Dryocosmus destefanii Cerasa & Melika, 2018

Cerasa, Giuliano, Verde, Gabriella Lo, Caleca, Virgilio, Massa, Bruno, Nicholls, James A. & Melika, George, 2020, Description of the sexual generation of Dryocosmus destefanii (Hymenoptera: Cynipidae: Cynipini) and disclosure of its life cycle, Zootaxa 4742 (2), pp. 359-374 : 363-370

Description of sexual generation of Dryocosmus destefanii Cerasa & Melika

Figs 1–6 , 8–26 , 28–35

Material examined. 3 females: Italy: Sicily, Cefalù (PA), loc. C.da Campella, ex galls on Quercus suber , 19.IV.2016, 38°1’19.06”N 13°59’15.49”E, 200m, ex pepper shaped gall, em[erged]. 20–21.IV.2016 (sample 6021), G. Cerasa leg. One specimen is deposited in the collection of Giuliano Cerasa, Giuliana, Palermo, Italy, one is deposited at the Museo Civico di Storia Naturale ‘Giacomo Doria’, Genoa, Italy, and the third in the collection of the Plant Health Diagnostic National Reference Laboratory, Budapest, Hungary (curator G. Melika).

2 males: Italy: Sicily, Cefalù (PA), loc. C. da Campella, ex galls on Quercus suber , 19.IV.2017, 38°1’19.06”N 13°59’15.49”E, 200m, ex gall shaped pepper, em. 20–21.IV.2017 (sample 6560), G. Cerasa leg. (one deposited in Museo Civico di Storia Naturale ‘Giacomo Doria’, Genoa, Italy; one at the Plant Health Diagnostic National Reference Laboratory, Budapest, Hungary); 1 male with the same label, but “(N. 6557) G. Cerasa leg.” (collection Giuliano Cerasa, Giuliana (Palermo) Italy).

Description. SEXUAL FEMALE. Head dark brown, except for brown lower face; mandibles light brown, maxillary palps and labial palps yellowish; antennae light brown, except amber scape, pedicel and F1–F2 amber to brown; eyes black.

Mesosoma light brown to brown, legs yellow-amber except for dark brown Ts5 and tarsal claws. Metasoma dark brown, T2 dorsally and laterally brown, subsequent tergites dark brown. Wings hyaline, veins yellow-brown to brown.

Body length 2.1–2.4 mm.

Head nearly 1.2 times as broad as high in anterior view ( Fig. 8 ), 2.3 times as broad as long in dorsal view ( Fig. 14 ); frons, vertex and interocellar area alutaceous, with rare white setae and small impression below median ocellus, eyes long with sparse minute setae mainly located on the outer margin ( Figs 8, 10 ).

Lower face alutaceous, covered by dense setae, with elevated median area and with striae radiating from clypeo-pleurostomal line, more diffuse medially on the face and reaching the ventral margin of the antennal toruli where they are stronger; malar sulcus absent. Clypeus small, smooth, rounded, slightly sinuous, ventral margin projecting over mandibles, marked by prominent epistomal sulcus, and with rare setae; anterior tentorial pits and clypeo-pleurostomal line distinct, shallow, ventrally emarginated. Gena alutaceous, not broadened behind eye in front view, covered in sparse setae. Occiput alutaceous to delicately coriaceous with few white setae; postgena alutaceous to delicately coriaceous, with rare white setae; area around occipital foramen impressed, devoid of setae. Postocciput around occipital foramen impressed; posterior tentorial pits distinct, elongate, deep; occipital foramen very slightly higher than height of postgenal bridge, which is nearly 1.9 times shorter than length of oral foramen; gula narrowed in lower half with very few and delicate longitudinal striae; gular sulci weakly impressed, touching one another in the lower half of gula and curved outwards in the upper half ( Fig. 9 ). Malar space short, 0.3 times as long as height of compound eye. Transfacial distance 1.0–1.1 times as long as height of eye and 1.4 times as long as height of lower face (distance between antennal rim and tip of clypeus); diameter of torulus slightly greater than the distance between them; distance between torulus and inner margin of eye nearly equal to the diameter of torulus. Ocelli elliptical in shape, elevated over dorsal margin of head; POL 1.3 times as long as OOL; OOL 3.0 times as long as diameter of lateral ocellus and 2.0 times as long as LOL. Inner margins of eyes parallel. Labial palpus 3–segmented, maxillar palpus 4–segmented. Antenna filiform ( Fig. 12 ), with 12 flagellomeres, nearly equal to body length, with short and sparse setae on all flagellomeres; pedicel as long as broad, pedicel and scape slightly (not more than 1.2–1.3 times) broader than F1–F12; scape + pedicel 1.2–1.3 times longer than F1, which is slightly longer than F2 or F3; F3 slightly longer than F4, which is 1.1–1.2 times longer than F5; F5 slightly longer than F6 or F7; subsequent flagellomeres F7– F11 gradually decreasing in length; F12 1.7–1.8 times longer than F11; placodeal sensilla present on all flagellomeres and arranged in one row, hardly detectable on F1.

Mesosoma very high, only 1.1–1.15 times as long as high. Pronotum glossy, with few long white setae along antero-lateral edge, rare in other parts; anterior rim of pronotum narrow, emarginate; transverse pronotal sulcus present, deep, areolate-rugose ( Figs 17–18 ); posterolateral pronotal area with some short rugae, longer and more pronounced in the posteroventral corner of pronotum ( Fig. 18 ); latero-median and median area of pronotum alutaceous without rugae. Propleuron alutaceous, smooth, glossy with sparse long setae, concave in mediocentral part ( Fig. 20 ). Mesoscutum smooth, glossy, with rare white setae along its lateral margin and rare adnotaular setae; slightly broader than long from above (width measured across base of tegulae); notauli complete, deeply impressed for full length; median mesoscutal line absent; antero-admedian line not impressed, faintly visible in antero-dorsal view of mesosoma ( Fig. 17 ), parapsidal lines absent; parascutal carina broad, anteriorly reaching notauli, mesoscutal suprahumeral sulcus not sculptured. Transscutal articulation deep, distinct. Dorsomedian area of mesoscutellar-axillar complex (disc of mesoscutellum+axillar foveae), nearly as long as broad from dorsal view, rounded, not elongated, marginated, smooth and glossy in the central part and with few wrinkles along margins only, with rare long white setae; raised and emarginated only along lateral edges, slightly overhanging metanotum.

Scutellar foveae subtriangular-ellipsoidal ( Fig. 13 ), distinctly delimited posteriorly and separated by narrow, weak central carina, deep with smooth and glossy bottom. Mesopleural triangle glossy with some delicate irregular short wrinkles and few white setae. Mesopleuron, smooth, glossy, with few delicate indistinct striae marking transepisternal line ( Figs 15, 16 ), anterodorsal part of mesopleuron and speculum smooth, glossy; essentially glabrous except very rare short white setae mostly concentrated close to the mesocoxal foramen. Pleurosternum smooth, glossy, with colliculate sculpture near mesocoxal foramina; acetabular carina delimiting a very narrow area laterally and with very delicate and short wrinkles adjacent to it ( Fig. 20 ). Metapleural sulcus reaching mesopleuron in the upper 1/3 of its height with some wrinkles; preaxilla smooth and glossy; dorsal axillar area alutaceous with a few delicate rugae and sparse setae, lateral axillar area smooth, glossy with short wrinkles and without setae; axillar carina broad, with longitudinal striae; axillula strongly sculptured in posterior end; subaxillular bar triangular, narrow, smooth and glossy, at posterior end shorter than height of metanotal trough. Metascutellum trapezoidal, smooth or very delicately sculptured, straight inferiorly, equal or slightly higher than height of ventral impressed rim of metanotum, which is smooth; metanotal trough smooth, glossy, without setae, with rare very weak wrinkles, without setae. Lateral propodeal carinae distinct and percurrent, strongly curved outwards in the middle ( Figs 19, 21 ), central propodeal area glabrous, smooth, glossy, without median propodeal vertical carina and with complexrugulose sculpture near lateral carinae; lateral propodeal area coriaceuos with irregular wrinkles and sparse white setae; nucha very short, with delicate longitudinal sulci dorsolaterally and laterally.

Forewing pubescent, hyaline, very weakly clouded around veins, 1.3–1.5 times as long as body, with distinct brown veins and long marginal cilia; radial cell open, 4.5 times as long as broad; R1 and Rs reaching wing margin and extending along it, Rs for more than half its length; 2 r slightly curved; areoles distinct, triangular and large; 2r-m not extending along M vein; Rs + M distinct, reaching basal vein in the lower half ( Fig. 22 ). Hindwing, pubescent, hyaline, very weakly clouded around veins with narrow infuscate stripe on the anterior margin, starting from hamuli and extending along the margin for more than 3/4 of its length ( Fig. 24 ).

All tarsal segments longer than broad, Ts1 the longest one; tarsal claws simple, without basal lobe; fore tarsomere I (Ts1) to V (Ts5) length ratio as 1.0:0.4:0.3:0.2:0.5; tibial spur long, curved inward, bifid at apex, nearly 0.4 times as long as basitarsus of foreleg ( Fig. 32 ).

Metasoma as long as mesosoma, about 0.8 times as long as length of head + mesosoma. Metasoma strongly compressed laterally, 0.8 times as long as high in lateral view, smooth, glossy, with rare and scattered white setae in T2 and T8 antero-laterally ( Fig. 23 ), present at moderate density on T9 forming moderate tuft; all metasomal tergites, except T2, with distinct uniform dense micropunctures; prominent part of ventral spine of hypopygium short, nearly 2.0–2.5 times longer than broad in ventral view, with long white setae, extending beyond apex of spine but never forming a tuft ( Figs 23, 25, 26 ).

MALE. Similar to female, but head and mesosoma completely dark brown; compound eyes bigger than in female ( Fig. 28 ); malar space extremely short, 0.11–0.12 times as long as height of eye, transfacial distance 0.7 times as long as height of eye and nearly equal to height of lower face; diameter of toruli 1.8 times as large as distance between them, distance between torulus and inner margin of eye about half the diameter of torulus. Ocelli bigger than in female ( Fig. 30 ); POL 2.4 times as long as OOL; OOL 0.7 times as long as diameter of lateral ocellus and nearly equal to LOL. Antenna slightly longer than body, with 13 flagellomeres, F1 distally broadened, excavated in basal half ( Fig. 11 ). Dorsomedian area of mesoscutellar-axillar complex (disc of mesoscutellum+axillar foveae) elongated, 1.3 longer than broad in dorsal view, trapezoid. Hindwing similar to female with narrow infuscate stripe on the anterior margin, starting from hamuli and extending along the margin for more than 3/4 of its length ( Fig. 29 ). Metasoma with long petiole, longer than wide ( Figs 31, 33 ).

Body length 2.3–2.5 mm.

Gall ( Figs 2, 4, 5 ). The gall is located on apical or lateral buds of young shoots. It is plurilocular, elongate and approximately shaped like a bell pepper fruit ( Fig. 2 ); the surface of young galls is green, smooth, glossy and sticky with apical white pale hairs and frequently has a reddish tinge. The color turns from green and plum to brown as the gall matures. Mature galls have a finely warty, non-sticky surface ( Fig. 5 ) and are approximately 6–8 mm in length and up to 5 mm in width. Inside the gall, the ovate and yellow larval chambers (2.3–2.7 mm) are surrounded with spongy tissue which later hardens and have their major axis arranged roughly parallel to the major axis of the gall ( Fig. 4 ).

Sexual generation galls of D. destefanii are similar to the galls of D. mayri but differ in having an elongate shape rather than being approximately spherical. In addition, D. mayri galls are monolocular, sometimes gregarious, individual galls are 5–7 mm in diameter, but often form irregularly shaped clusters 15–20 mm across.

Biology. Sexual generation gall development on Quercus suber begins late March and the first days of April, concomitant with the release of new leaves; the galls complete their development during the first half of April and the adults emerge during the last 10 days of the same month. As reported by Cerasa et al. (2018), the asexual generation galls begin development in May on the same host plant species, and adults emerge in August and the first half of September.

Diagnosis. Sexual D. destefanii most closely resemble D. mayri . In D. destefanii sexual females, the striae radiating from clypeus are more diffuse medially on the face and reach the ventral margin of the antennal toruli where they are stronger; LOL is nearly half of OOL, malar space is short, 0.26–0.27 times as long as the height of the eye; mesopleuron with few delicate indistinct striae marking transepisternal line; mesoscutellum rounded, not elongated, smooth and glossy in the central part; scutellar foveae subtriangular-ellipsoidal in shape; forewing 1.3–1.5 times as long as body, R1 and Rs reaching and extending along the wing margin (Rs for more than half its length); all metasomal tergites, except T2, with distinct uniform dense micropunctures. In contrast, in D. mayri sexual females the striae radiating from clypeus never reach the antennal toruli; LOL is slightly shorter than OOL; malar space very short, 0.16–0.17 times as long as height of the eye; mesopleuron without striae marking transepisternal line; mesoscutellum distinctly longer than broad, elongated, quadrangular or trapezoid, rugose to coriaceous in its central part; scutellar foveae rectangular; forewing longer than body, R1 nearly reaching wing margin, Rs extends slightly along margin; all metasomal tergites without micropunctures. In D. destefanii males the diameter of lateral ocellus is about equal to or slightly greater than OOL; POL 2.4 times as long as OOL; malar space very short, 0.11–0.12 times as long as height of eye; metasomal petiole longer than wide; all metasomal tergites, except 2nd, with distinct uniform dense micropunctures while in D. mayri males the diameter of lateral ocellus more than twice OOL; POL 2.8 times as long as OOL; malar space extremely short, 0.06–0.07 times as long as height of eye; metasomal petiole as long as broad; all metasomal tergites without micropunctures.

Distribution. Currently known only from Sicily, Italy ( Cerasa et al., 2018). The sexual generation decribed here was collected from the same locality as the asexual generation described in Cerasa et al. (2018).

Molecular results. A 433 base pair fragment of cytb was obtained for just the female sexual generation individual. This individual had a haplotype only one base pair different from that previously published for the asexual generation. A 544 base pair fragment of ITS2 was successfully sequenced from both sexual generation individuals and the one asexual generation individual. This gene was invariant among the three individuals. These very low levels of variation are typical of within-species variability in oak gallwasps (e.g. Nicholls et al. 2012, 2018a, Tang et al. 2016a, 2016b), and provide confirmation of the match between the sexual generation of D. destefanii described herein and the asexual generation of this species previously described by Cerasa et al. (2018). All new sequences are deposited in GenBank, accessions MN184638 – MN184641 .

Figures

FIGURES 1–7. 1–5, Dryocosmus destefanii sexual generation: 1, habitus, female (lateral view); 2, general appearance of gall; 3, habitus, male (lateral view); 4, dissected gall, showing the larval chamber; 5, magnification of the mature gall; 6–7, D. destefanii asexual generation galls.

FIGURES 8–16. Dryocosmus destefanii, sexual generation: 8, head, female (front view); 9, head, female (posterior view); 10, head, female (lateral view); 11, first antennal segments, male, the arrow shows the first flagellomere, excavated in basal half; 12, antenna, female; 13, mesosoma, female (dorsal view); 14, head, female (dorsal view); 15, mesosoma, female (lateral view); 16, mesosoma, female (latero-ventral view).

FIGURES 17–26. Dryocosmus destefanii, sexual generation, female: 17, pronotum, (anterodorsal view); 18, mesosoma (lateroventral view); 19, posterodorsal view of mesosoma; 20, mesosoma (ventral view); 21, metascutellum and propodeum, posterodorsal view; 22, forewing; 23, metasoma (lateral view); 24, hindwing, the arrows show the infuscation on the anterior margin; 25, ventral spine of hypopygium (lateral view); 26, ventral spine of hypopygium, ventral view.

FIGURES 27–35. 27, Dryocosmus mayri sexual generation, head, male (front view); 28–35, D. destefanii, sexual generation: 28, head, male (front view); 29, hindwing, male, the arrows show the infuscation on the anterior margin; 30, head, male (dorsal view); 31, metasoma, male (lateral view); 32, foreleg, female, the arrow shows the magnification of simple tarsal claws; 33, metasoma, male (ventral view); 34, mid tarsus and mid tibial spur, female; 35, hind tarsus and hind tibial spur, female.