ridingsii in flava; and in a few instances a double web, one from either side of the hood and meeting at the angle of the lips in front, was noted (see Plate XVI, three figures). The spinning of the web occupies only about thirty minutes. A single leaf usually carries the larva to the last or next to the last larval molt; on changing to a new leaf it spins the ceiling web in one of the three ways described, and sometimes also cuts an encircling groove which is usually obliterated by feeding before it has any effect on the leaf. Feeding from the top downward, the lower portion of the tube becomes filled with frass, on approaching which the larva reverses its position and feeds upward, sometimes even forcing its way down in the frass-filled tube, [so] that no available portion of the leaf may be left unconsumed.

A search for pupae in the leaves showing the effects of larval feeding was entirely unsuccessful, and very few were found in the large number of winter leaves examined.... When a leaf containing no larva, but showing evidence of continued feeding, was found, the cocoon could frequently be located in an adjacent leaf showing no trace of feeding; but isolated plants showing undoubted evidence of having furnished food to one or more larvae, often contained no cocoons in any of their leaves, indicating that the larvae, in their wanderings, must frequently fail to find suitable leaves, and presumably spin their cocoon in the moss and stubble which surround the growing plants. The instinct to desert the leaf in which it has fed, and to spin its cocoon where no trace of feeding will give a clue to its presence, no doubt in a measure [to] protect this insect from the enemy so fatal to the pupae of ridingsii, otherwise the abundance of semicrocea in tracts very thoroughly burned over, where no ridingsii larvae survive, can scarcely be understood.

The first pupae of the spring brood were noted May 19th , at which time many very young larvae were still in the leaves. The pupal period varied from fifteen to eighteen days, but may have been extended by removal to a colder climate. The earliest emergence was recorded June 1st , and the latest from this brood, not until July 11th , so that undoubtedly the later broods overlap more or less with those of ridingsii.

C. V. Riley has figured this insect in all its stages (Can. Ent . VII, 207 and elsewhere). His account of the larval habits is evidently based on observation of a later brood in mature leaves,: an the cocoon-spinning habit, as described by him, agrees more nearly with that of ridingsii than with semicrocea, as the two species were observed together at Summerville, SC.

Images

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• Exyra eggs and pupae
• Exyra Larvae
• Exyra pupae
• Exyra moths

Bibliography

• 1852. Guenee. Spec. Gen, Noct. II, 241 (Xanthop.)
• 1857. Walker. C B. Mus. Het., Xii, 818 (Xanthop.)
• 1896. Packard. Guide Study Ins, 316.
• 1873. Grote. Trans Am. Ent . Soc., IV 295
• 1874. Grote. Bull. Buff. Soc. Nat. Sci., II, 36.
• 1874. Riley. Can Ent. VI, 208, il . L.h .
• 1874. Riley. Trans. St. L. Acad. Sci., III, 236, il. L.h.
• 1874. Riley. Nature, X, 463.
• 1874. Riley. Am. Nat., VIII, 684
• 1875. Riley. Proc. Am. Assoc. Ad. Sci ., XXIII, 18.
• 1879. Grote. Can. Ent, XI, 236.
• 1891. Smith. List Lep. Bor. Am., 56.
• 1893. Smith. Cat. Lep. Sup. Noct ., 306.
• 1902 Dyar. List N. A. Lep., 211.
• 1903. Smith. Check List Lep. Bor. Am., 51.
• 1903. Holland. Moth Book, 248, il .
• 1904. Dyar. Proc. Ent. Soc. Wash., VI, 59.
• 1904. Jones. Ent. News, XV, 14-17. il.
• 1907. Jones. Ent. News, XVIII, 413-420. il.
• 1908. MacFarlane. Das Pflanzenreich, IV, 110, 17.
• 1909. Smith. Rpt. Ins. N.J., 472. (error in identity)
• 1917. Bar. & McD, Check List Lep. Bor. Am., 75.
• 1921. Jones, Natural History, 21: 296-316, 22 ill.
• 1942. Lloyd, The Carnivorous Plants, pgs. 36-37. 

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