Moiradiomus, Vandenberg & Hanson, 2019

Vandenberg, Natalia J. & Hanson, Paul E., 2019, Overview of the lady beetle tribe Diomini (Coleoptera: Coccinellidae) and description of a new phytophagous, silk-spinning genus from Costa Rica that induces food bodies on leaves of Piper (Piperaceae), Zootaxa 4554 (1), pp. 255-285 : 264-271

Moiradiomus gen. nov.

( Figs. 6, 8, 10 , 13–20 , 23 , 25–42 )

Type species: Moiradiomus clotho sp. nov.

Diagnosis. Distinguished from other members of the tribe Diomini by the combination of morphological, anatomical, and behavioral traits: antenna consistently comprised of 10 antennomeres, distal antennomere not greatly enlarged or elongated relative to penultimate, pronotal anterolateral angles lacking submarginal carinae ( Figs. 13–20 ), prosternum ( Figs. 25–28 ) shaped like a short stemmed Y, short anterior to coxal cavities, about ½ diameter of cavity, with carinae of intercoxal process extending to anterior margin, male genitalia ( Figs. 29–32 ) with basal lobe (=penis guide) asymmetrical ( Figs. 29b, 30b, 31b, 32b ), penis (=siphonal) capsule ( Fig. 10 ) well developed, with inner and outer arms broadly joined into single wedge-shaped structure with sinuous distal margin, capsule enclosing ejaculatory duct prior to its entry into the main penis tube, penis apex lacking flagellum ( Figs. 8 , 29c, 30c, 31c, 32c ), larva silk spinning, adult and larva phytophagous, parasitic on plants in the genus Piper , inducing and feeding on Piper food bodies.

The reduced number of antennomeres (10 as opposed to 11) will distinguished the new genus from all other Diomini except Decadiomus and a few species or individuals presently classified in Diomus. From these latter two genera, Moiradiomus can be distinguished by the highly consistent configuration of the penis of the male genitalia (as described above), and by the unusual life history and trophic relations shared by its members. Thus far the known Moiradiomus species all have a similar elytral color pattern ( Figs. 13–20 ) consisting of a medium to dark brown background with apex suffusely lightened or bearing a distinct band of pale yellow. The elytral color patterns in Decadiomus are more variable, with either a dark or light background and often with contrasting maculae. The tarsal claw is sexually dimorphic in the known species Moiradiomus , but this characteristic occurs in some Diomus and Decadiomus as well.

Description. Form ( Figs. 13–20 ) broadly oval to elongate, length 1.1–2.0 mm, weakly to moderately convex, pubescent. Color pattern simple, unsaturated; predominantly brown with yellow; female pronotum generally darker than in male. Head transverse; eyes finely facetted, well separated dorsally, bearing interfacetal setae, with interocular distance greater than eye width in frontal view, weakly emarginated near antennal insertions by small rounded eye canthus; antenna short, approximately ½ head width, clavate, composed of 10 antennomeres with last 4 or 5 forming irregular club; scape normal; pedicel bead like, slightly narrower than scape; antennomere 3 elongate, longer than 4, with distal antennomere subequal to or only slightly longer than penultimate. Mandible ( Fig. 23 ) with bifid apex, with about 40 minute blunt teeth on incisor blade; molar part with curved tooth near top (=basal tooth sens. Ślipiński 2007). Maxillary palp with 4 palpomeres; terminal palpomere moderately to strongly expanded distally. Labial palp with 3 palpomeres.

Pronotum transverse, evenly convex, base with raised border; pronotal anterolateral angle lacking submarginal carina. Elytron with raised lateral ridge; epipleuron narrow, oblique, not excavated to receive femoral apices, not reaching elytral apex. Prosternum ( Figs. 25–28 ) shaped like short stemmed Y, short anterior to coxal cavities, about ½ diameter of cavity, with carinae of intercoxal process extending to anterior margin or nearly so. Mesoventrite with raised anterior border, with anterior face excavated to receive apex of prosternal intercoxal process. Tibial spurs lacking; tarsal claw sexually dimorphic in species thus far known, with short triangular tooth in female, longer scythe-like tooth in male. Abdomen with 6 ventrites in both sexes; abdominal postcoxal line curving posterolaterally, merging with posterior margin of ventrite. Male genitalia ( Figs. 29–32 ) with outer margin of paramere densely setiferous; setae long, slender, flexible; basal lobe (=penis guide) asymmetrical, penis capsule ( Fig. 10 ) well developed, with inner and outer arms broadly joined into single wedge-shaped structure with sinuous distal margin, capsule enclosing ejaculatory duct prior to its entry into main penis tube; penis apex lacking flagellum. Female genitalia ( Fig. 6 ) with spermathecal capsule fully developed, bent in basal 1/2 with bulbous base; sperm duct moderately long with sclerotized distally tapered sheath enclosing basal 1/2.

Larva, final (4 th) instar ( Figs. 33–39 , based on M. lachesis ). Body off white, pruinose, soft-bodied, subovate, weakly convex dorsally, setiferous. Setae ( Fig. 37 ) minutely barbed, of variable form, some flattened, scale-like, falcate, spatulate, clavate or frayed. Head tapered anteriorly, bearing three stemmata on each side behind antenna; frontal arms of epicranial suture indistinct; epicranial stem absent; mandible ( Fig. 36 ) falciform, with unidentate apex, shallow incisor groove, triangular plate-like angulation near middle of incisor edge, with simple rectangular molar region.

Antenna ( Fig. 35 ) 3-segmented, short; scape annular; pedicle narrower, nearly as long as wide, bearing conical sensorium, pair of preapical setae present; flagellum with long apical seta. Mala small, apically rounded. Maxilla ( Fig. 34 ) with two conspicuous long setae on fused cardo/stipes; maxillary palp 2-segmented; maxillary palpifer incompletely annular. Labial palp 2-segmented; palpifer unsclerotized, indistinct. Fused submentum/mentum with several long conspicuous setae. Leg well developed, visible in dorsal view; tibiotarsus ( Fig. 38 ) with cluster of capitate setae near apex; tarsungulus ( Fig. 39 ) with broad base, pointed apex, bearing single short simple seta at base of concave inner side. Paired dorsal abdominal glands not evident, possibly vestigial or absent.

Trophic relations. Larvae develop on food bodies of Piper species. Although the four species described below are all from Costa Rica, the distinctive larval tents have been observed on leaves of Piper as far north as San Martin Tuxtla, Veracruz, Mexico, and as far south as Itacolomi State Park in Minas Gerais, Brazil.

Etymology. Moiradiomus (gender Masculine) formed from a combination of Moira (=fate) + Diomus (a genus of lady beetle, possibly in reference to Greek mythology where Diomus was an Athenian hero, son of Colyttus, and a companion of Heracles). Moira is an Ancient Greek word (µoῖρα) meaning a portion or lot of the whole. In Greek mythology the Moirae are the three fates, daughters of Zeus and Themis, who spin, measure, and cut the thread of life.

Remarks. The relationships between the new genus and other genera of Diomini (sens. nov.) remains a mystery. Adult members of Moiradiomus key to Decadiomus in Gordon (1999) because the antenna is composed of 10 antennomeres. However, individuals with only 10 antennomeres were also noted to randomly occur in certain Australian Diomus species ( Pang & Ślipiński 2009). The female genitalia of Moiradiomus are quite different from members of Decadiomus and instead match those of Heterodiomus spp. ( Gordon 1999; Gordon & González 2003). The larva of the new genus differs greatly from the unusual onisciform larva of two myrmecophilous species, Diomus thoracicus (type species of Diomus) and Diomus lupusapudoves Vandenberg et al. (Vandenberg et al. 2018) , but is similar to the setiferous, spindle-shaped forms found in Diomus terminatus (Say, 1835) ( Hentz & Nuessly 2002, Akbar et al. 2009) and D. roseicollis (Mulsant, 1853) ( Rees et al. 1994) , as well as Decadiomus pictus Chapin, 1933 ( Böving 1933) . Moiradiomus larvae also appear to lack the dorsal intersegmental glands reported in Diomus and Decadiomus larvae ( Rees et al. 1994; Vandenberg et al. 2018). These glands have been shown to have a repellent effect on ants or play a role in chemical mimicry and are identified by Seago et al. (2011) as an important step in the transition to feeding on ant-protected prey. Presumably they have been rendered obsolete by the enclosed environment provided by the woven larval tent of Moiradiomus .

Figures

FIGURES 3–12. Genitalia of Diomini and Selvadiina (Hyperaspidini): 3–6, female genitalia, dorsal view (spermatheca shaded gray): 3, Selvadius nunenmacheri Gordon 1970 (Hyperaspidini: Selvadiina), showing distal end of sperm duct and spermatheca, accessory gland not shown (after Gordon 1985); 4, Erratodiomus brindisi Gordon 1999 (Hyperaspidini: Selvadiina), bursa through spermatheca, accessory gland not shown (after Gordon 1999); 5, Decadiomus hughesi Gordon & Hilburn 1990 (Diomini), bursa through spermatheca (note long convoluted sperm duct); 6, M. lachesis (Diomini) (A.g.= accessory gland); 7–12, male genitalia of Diomini, left lateral view of penis: 7, D. hughesi; 8, M. lachesis; 9, Diomus donatus Gordon (capsule); 10, M. lachesis (capsule); 11, Decadiomus bigemmeus (capsule); 12, Decadiomus liebecki (capsule)

FIGURES 13–16. Moiradiomus species habitus illustrations. 13, M. clotho: holotype, male; 14, M. clotho: paratype, female. 15, M. lachesis: holotype, male; 16, M. lachesis: paratype, female. Scale bar = 0.5 mm.

FIGURES 17–20. Moiradiomus species habitus illustrations. 17, M. atropos: holotype, male; 18, M. atropos: paratype, female. 19, M. nanita: holotype, male; 20, M. nanita: paratype, female. Scale bar = 0.5 mm.

FIGURES 21–24. Dorsal view of right mandible: 21, Subcoccinella vigintiquatuorpunctata (L.) (folivorous) (after Kovář 1996); 22, Bulaea sp. (omnivorous with emphasis on pollinivory/phytophagy); 23, Moiradiomus lachesis (enlarged detail of apical portion of incisor blade shown to left of main structure) (specialized on Piper food bodies); 24, Adalia bipunctata (entomophagous with emphasis on aphids) (after Kovář 1996).

FIGURES 25–28. Diagrammatic ventral view of Moiradiomus prosterna (setae, color patterns, and surface punctation not indicated): 25, M. clotho; 26, M. lachesis; 27, M. atopos; 28, M. nanita.

FIGURES 29–32. Male genitalia of Moiradiomus species (a, left lateral view of phallobase; b, ventral view of phallobase; c, left lateral view of penis; d, apex of basal lobe, enlarged): 29, M. clotho; 30, M. lachesis; 31, M. atopos; 32, M. nanita.

FIGURES 33–39. Fourth instar larva of Moiradiomus lachesis: 33, dorsal habitus view, scale bar = 0.5 mm; 34, ventral view of mouthparts, enlarged; 35, right antenna, enlarged; 36, dorsal view of right mandible, enlarged; 37, diverse dorsal setae, enlarged; 38, tibiotarsus showing distribution of clavate setae, enlarged; 39, apex of tibiotarsus (setae removed) showing shape of tarsal claw, enlarged.

FIGURES 40–42. Tents of Moiradiomus spp.: 40, M. lachesis on Piper lanosibracteum; 41, M. nanita on P. reticulatum; 42, M. atropos on P. friedrichsthalii.