Abachrysa eureka (Banks)

Tauber, Catherine A., Kilpatrick, Shelby Kerrin & Oswald, John D., 2020, Larvae of Abachrysa eureka (Banks) (Neuroptera: Chrysopidae: Belonopterygini) descriptions and a discussion of the evolution of myrmecophily in Chrysopidae, Zootaxa 4789 (2), pp. 481-507 : 483-496

Descriptions of the Immature Stages of Abachrysa eureka (Banks)

Egg ( Fig. 1 )

Length 3.0 mm, width 1.1 mm (n = 1); fusiform, with apical pole bearing micropyle; laid singly on an erect, smooth, shiny stalk. Stalk 9.2 mm long (n = 1); sticky, but without fluid droplets. Catanach (2007) provided additional measurements (see Table 1).

Catanach (2007) stated that eggs were pale blue-gray if fertile, but light green if infertile. Subsequent work has shown that eggs are light green when laid; if fertile and healthy, they assume a pale bluish-gray color as the embryo becomes visible beneath the chorion.

First instar ( Figs 2–9 )

Body. Small, compact, slightly thickened dorsoventrally through mesothorax, metathorax, and anterior abdominal segments, but dorsal surface probably not abruptly elevated; length of shriveled, unfed specimens slightly greater than 1.5 mm. Integument smooth, without microtrichia, bearing four types of setae: (i) moderately long to medium length, stout, slightly denticulate, with acute tip (primary cephalic setae); (ii) long, robust, lightly denticulate to smooth, straight-to-curved basally, curved-to-bent distally, with acute apex (most setae on the lateral and laterodorsal tubercles of the thorax and abdomen; LS, LDS); (iii) very long, slender, smooth, curved submedian setae (SMS) on dorsum of mesothorax, metathorax, and first to sixth abdominal segments; (iv) short to medium length, straight, smooth, with acute tip (some primary setae on the cranium, pronotum, seventh and eighth abdominal segments). The SMS are extremely tapered and thin distally; it is difficult to determine if the tips of these setae are acute or minutely hooked.

Cranium ( Figs 2–5 ). Width 0.54–0.55 mm; length ~ 0.46–0.47 mm. Dorsum smooth, well sclerotized; posterior margin quadrate, partially withdrawn into cervix (larva at rest); anterior region beneath base of antenna forming pedicellate extension, capable of receiving retracted base of scape. Six stemmata, all well separated, relatively small. All primary cephalic setae (S1–S12) present, with acute tips ( Figs 4 , 5 ). Dorsal setae (S1–S7, S11, S12) with surface slightly denticulate; S11, S12 robust, long, directed anteriorly; S1, S2, S3, S6 medium length, robust, but slightly more slender than S11, S12; S5 relatively small; Vx with three short setae, pore detected on some specimens; anterior region of cranium (anterior to S11) with two pairs of small, smooth, acute setae (possibly S14-cl, S15-cl of V. elegans ); anterior tip of clypeus with pair of large, lightly denticulate, acute setae projecting anteriorly (possibly S13-cl of V. elegans ). Venter with cardo and stipes narrow, elongate, rectangular; primary setae (S8–S10) smooth, short to medium length; S8 posterior to eye (sometimes near cardo); S9, S10 near each other, medial to eye. Ventral midregion with ~three pairs of setae on or near mentum; base of palpiger with single seta.

Cephalic appendages ( Figs 4–6 ). Clypeus large, extending laterally toward base of mandibles; anterior margin extending forward as truncated process. Mandible short, stout, heavily sclerotized, especially at tip and along lateral margin of distal half; 0.35–0.39 mm long; 0.11–0.13 mm wide, at base; with sharply acute tip, ~7–8 acute teeth in saw-like row along inner edge just below apex. Maxilla broad basally, with two short basolateral setae; lateral margin with two acute teeth (spurs) near terminus, basal one small, pointed basally, distal one larger, near terminus, pointed apically; tip rounded, heavily sclerotized, with small patch of microsetae. Labial palp extending to tip of mandible or slightly beyond; second segment broad (~ 0.05 mm wide at widest point; ~ 0.10–0.12 mm long), with three to four annulations; terminal (third) segment rounded, tapering distally, terminus with small, pale, round projection bearing ventral pore and several microsetae apically; maximum width of terminal segment approximately one-half maximum width of second segment. Basal (first) palpal segment with two pairs of long distal setae, one lateral, one mesal; terminal annulation of middle segment with two long setae near apex, one lateral, one mesal. Antenna 0.35–0.38 mm long; scape set within pedicellate cranial extension, heavily sclerotized, rounded, tubular, straight sided, with sharp projection on lateral base; pedicel elongate, tapering, with ~five or six rounded annulations on basal half, with irregular annulations on distal half. Flagellum round in cross section, narrow, tapering to slender, bifurcated terminus; base with lateral spur; spur sheath-like, slender, elongate, wrapped partially around flagellum, extending distally almost to terminus of flagellum, closely pressed against lateral margin of flagellum (often difficult to see); terminus with two elongate (length up to 0.1 mm), very fine terminal setae extending anteriorly, then curving toward each other, with mesal seta usually longer than lateral one.

Cephalic coloration ( Figs 2 , 3 , 6 ). Anterodorsal surface of cranium entirely dark brown, becoming pale near posterior margin (normally concealed within cervical membrane), no specific cephalic markings distinguished; integument around and between stemmata dark brown; pedicellate cranial extension dark brown dorsally, pale ventrally. Venter with cranial margin, sclerites dark brown; intersegmental membrane pale. Antenna with scape, base of pedicel dark brown; pedicel with annulations brown basally, lighter brown distally; flagellum light brown to amber. Mandible and maxilla brown basally, light brown to amber distally. Labial palp with basal segment dark brown; annulations of second segment brown, membrane between annulations pale; distal segment brown basally, becoming lighter brown to amber distally.

Thorax ( Figs 6 , 7 ). Each segment with pair of broad, thick, palmate, lateral tubercles (LTs); distal margin of each LT with robust chalazae bearing prominent setae (LS); LS long, robust, denticulate, with distal region usually bent at 90° angle, with tip stout, straight, unhooked; sclerites not distinguished. Prothorax with dorsal surface dark brown, smooth, probably well sclerotized throughout, having sparse setae, no microsetae; each LT with seven to eight LS, anterior LS extending above head well beyond posterior margin of eyes; pronotal setae medium length (not extending beyond segmental margin), smooth, straight, with acute (unhooked) tips, arising from small chalazae: three short setae mesal to each LT, two medium-length setae anteromesal to base of each LT, one pair of shorter setae between them, two pairs of short setae posteriorly. Mesothorax, metathorax with dorsal surface having dense covering of submedian setae (SMS), no microsetae; LTs similar to those on prothorax, each bearing eight to ten long LS; laterodorsal tubercles (LDTs) absent; SMS arranged in two broad bands across surface of each segment; SMS very long, slender, smooth, extending anteriorly from small chalazae. Mesothoracic spiracle very small, oblong, sessile, located near anteromesal base of LT; spiracular seta (SSp) not identified.

Leg ( Figs 6 , 8 ). Brownish distally, pale basally; setae smooth, with acute tips. Coxa elongate, trochanter triangular, both with few setae; femur with moderately dense setae; tibia with numerous setae, separate from tarsus; tarsus short, with two setae at tip, above claws; tarsal claws slender, deeply cleft; empodia long, with stiff, elongate bristle beneath.

Abdomen ( Figs 6 , 9 ). First segment (A1) short, narrow, with no spiracle, LT, or LDT; dorsum with transverse band of dense SMS arising from small chalazae. Segments A2–A5 more robust (longer, broader) than A1, each bearing pair of bulbous LTs, round spiracular opening near dorsomesal margin of LT, no laterodorsal tubercles (LDTs). LTs white to cream dorsally, with brown marking on ventrolateral base, visible laterally; each LT with two denticulate LS, no microsetae. Spiracular opening large, round, with well sclerotized ring around margin, with bulbous atrium beneath. Dorsum of each segment with transverse band of dense SMS similar to those on A1. Segments A6–A7 each with LTs, LS, and spiracles similar to those on A2–A5, pair of laterodorsal tubercles (LDTs) near anteromesal margin of LT base. LDTs each bearing two (A6) or three (A7) robust, denticulate, acute, laterodorsal setae (LDS), one long, others short to medium length; segments without microsetae. Dorsal surface of A6 with transverse band of SMS between LTs; posterior section without setae. Dorsum of A7 dark brown, well sclerotized, without elongate, slender SMS as on A1–A6, with shorter, smooth, acute setae as follows: one pair of setae (SSp) associated with spiracles, two pairs of anterior setae between spiracles, two pairs of longer, more robust setae between LTs, single pair of setae near posterior margin. Segment A8 dark brown, well sclerotized dorsally; LT short, bulbous laterally, with robust, denticulate LS—one longer than other; dorsum with two pairs of robust, denticulate setae in midsection between LTs, two pairs of short, smooth, acute setae anterolaterally. Segment A9 tubular, dark brown to black, heavily sclerotized posteriorly; anterior (lighter) section with pair of very small setae; midsection with single pair of long, robust, denticulate setae laterally, pair of white spots (pores) mesal to setae; posterior section with three pairs of long, robust, denticulate setae near posterolateral margin. Segment 10 with large, dark brown to black sclerites; dorsum without setae except for single pair of smooth, acute setae near terminus.

Third instar ( Figs 10–12 )

Bod y. Stocky, globose dorsally, flat ventrally; thoracic, abdominal nota wide, extending fully over sides of body, with LTs extending laterally from ventral margins of nota. Integument of thorax and abdomen with dark transverse (possibly sclerotized) bands, separated by pale bands and intersegmental membrane. Four types of setae: (i) smooth, hooked, as described for I. insignis (covering almost entire exposed dorsal surface of body); (ii) stout, short, straight, with acute tip, possibly with rough surface (on upper surface of head, distal margins of trochanters); (iii) stout, with blunt to acute tip, possibly with rough surface, some curved, others with distal one-third to one-fourth bent almost perpendicularly, as described for I. insignis (on distal margins of LTs of T1–T3, A2–A7); (iv) simple, small, straight, with acute tip (at base of LTs on A7; on dorsum of A8, A9; on venter of A3–A7; on femora, tibiae).

Cranium. Appearing quadrate, but perhaps not as much as in I. insignis ; anterior margin slightly convex; without noticeable markings; dorsal setae dark.

Cephalic appendages. Mandibles short, stout, with acute tip. Antenna filiform, tapering, extending beyond end of mandibles; scape located within sclerotized cranial extension, with stout setae on distolateral margin; pedicel annulated; flagellum tapered, apparently with elongate terminal seta(e), as illustrated by Principi (1944) for I. italica (and broken off of Tauber and Winterton’s specimen of I. insignis ). Cervix dark, probably well sclerotized, at least laterally.

Thorax. Segments broad, dorsoventrally thickened, each with pair of LTs; LTs robust, palmate, rounded distally, with distal margin bearing stiff, robust, bent LS, with dorsal surface bearing sparse, smaller, apparently acute setae; prothorax appearing to have two subsegments, mesothorax with three subsegments, metathorax apparently with one. Legs short, stocky, dark; coxae elongate dorsoventrally, appearing well sclerotized and dark; tarsi particularly short.

Abdomen. Segments A1–A6 broad, thick; together with thorax forming large, densely setose, dorsal arch of body; A1 with only one visible subsegment, without LTs, dorsally about as long and wide as metathoracic posterior subsegment, excluding LTs. Segments A2–A6 each with two subsegments dorsally, subsegments merging above LTs; LTs round, spherical distally, with short base, bearing robust, curved, or bent LS distally, smaller, hooked setae dorsally. Segments A7–A10 with subsegmentation not apparent; each segment narrower than, and probably partially retractable within preceding segment; surfaces with sparse, short, acute setae. A7 with LTs about as long as those on A5 or A6, but much narrower, their apices with dense covering of robust, acute LS extending posteriorly; spiracles near anterior margin of segment. A8 with small lateral LTs bearing short, slender, acute setae; spiracles at base of segment. A9, A10 conical (LTs absent), with short slender, acute setae.

Biology

Little is known about the biology of A. eureka . However, based on our experiences and MacLeod’s notes, we can provide some new information.

Egg stage. Five field-collected females laid 57 eggs, 49 (86%) of which hatched. The eggs were laid between September 19 and October 14, 2015 and hatched in 10 to 14 days (under laboratory conditions).

Larval development. MacLeod’s rearing started with a female specimen that Joseph Sheldon collected on Boot Key, FL (July 25, 1968) and sent to him at the University of Illinois. The specimen laid nine eggs en route by July 30; two were used for chromosome preparations, and four hatched on August 8 and 9. Three additional eggs were laid during the first week of August. MacLeod’s notes do not indicate a hatching date for either the three remaining eggs that were laid before arrival or the three that were laid after arrival. Presumably, they did not hatch.

MacLeod recorded rearing notes for four Abachrysa larvae held in shell vials (25°C, L:D 14:10, 80% relative humidity); all instars fed on the larvae and pupae of the ants that he provided (species not specified), but none ac- cepted aphids, disabled termites, or ether-killed Drosophila . He recorded the following developmental times for the various stages—L1: 15 days (n = 2); L2: 8 and 11 days (n = 2); L3: 28 days (n = 1), mature L3 within cocoon: 10 days (n = 1); pupa within cocoon: 15 days (n = 1, a male that emerged on October 23). One second instar and one third instar were preserved. Unfortunately, the specimens are missing; however, MacLeod made an excellent drawing and took photos of the third instar.

Larval behavior. MacLeod’s notes do not mention that the larvae engaged in “loading behavior”, i.e., the series of movements that debris-carrying chrysopid larvae typically exhibit in order to apply debris to their dorsa.

Adult behavior. MacLeod indicated that adults emit a defensive odor similar to that of many species of green lacewings; he referred to it as a “moderate”, “usual” odor (see Blum et al. 1973). Also, his notes include a photo of a pinned adult A. eureka that he examined at the Museum of Comparative Zoology, Harvard University, Cambridge, MA. This specimen carries a worker ant ( Pheidole sp.) firmly attached to a metathoracic leg ( Fig. 13 ), perhaps indicative of an ant association.

Seasonal emergence. Based on collection records from numerous museums, Catanach (2007) concluded that A. eureka has two peaks of adult emergence, one in the spring and another in the fall. The second emergence appears to be smaller in the southeastern states than in Texas, where it can be substantial.

Figures

FIGURE 1. Abachrysa eureka (Banks), egg (with stalk), lateral. Photo: E. G. MacLeod.

FIGURE 2. Abachrysa eureka (Banks), first instar, head and thorax, dorsal (specimen point mounted). A. Dorsal cephalic setae visible. B. Flagellar setae visible. fls flagellar setae; SMS, submedian setae of thorax; T1-LT, T2-LT, T3-LT, lateral tubercles of prothorax, mesothorax, and metathorax.

FIGURE 3. Abachrysa eureka (Banks), first instar, head (specimen point mounted). A. Lateral view. B. Ventral view. cls, clypeal setae; co, cardo; cr, cranium; cre, pedicellate cranial extension; eye, eye including six stemmata; fl, flagellum; fls, flagellar setae; lp, labial palpus; md, mandible; men, mentum; mx, maxilla; ped, pedicel; pg, palpiger; sc, scape; st, stipes.

FIGURE 4. Abachrysa eureka (Banks), first instar, head. A. Dorsal view (tip of right mandible and labial palps excluded). B. Ventral view (antenna, mandible excluded). cly, clypeus; co, cardo; cr, cranium; cre, pedicellate cranial extension; lp1, lp2, lp3, basal, middle, and distal subsegments of labial palpus; md, mandible; mx, maxilla; pg, palpiger; st, stipes; S1–S12, primary cephalic setae; Vx, three short posterior setae surrounding a pore.

FIGURE 5. Abachrysa eureka (Banks), first instar, cephalic appendages. A. Antenna, dorsal (scape partially withdrawn into pedicellate cranial extension). B. Base of antenna, lateral (scape exerted). C. Mandible, dorsal. D. Maxilla, ventral. cre, pedicellate cranial extension; fl, flagellum; memb, membrane between scape and cranium; ped, pedicel; sc, scape; sp, flagellar spur. Scale bars: upper (C, D), lower (A, B).

FIGURE 6. Abachrysa eureka (Banks), first instar, habitus, lateral (specimen point mounted). cox, coxa; fem, femur; fl, flagellum; fls, two flagellar setae; prn, pronotum; tar, tarsus; tib, tibia; A7, A9, A10, seventh, ninth, and tenth abdominal segments; A4-LT, A6-LT, lateral tubercles of fourth and sixth abdominal segments; T1-LT, T2-LT, T3-LT, lateral tubercles of prothorax, mesothorax and metathorax

FIGURE 7. Abachrysa eureka (Banks), first instar, thorax, dorsal. A. Prothorax. B. Mesothorax and metathorax (SMS more numerous than shown). LS, setae on lateral tubercle; LT, lateral tubercle; SMS, submedian setae; Sp, spiracle. Scale applies to A and B.

FIGURE 8. Abachrysa eureka (Banks), first instar, metathoracic leg, lateral. claw, pretarsal claw; cox, coxa; emp, empodium; fem, femur; s, stiff apical seta; tar, tarsus; tib, tibia; tr, trochanter.

FIGURE 9. Abachrysa eureka (Banks), first instar, abdomen, dorsal. A. First and second segments (SMS more numerous than shown). B. Sixth segment. C. Seventh segment. D. Eighth, ninth, and tenth segments.A1–A10, abdominal segments; LDS, setae on laterodorsal tubercle; LDT, laterodorsal tubercle; LS, setae on lateral tubercle; LT, lateral tubercle; SMS, submedian setae; Sp, spiracle; SSp, spiracular seta.

FIGURE 10. Abachrysa eureka (Banks), third instar.A. Head and thorax, anterior. B. Habitus, lateral (head and apical abdominal segments withdrawn). C. Habitus, dorsal (head and apical abdominal segments extended). Photos: E. G. MacLeod.

FIGURE 11. Abachrysa eureka (Banks), third instar, habitus (walking), lateral. Drawing: E. G. MacLeod.

FIGURE 12. Abachrysa eureka (Banks), third instar, head and thorax, lateral. A1, A2, first and second abdominal segments; T1–T3, first to third thoracic segments; T1-LT, T2-LT, T3-LT, prothoracic, mesothoracic, and metathoracic lateral tubercles. Drawing: E. G. MacLeod.

FIGURE 13. Ant worker (Pheidole sp.) attached by its mandibles to the metatibia of a female A. eureka specimen in the Museum of Comparative Zoology (MCZ). Photo: E. G. MacLeod.