Macrosaccus Davis and De Prins

Davis, Donald R. & De Prins, Jurate, 2011, Systematics and biology of the new genus Macrosaccus with descriptions of two new species (Lepidoptera, Gracillariidae), ZooKeys 98, pp. 29-82 : 32-36

Macrosaccus Davis and De Prins gen. n.

Type species:

Lithocolletis robiniella Clemens, 1859, by original designation.

Macrosaccus is assigned to the subfamily Lithocolletinae on the basis of the following putative morphological synapomorphies: hindwing vein Rs parallel to vein M and costal margin; adults rest with body parallel to surface; adult head with occipital tuft; and pupation occurring within the mine.

Diagnosis.

Superficially, Macrosaccus is similar to nearly all other genera of Lithocolletinae , sharing such characters as a well developed occipital tuft; a forewing pattern accentuated with oblique, whitish strigulae; and by the mode of pupation which occurs inside a silken cocoon within the whitish blotch mine usually on the underside of the host leaf without any prepared exit opening. However, in contrast to the typically solitary larvae and pupae of other Lithocolletinae genera, those of Macrosaccus are often gregarious inside a single, composite mine. The wing venation of Macrosaccus is similar to that of Cameraria and Phyllonorycter in possessing five apical veins, but it differs from the two latter genera in having Rs4 rising either from the base of Rs3 or stalked with Rs3. The hindwing venation is similar to Cameraria , Chrysaster , Leucanthiza , Neolithocolletis , and Phyllonorycter , but differs from Cremastobombycia , Hyloconis , Porphyrosela , and Protolithocolletis in the absence of vein M2. In the male genitalia, the sternum 8 is not produced caudally as in Chrysaster , Leucanthiza , and Protocolithocolletis . In Cameraria , Cremastobombycia , Hyloconis , Neolithocolletis , Phyllonorycter , and Porphyrosela , the sternum 8 forms a large flap underlying the valvae. The apex of the tegumen in Macrosaccus possesses a pair of tiny setae as in Cameraria , Chrysaster and Porphyrosela , but unlike Phyllonorycter which lacks apical setae. The transtilla of Macrosaccus is complete like that of other lithocolletine genera, but it differs from that of Cameraria and Hyloconis where it is incomplete. The female genitalia of Macrosaccus are characterized by numerous, microscopic spine-like signa which are scattered within the subcaudal part of corpus bursae (in other lithocolletine genera the corpus bursae bears other types of signa). Though the adult head of Macrosaccus is very similar to that of Protolithocolletis , the venation between these two genera differs with the forewing of Protolithocolletis more developed in possessing veins Rs1 and M2. The pupae provide perhaps the best characters for generic distinction, with that of Protolithocolletis lacking the spinose accessory cremaster ridge on sternum 7, which is characteristic for Macrosaccus .

Adult.

Head (Figs 10, 11). Vertex covered with long dense tuft of piliform scales; frons with smooth appressed scales; eyes of midsize; interocular index (= vertical eye diameter/interocular distance) ~ 0.75-0.96. Antenna about 0.7 × the length of forewing (n=9), smooth scaled, with a single row of scales per segment; scape with dense pecten. Proboscis well developed, naked, ca. 1.8 –2.5× length of labial palpus. Maxillary palpus very short, rudimentary, ~ 0.5 × length of labial palpomere II, and directed laterally; consisting of 2 articulated segments; basal 2 segments fused; segment 3 free, spherical. Labial palpus slender, drooping, with ratio of segments from base 1.5: 1: 2.

Thorax (Fig. 12). Forewing slender, maximum width/length ratio ca. 0.2, narrow at apex. Venation with 8 veins, apical part with 5 veins; Sc strong, extending nearly to costa, basal half of R indistinct, Rs2 present, Rs3 arises from apex of the cell, position of Rs4 variable, arising either from base of Rs3 or stalked with Rs3, M and CuA1 separate, CuP indistinct (fold) for entire length, 1A strong, separate, discal cell either open (with absence of crossvein between Rs2 and Rs3) or closed, extending ~ 0.78 of wing length. Hindwing lanceolate, maximum width 0.12 that of length, venation reduced, similar to Phyllonorycter ; Sc very short, Rs very long, extending almost to apex; basal 2/3 of M indistinct, parallel to Rs, distal part of M ends near distal 3/5: basal half of Cu strong, distal half indistinct, ending slightly before midway along dorsum; frenulum a single stout bristle in male, 2 tightly appressed bristles in female, retinaculum in male consisting of a broadly triangular curved fold from the ventral base of Sc and a few stiff, forward directed scales situated on the posterior part of Cu.

Abdomen. The margins of the abdominal opening strongly sclerotized and broad laterally, the sclerotized margination of abdomen opening unconnected on T2, S2 apodemes long, ~ half the length of S2, generally slender but more stout at basal 1/3 and very slender at distal 2/3; two pairs of tiny spinules on S2 sublaterally, and a pair of tiny spinules on S3-S6 sublaterally. Sternum 8 in male undeveloped.

Male genitalia. Tegumen relatively short, broad, moderately sclerotized laterally. Caudal portion covered with numerous tiny setae. A pair of long, slender setae present at apex of tegumen. Vinculum broad, U-shaped with very slender, elongate saccus which ranges from 1.1 –1.7× the length of valva. Valvae symmetrical, moderately broad, costal margin nearly straight to slightly curved; ventral margin variable between species from slightly convex to slightly concave over distal half with apex varying from fully round to abruptly narrowing; median surface of valva with sparse setae of medium length; apex of valva densely covered with longer, more stout setae. Transtilla complete and well developed, laterally expanded into rounded lobes. Aedeagus very long, nearly as long as entire genital capsule (from apex of tegumen to anterior end of saccus), straight and slender, of uniform diameter along its length; caudal end of vesica usually with long, slender cornuti; phallobase ~ ¼ total length of aedeagus.

Female genitalia. Papillae anales flattened, strongly interconnected, covered with short setae mostly along apical margin; basal bar broad but weakly sclerotized. Posterior apophyses slightly longer than width of papillae anales, straight and slender. Segment 8 short, weakly sclerotized. Anterior apophyses as long or slightly shorter than posterior apophyses, with moderately broad bases, then slender extending to caudal 1/3 of segment 7. Ostium bursae opens medially, near caudal margin of segment 7; sterigma simple, without cuticle folds, antrum funnel-shaped, narrowing anteriorly. Subcaudal area of segment 7 mottled with numerous tubercles. Ductus bursae ~ 2 × times longer than segment 7; a membranous accessory bursae ~ 2/3 the length of corpus bursae, arising from middle to anterior 1/3 of ductus bursae, with a smaller lateral pouch arising ~ midway along side of accessory bursae. Corpus bursae 1.0 –2.0× the length of segment 7, subcaudal region of corpus bursae usually with scattered spicules or with spicules arranged in linear rows in Macrosaccus robiniella .

Larva.

Hypermetamorphic with five larval instars. Earliest instars (1-3) highly modified sapfeeders with strongly depressed bodies and reduced chaetotaxy; 3 pairs of stemmata arranged in a lateral, anterior cluster on head; labrum short and broad, bilobed; anterior margin broadly concave, roughened, with minute dentations along inner margin of lateral lobes; maxillary and labial palpi absent. Later instars (4 and 5) tissue feeders, with cylindrical bodies. Head approximately round with full complement of mouthparts; 4 pairs of stemmata present; antenna 3-segmented with first segment moderately long; labrum strongly bilobed with raised median portion on each lobe; M1 absent; numerous secondary spines visible from inner, ventral perimeter of labrum. Thorax with SD1 elongate, immediately ventral to XD2; SD2 absent on T1, present on T2-3L group bisenose on T1-3. SV unisetose on T1-3. Legs relatively short but fully developed; coxae widely separated, with 4 coxal setae. Abdomen with D and SD groups bisetose on A1-8, 10; unisetose on A9; L group bisetose on A1-5, unisetose on A6-10; prolegs present on A3-5, 10; crochets of A3-5 arranged in a uniordinal circle; anal proleg with crochets arranged in a uniordinal semicircle opened caudally; anal plate with 4 pairs of setae.

Pupa.

Head with vertex terminating in a relatively short, broadly triangular, acute frontal process (cocoon cutter). Abdomen mostly covered dorsally and ventrally with dense, minute spines; dorsum of A2-7 with a single anterior row of short, stout spines; caudal half of sternum 7 with a transverse ridge (accessory cremaster) bearing ~ 18-21 mostly longitudinal rows of short, blunt spines; cremaster of A10 greatly reduced, nearly absent, consisting of 1-2 pairs of minute tergal spines.

Etymology.

The generic name is derived from the ancient Greek μακρο- (long) and σάκκος (bag) in reference to the elongate saccus in the male genitalia. Gender masculine.

Generic relationships and species diversity.

Several morphological specializations closely associate Macrosaccus with the genera Chrysaster , Cremastobombycia , and Phyllonorycter . Some of these involve the moderately produced proboscis (~ 2 × the length of the labial palpi) and the very reduced, two-segmented (with basal segment relatively enlarged), broad maxillary palpi (Figs 10, 11). The wing venation of all three genera is nearly identical and is among the most reduced within Gracillariidae . Only three branches of Rs are present in the forewing, accompanied by single branches of M and Cu (Fig. 12). Venation in the lanceolate hindwings is similarly reduced with only three major veins usually preserved (Rs, M, and Cu) in addition to the extremely basal Sc+R1. The position of Rs4 in Macrosaccus differs somewhat from that in the aforementioned three genera in arising either from the base of Rs3 or stalked with Rs3. Perhaps more significantly is that the discal cell is usually open in Macrosaccus due to the total or near absence of the Rs2-Rs3 crossvein. This crossvein is usually present in the other genera.

The most distinguishing feature in the male genitalia of Macrosaccus is the extremely long, rodlike saccus, whence the generic name is derived. The male saccus in Chrysaster , Cremastobombycia , and Phyllonorycter is either undeveloped or much shorter and stouter (except in two Afrotropical species Phyllonorycter farensis and Phyllonorycter obandai ). Likewise sternum 8 in all males of these three genera is extended caudally as a variably lengthened plate beneath the genitalia, compared to being unmodified in Macrosaccus . The female genitalia of Macrosaccus typically possess a relatively large, variably shaped accessory bursa arising approximately midway along the long, slender ductus bursae. The corpus bursae contains dense patches or faint rows of minute spines. The accessory bursae in Phyllonorycter originates more caudally near the ostium, and usually two, circular and variably sclerotized signa are present ( Davis and Deschka 2001).

The pupa of Macrosaccus is characterized by an accessory cremaster on abdominal sternum 7 that is unlike that of any other known gracillarid genus. This consists of a raised transverse ridge bearing ~ 18-21 mostly longitudinally oblique rows of short, blunt spines (Figs 84, 85). The accessory cremaster when present in Phyllonorycter differs greatly in consisting of a raised triangular area located midventrally on sternum 7 with 1-2 pairs of stout spines projecting laterally ( Davis and Deschka 2001).

In addition to the foregoing morphological characters, a preliminary molecular phylogeny based on ten genes also strongly places Macrosaccus apart from Phyllonorycter ( Kawahara 2010). Morphological characters distinguishing Macrosaccus from Phyllonorycter are summarized in Table 3.

Five species, all indigenous to the New World, are currently recognized in the new genus Macrosaccus . The high sequence divergence of the barcoding region of COI (> 7%) between species (Fig. 1, Table 2) further confirms the species concepts previously determined by morphological and larval host information. Sequence divergences within species for the 12 samples with multiple specimens were low and varied between 0-0.62% ( Macrosaccus gliricidius ), 0% ( Macrosaccus morrisella ), 0-0.46% ( Macrosaccus neomexicanus ), and 0-0.71% ( Macrosaccus robiniella ). The latter included specimens from Belgium and the United States.