Distigmoptera borealis Blake, 1943

Konstantinov, Alexander S., Linzmeier, Adelita Maria, Coelho Morais, Ana Carla, Palmer, Michael W., Scheffer, Sonja J. & Lewis, Matthew L., 2019, Discovery of the First Nearctic Moss-Eating Flea Beetle, Distigmoptera borealis Blake, 1943 (Coleoptera: Chrysomelidae: Galerucinae: Alticini), The Coleopterists Bulletin 73 (3), pp. 599-610 : 601-609

Distigmoptera borealis Blake, 1943 ( Figs. 1–31, 35 )

Distigmoptera borealis Blake 1943: 217 (Holotype, male, type locality “ Swift Current , Saskatchewan,” USNM).

Description of Adult. Body 2.27–2.97 mm long, 1.24–1.45 mm wide, pubescent, elongate, moderately flat in lateral view. Dorsum from light yellowish/straw color to dark brown to blackish. Setae from white to yellow to black. Pronotum and head often darker; humeral callus lighter than rest of elytron. Elytron with 2 dark spots, 1 near middle adjacent to suture, within semicircular impression, another in apical third. Dark spots only visible when elytron light in color ( Figs. 2, 3 ).

Head ( Fig. 4 ) slightly convex in lateral view, evenly and strongly punctured and pubescent. Frons and vertex forming slightly convex line in lateral view. Supraorbital pore indistinguishable. Antennal callus visible, nearly quadrate; surface situated at same level as vertex. Midfrontal sulcus wide and deep. Supracallinal and supraorbital sulci absent, often substituted with punctures. Suprafrontal and supraantennal sulci shallow. Orbital sulcus absent. Orbit as wide as antennal callus. Interantennal space about as wide as transverse diameter of eye. Antennal socket rounded. Frontal ridge wide, parallel-sided. Anterofrontal ridge low, slanted dorsally, merged with frons. Eyes small, slightly protruding laterally; inner margin slightly curved. Labrum deeply notched in middle, with 6–8 setiferous pores, some placed symmetrically, others not. Antenna with 11 antennomeres; antennomere 7 widening abruptly compared to antennomere 6 ( Fig. 2 ).

Pronotum 1.43 times wider than long ( Fig. 5 ). Pronotal disc medially raised in 2 low ridges separated by shallow impression. Lateral sides of pronotum close to lateral margins, with 2 low and dull ridges. Anterior margin straight, with distinct border. Lateral margins subparallel, very slightly convex, without explanation. Lateral sides slightly convex in middle. Posterior margin nearly straight, without distinct border. Anterolateral callosity globular and evenly rounded, bearing seta, not forming denticle posteriorly ( Fig. 6 ). Posterolateral callosity small, bearing long seta. Pronotal surface covered with large, closely placed punctures and with yellow (posterior corners), whitish, and black setae. Scutellum triangular, roundish at apex, densely covered with whitish setae. Prosternal surface densely covered with irregular punctures. Prosternal intercoxal process extended posteriorly beyond coxa, truncate posteriorly; posterior end about twice as wide as middle. Procoxal cavities closed posteriorly.

Mesotergite with longitudinal mesothoracic ridge short ( Fig. 10 ). Mesanepisternum ( Fig. 12 ) as broad and long as mesepimeron. Mesosternum short. Mesocoxal cavity transversely ovoid. Mesoventral process concave at apex, longer than metaventral process ( Fig. 12 ). Metathoracic discrimen short. Metanotum with ridge D gently curved inwards and ridges C3 and D merging gradually ( Fig. 11 ). Ridge C3 about as long as C1, about twice length of C2. Oblique suture of metascutum poorly visible. Metascutellar groove nearly parallel-sided. Metendosternite ( Fig. 13 ) with thin stalk and arms about three times as wide as stalk at apex.

Elytral surface punctate ( Fig. 9 ), with punctures forming 9 striae (not counting marginal and short scutellar striae), densely pilose with black, yellow, and white setae. Interspaces generally flat. Humeral callus present. Base of elytron with callus situated between suture and humeral corner. Elytron with shallow pits slightly above middle along punctural rows 2 and 4. Epipleura nearly vertical, parallelsided until narrowing abruptly near elytral apex, not reaching apex. Elytral apex gently curved, acute.

Pro- and mesofemora slightly dilated. Pro- and mesotibiae subcylindrical, somewhat enlarged below middle, narrowing towards apical edge ( Figs. 2, 3 , 14 ), lacking apical spurs; long, curved setae present in addition to short setae. Metafemur greatly enlarged ( Fig. 15 ). Metatibia slightly curved in lateral and dorsal views. Outer and inner dorsal ridges more or less straight, with lateral ridge sharper than median. Transverse ridge forming denticle, connecting dorsal ridges near tarsal insertion. Metatibial apex with sharp denticle laterally adjacent to metatibial spur. Metatibial spur welldeveloped. First metatarsomere inserted preapically, about as long as subsequent tarsomere. Claw tarsomere swollen ( Fig. 15 ). Claw appendiculate in female.

Abdomen pubescent, with 5 visible sternites. Apical sternite shorter than 3 preceding sternites combined, without appendages basally ( Fig. 8 ). Basal sternite shorter than 3 following sternites together. Last abdominal tergite of female without groove in middle, evenly covered with long setae ( Fig. 7 ).

Median lobe of aedeagus simple, slightly curved in lateral view, with lateral margins almost parallel in ventral view; apex subtriangular, without denticle ( Fig. 16 ). Ventral side flatter apically than basally.

In female genitalia, posterior part of sternite VIII sclerotized along entire margin ( Fig. 18 ). Tignum with rounded anterior margin, evenly sclerotized, bearing many moderately long setae ( Fig. 18 ). Vaginal palpi elongate ( Fig. 19 ), strongly sclerotized anteriorly and along middle, merged anteriorly for more than half their length, each with about 8 apical setae, with posterior sclerotization about as long as anterior sclerotization. Spermatheca curved ( Fig. 17 ), with receptacle and pump not differentiated from each other (pump about as wide as receptacle). Apex of pump with flattened projection. Spermathecal duct as wide as receptacle at base, long, forming “S” coils.

Variation. The color of beetles varies greatly among specimens preserved as long ago as 1882 and those collected most recently. The older specimens are pale to almost straw-colored with uniformly light setae and the head, pronotum and often legs being a bit darker ( Fig. 1 ). The newly collected specimens ( Figs. 2, 3 ) have a darker (almost black) body surface, and the setae are white to dark yellow to black. This variability may also be a result of different preservation techniques, as well as geographic variation.

Diagnosis of Larva. Head well-sclerotized, slightly inserted in pronotum; body covered with several sclerites, arranged in two transverse rows on mes- and metathoraces and abdomen fused in single dorsal sclerite on pronotum.Integument with granulate microsculpture (grains ovoid) between sclerites. Hollowed, spatulate setae on dorsal sclerites; filiform setae on venter. Frons with pair of short digitiform setae close to endocarina. Stemmata absent. Antennae short. Presence of circular hollow on abdominal segments I–VII among dorsolateral sclerites. Legs slightly sclerotized; prothoracic legs smaller than following legs; pulvillus bladder-like.

Description of Larva. ( Figs. 20–30 ). Larva eruciform ( Fig. 35 ), slightly curved when preserved in ethanol. Head and pronotum somewhat narrower than following segments. Length = 3 mm; width = 0.8 mm.

Integument pale yellow, with brownish microsculpture dorsally; thorax and abdomen with brownish dorsal and lateral sclerites; dorsolateral abdominal tubercles dark yellow to brown; ventral region almost white. Head dark brown. Legs slightly sclerotized, dark.

Head hypognathous ( Figs. 20, 21 , 24, 25 ), wellsclerotized, rounded anteriorly, forming short posterior projection on each epicranial plate (in dorsal view), slightly inserted into prothorax. Epicranial suture distinctly Y-shaped. Coronal suture short (1/5 length of head). Frontal sutures pale, broadly diverging from base, arched, reaching antennal sockets. Endocarina forming black line running from junction of coronal and frontal sutures to transverse frontoclypeal suture, altogether forming black T-shaped structure. Each epicranial plate with 2 spatulate setae along frontal suture, 1 on basal third, 1 almost medially; 4 microsetae arranged in oblique, irregular row from posterior region to frontal suture; 4 filiform setae present, 2 on anterior region (1 ventrally), 1 between spatulate setae and 1 on medial region of anterior third; 3 sensilla, 1 situated on posterior region close to microsetae, 1 medially close to frontal suture and 1 anteromedially on outer region. Stemmata absent. Frons with pair of long spatulate setae and pair of sensilla, 1 on each side of endocarina; 1 pair of short digitiform setae close to endocarina; 2 pairs of filiform setae present, both almost on frontoclypeal suture. Base of antennae with 3 filiform setae. Clypeus transverse, concave medially, lateral margins rounded, bearing pair of short filiform setae on each side. Labrum ( Fig. 28 ) transverse, darker and narrower than clypeus, anterior margin concave, nterior angles rounded, bearing a filiform seta on each side and 2 filiform setae medially.

Antenna reduced, articulation area prominent, strongly convex, membranous, situated at ends of fontal suture, slightly sclerotized at base; 3-segmented, antennomere 1 partly membranous, antennomere 2 narrow, slightly sclerotized, bearing 4 sensilla, antennomere 3 conical. Mandibles symmetrical ( Fig. 26 ), palmate; 4-toothed, inner tooth small, slightly rounded, other teeth robust, black, heavily sclerotized, penultimate tooth longer than others. Penicillus formed by 4 digitiform penicillar setae. Two mandibular setae present on outer mandibular base. Maxilla elongate, slightly wider posteriorly; cardo short, subtriangular, bearing 1 posterior filiform seta. Stipes and palpiger bearing pair of filiform setae. Maxillary palpi with 3 palpomeres; basal and 2 nd palpomeres bearing pair of filiform setae, 1 anterolateral and 1 medial; distal palpomere conical, longer than 2 preceding palpomeres combined, bearing sensillum medially. Palpiger bearing 2 filiform setae ventrally. Galea not distinctly separated from lacinia, both represented by 2 palpus-like projections formed by 2 palpomeres, surrounded by many thick, spiniform setae. Labium as long as maxilla, formed by single sclerite, bearing pair of long setae medially, 2 pairs of microsetae close to medial filiform setae, 1 pair of short setae posteriorly and 1 pair of short setae at base of palpi. Labial palpi with 2 palpomeres, apical palpomere elongate, conical, bearing sensillum.

Prothorax narrower and darker than following thoracic segments ( Figs. 20, 21, 22 ). Pronotum transverse, subrectangular, anterior margin wider than posterior margin, lateral margins slightly rounded, anterior angles rounded; dorsal sclerite well-developed, divided by lighter ecdysial line medially, bearing 7 large, hollowed, spatulate setae and 3 microsetae (on each half), arranged as follows: 3 large, hollowed, spatulate setae on anterior margin, 2 on lateral margin (1 at anterolateral corner) and 2 medially, with 3 microsetae in between. Anterolateral sclerite of prothorax small, subquadrate, close to dorsal sclerite, bearing 2 filiform setae.

Meso- and metathoraces narrower and slightly wider than prothorax ( Figs. 20, 21, 22 ). Mesonotum with 4 dorsal, 2 dorsolateral (1 on each side), and 6 lateral sclerites (3 on each side), laterocentral sclerite larger than others. One large, hollowed, spatulate seta on each dorsal sclerite; 3 large, hollowed, spatulate setae on each dorsolateral sclerite; 1 filiform seta on each anterolateral and posterolateral sclerite and 3 large, hollowed, spatulate setae on centrolateral sclerite. Mesothoracic spiracle annuliform, relatively large, emerging from anterolateral mesothoracic sclerite. Metathorax similar to mesothorax, without spiracle. Pro-, meso- and metasterna with medial tubercle, each bearing 1 pair of filiform setae, integument microsculptured.

Legs slightly sclerotized, 5-segmented, similar in form ( Figs. 21, 22 , 30 ). Prothoracic legs smaller than meso- and metathoracic legs. Procoxae narrow, with 2 dorsal sclerites (anterior sclerite slightly darker), each sclerite bearing 1 filiform seta, anterior sclerite also with 2 microsetae. Meso- and metacoxae each bearing 1 filiform seta and 3 microsetae. Trochanters each broadly trapezoidal, membranous, with lateral margins slightly sclerotized; protrochanter bearing 4 filiform setae, 2 of them shorter, and 3 microsetae; meso- and metatrochanters each bearing 3 filiform setae, 1 of them shorter, and 3 microsetae. Femur slightly sclerotized, bearing 8 filiform setae, 4 of them short. Tibia slightly sclerotized, slightly longer than femur, enlarged at base, decreasing in size towards apex, bearing 8 filiform setae (5 dorsal and 3 ventral). Tarsungulus sclerotized, moderately curved; pulvillus bladderlike, as long as tarsungulus.

Abdominal segments I–VII with 14 sclerites forming small tubercles ( Figs. 20, 21, 23 , 29 ); 4 dorsal sclerites present (1 anterior, subrectangular, and wide, 3 posterior, central sclerite subquadrate and larger than lateral sclerites), each bearing 2 hollowed, spatulate setae; 6 rounded dorsolateral sclerites (3 on each side) bearing 2 filiform setae each, with 2 anterior sclerites darker than 2 nd segment; 4 lateral sclerites (2 on each side), smaller sclerite bearing spiracle, larger sclerites bearing 6 filiform setae each. Segment VIII narrower than previous segments, dorsal sclerite covering almost all dorsal portion, darker posterolaterally, bearing 3 filiform setae on each part; 2 ventrolateral sclerites (1 on each side) bearing 6 filiform setae. Circular hollow (maybe a glandular opening) present on segments I–VII between dorsolateral sclerites. Segment IX dorsally forming individual semicircular pygidium with 6 filiform, long setae. Segment X not visible in dorsal view, bearing pygopod. Spiracles present on segments I–VIII, similar to mesothoracic spiracles but smaller, between dorsolateral and lateral sclerites. Segments I–VIII each with 2 ventrolateral tubercles, outer tubercle larger and bearing 6 filiform setae (posterior seta longer), inner tubercle bearing 5 filiform setae (posterior seta longer). Venter of segments I–VIII with grooves delimiting anterior and posterior areas; anterior area bearing 2 filiform setae, posterior area bearing pair of filiform setae on each lateral margin. Segment IX with ventral region similar to dorsal region in form and chaetotaxy.

Larval Variation. We observed variation in the number of large, hollowed, spatulate setae on the pronotum. A single specimen (not illustrated here) has eight large, hollowed, spatulate setae arranged as follows: three on the anterior margin, two on the lateral margin, one almost medially and two close to the posterior margin. The specimen illustrated in Fig. 22 has only one seta close to the posterior margin, so there are seven large, hollowed, spatulate setae on each side of the pronotum.

Description of Pupa. Body 1.7 mm long, slightly bent in lateral view, cream in color, bearing long, brownish setae inserted in small tubercles. Head invisible from above, bearing long and short setae. Prothorax bearing 4 pairs of dorsal setae and pair of setae on lateral callosities; meso- and metanota bearing 2 pairs of setae each; each femur bearing a pair of setae near apex. Abdominal segments I–VI bearing dorsal setae; segment IX with 2 distal projections, each bearing a stout seta on apex ( Fig. 31 ).

Host plants. Larvae and adults were observed consuming the liverwort Reboulia hemisphaerica (L.) Raddi ( Aytoniaceae ) ( Fig. 34 ) and gametophytes of the moss Weissia controversa Hedw. (Pottiaceae) ( Fig. 33 ). Adults were also observed eating capsules (sporophytes) of Weissia sp.

Faunal Associates. Moss samples containing D. borealis were also inhabited by mites, collembolans, spiders, staphylinid beetles, flies (tipulids, sciarids, and ceratopogonids), wasps (chalcidoids and braconids, not clearly associated with particular host species), and moths ( Scoparia sp. , Bryotropha sp. , and Microcrambus elegans (Clemens)) .

Other Biological Observations. Larvae were encountered from mid-January to mid-May. Adults were encountered from mid-March to June (moss typically desiccated in the field in summer through autumn, and adults were then not found even after soaking rains). Inactive larvae may be found curled up in the soil under moss clumps in a small chamber. Larvae near pupation readily succumb to white mold in culture. Larvae move slowly and will curl into a C-shape when disturbed. Adults also move slowly but are capable of jumping when disturbed (though they do not always do so). Mating or egglaying was not observed. No parasitoids were unambiguously associated with D. borealis .

Comments. Distigmoptera borealis larvae are free-living, inhabiting moss cushions and eating bryophytes and marchantiophytes ( Fig. 35 ). Morphologically, they are similar to free-living larvae of Pseudolampsis Horn , Altica Geoffroy , and Ivalia Jacoby , owing to the eruciform habitus, short coronal suture with the frontal sutures diverging and reaching the antennal sockets, sclerotization of the tubercles, absence of highly elongate tubercles, and presence of a specialized granular integument between the tubercles (Casari and Duckett 1997; LeSage and Zmudzinska-Krzesinska 2004; Duckett et al. 2006). Among these genera, only Pseudolampsis and Distigmoptera belong to the subtribe Monoplatini . Larvae of these two genera share the presence of dorsolateral openings on abdominal segments I–VIII, probably associated with some glandular secretion. However, D. borealis differs from Pseudolampsis in that the mandibles are four-toothed with four digitiform penicillar setae (five-toothed mandibles with penicillus formed by ramified setae in Pseudolampsis ), the cardo has one posterior filiform seta (seta absent on cardo in Pseudolampsis ), and the head lacks stemmata (one pigmented stemma on each side in Pseudolampsis ).

In addition to the similarity mentioned above, larvae of D. borealis , Altica , and Ivalia also share the absence of stemmata, the shape of the endocarina, and the number of large setae on the pronotum (LeSage and Zmudzinska-Krzesinska 2004; Duckett et al. 2006). However, these larvae differ in the presence of glandular openings in D. borealis (absent in Altica and Ivalia ) and in the form of their large setae: D. borealis has hollowed, spatulate setae in the dorsal, dorsolateral, and lateral regions; Altica has capitate and hollowed, capitate setae on the dorsum, lateral areas, pronotum, legs, and postcephalic sclerites; the setae in Ivalia are all capitate and located dorsally on the abdomen.

Other described larvae of Alticini, such as Walterianella bucki Bechyné, 1956 (Duckett 2002) and Alagoasa januaria Bechyné, 1955 (Duckett and Swigoňová 2002), both external leaf-feeding species belonging to the subtribe Oedionychina , are very distinct, mainly due to the presence of prominent tubercles on the body.

Material Examined. Holotype, male, 1) Swift Current, Brit. Amer. Sept. 1882 ( C. V. Riley collection); 2) Distigmoptera borealis Blake ; 3) Type No 56748 USNM ( USNM) . Paratypes: same labels as holotype (8 USNM) .

CANADA: ALBERTA 1) Edmonton. Alta. 4.X.1917 F. S . Carr ; 2) male; 3) Hypolampsis pilosa (Ill.) det. by 19. L. G . Gentner ; 4) Distigmoptera borealis Blake (1 male USNM) . ONTARIO 1) Rondeau Pk. ONT, 1-5.IX.1985 L . LeSage & A . Woodliffe ; 2) Distigmoptera borealis Blake Det. L. LeSage (1 USNM) . QUÉBEC 1) Duparquet Que. , 1.IX.1936 G . Stace Smith; 2) On rain pond; 3) 15861. (1 USNM). The same label except 31.VIII.1936 (1 USNM) . USA: COLORADO 1) Col. Nunn Pawnee Grassland Pasture, Owl Creek , 23.XI.1971; 2) Distigmoptera borealis Blake det. R . White , 1972 (1 USNM) . IOWA 1) Iowa City In , IX.3.17 L . Buchanan (9 USNM) . INDIANA 1) So. McAlester Ind. T . June 11, Wickham; 2) Wickham Collection 1933 (1 USNM) . KANSAS 1) Russel Co, Kansas (1 USNM). 1) Topeka Ks, Popenoe (1 USNM). 1) Reno Co. Ks, IX.15.41; 2) R . Schwitzgebel Coll ; 3) 16; 4) H. S . Barber (1 USNM) . MICHIGAN 1) Higgins Lake, Mich. 29 July 1923 L. G . Gentner ; 2) L. G . Gentner Collection (20 USNM). Some with label ‘‘ Hypolampsis pilosa L.G.G Ill ”. 1) Marquette 1.8. Mich. ; 2) Coll Hubbard & Schwarz (7 USNM) . MONTANA 1) Wyo, Colstrip , MT TER / Q31 , Qick trap 2, VII.5.197; 2) J . Leetham Collector ; 3) CHRY D180 ; 4) M55 (1 USNM) . 1) Colstrip , MT., TER / Q31 , soil core VI.29.1974 AGSH; 2) J. Leetham Collector ; 3) MALA 02 ; 4) M97 (1 USNM) . NEW YORK 1) Ithaca N. Y ., 4 July 04 (1 USNM) . NORTH DAKOTA 1) North Dakota: Mercer CO., T144 N, R84 W, S22 , July 5-7, 1972, A. C. F . Hung (1 USNM) .

Figures

Fig. 1. Distigmoptera borealis, dorsal habitus.

Figs. 2–9. Distigmoptera borealis. 2) Dorsal habitus; 3) Lateral habitus; 4) Head, frontal view; 5) Head and pronotum; 6) Pronotum, right anterolateral corner; 7–8) Female abdomen, dorsal and ventral views, respectively; 9) Left elytron.

Figs. 10–19. Distigmoptera borealis. 10) Mesotergite; 11) Metatergite, C1–C3 and D ridge numbers according to Konstantinov (1998); 12) Meso- and metasternites; 13) Metendosternite; 14) Middle leg; 15) Hind leg; 16) Median lobe of aedeagus, dorsal, ventral, lateral, and dorsal views, respectively; 17) Spermatheca; 18) Tignum; 19) Vaginal palpi.

Figs. 20–23. Distigmoptera borealis, larva. 20) Dorsal habitus; 21) Lateral habitus; 22) Thoracic segments; 23) Abdominal segments.

Figs. 24–30. Distigmoptera borealis, larva. 24) Head, 3/4 view; 25) Head, frontal view; 26) Mandibles; 27) Labium; 28) Labrum; 29) Apical abdominal segments; 30) Leg.

Figs. 31–35. Distigmoptera borealis. 31) Pupa, dorsal, lateral, and ventral views, respectively; 32) Larval habitat; 33) Mostly Weissia with assorted vascular plants; 34) Mostly Reboulia (flat green), Weissia, other assorted bryophytes, and Nostoc sp. (Nostocaceae; dark, black, never observed in culture, so it could not be determined if there was any flea beetle feeding on it); 35) Larva feeding on Weissia controversa.