First Evidence of Indirect Oviposition in Phasiinae (Diptera: Tachinidae) with Insights on Leucostoma Meigen, its New Neotropical Distribution, and Host Association

© 2024 Academia Sinica, Taiwan Open Access First Evidence of Indirect Oviposition in Phasiinae (Diptera: Tachinidae) with Insights on Leucostoma Meigen, its New Neotropical Distribution, and Host Association Rodrigo de Vilhena Perez Dios1,* , Talita Roell2, and Graciano Tejada Hurtado3 1Laboratório de Diptera, Museu de Zoologia, Universidade de São Paulo, Av. Nazaré, 481, 04263-000, Ipiranga, São Paulo/SP, Brazil. *Correspondence: E-mail: [email protected] (Dios) 2Laboratório de Hemiptera, Museu de Zoologia, Universidade de São Paulo, Av. Nazaré, 481, 04263-000, Ipiranga, São Paulo/SP, Brazil. E-mail: [email protected] (Roell) 3Laboratorio de Entomología, Centro de Diagnóstico de Sanidad Vegetal, Servicio Nacional de Sanidad Agraria, SENASA, Av. La Molina 1981, La Molina. Lima, Perú. E-mail: [email protected] (Tejada) Received 16 July 2024 / Accepted 19 October 2024 / Published 27 December 2024 Communicated by Daniel Stec Flies of the family Tachinidae are known for being arthropod parasitoids. Phasiinae, the bug-killing flies, is one of its subfamilies, which is specialized in heteropteran hosts (Hemiptera: Heteroptera). Flies of this group are known to oviposit directly on their heteropteran hosts, and many parasitize important agricultural pests, making them relevant for biological control. Among phasiines, the tribe Leucostomatini is easily distinguished by their characteristic female terminalia, which has structures that resemble a pincer. Leucostoma Meigen is the largest genera with 28 species, and only 10 being recorded in the Neotropical Region. Herein, we present the first direct evidence of an indirect oviposition strategy in bug-killing flies. We observed females of Leucostoma acirostre Reinhard ovipositing directly on the host plant of their hosts. This possibility has already been considered in the literature, and a discussion of this new strategy is presented, as it is relevant for understanding Tachinidae evolution, as well as developing biological control strategies. This is the first record of L. acirostre for the Neotropical Region, as well as a new host record for the rhopalid Harmostes parafraterculus Göllner-Scheiding. Alongside, Leucostoma aterrimum (Villers) specimens were collected from Liorhyssus hyalinus (Fabr.) of Peru, an important quinoa pest from the region, and the first record of the species and host association for the country. We update the distribution of both species, with new records for South America. Both species are redescribed, including photographs, new data for the puparium, and male and female terminalia (both illustrated). Lastly, we discuss the validity of the few Leucostoma non-heteropteran host records, as they are all probably mistakes, and comment on the widespread distribution of some of the genus’ species and host use. Key words: Biological control, Distribution, Leucostomatini, Oviposition strategy, Taxonomy Citation: de Vilhena Perez Dios R, Roell T, Tejada G. 2024. First evidence of indirect oviposition in Phasiinae (Diptera: Tachinidae) with insights on Leucostoma Meigen, its new neotropical distribution, and host association. Zool Stud 63:54. doi:10.6620/ZS.2024.63-54. BACKGROUND Among the highly diverse parasitoid flies (Diptera: Tachinidae), the subfamily Phasiinae are known as the bug-killing flies, due to their habit of using different heteropteran insects as hosts (Hemiptera: Heteroptera) (Dupuis 1963; Blaschke et al. 2018). Some phasiines parasitize important crop-pests, including different Trichopoda Berthold species, with potential for biological control strategies; however, many of those still lack basic taxonomical knowledge (Guimarães 1977; Arnaud 1978; Dios and Nihei 2020). Zoological Studies 63:54 (2024) doi:10.6620/ZS.2024.63-54 1 © 2024 Academia Sinica, Taiwan Leucostomatini is a peculiar group among the bug-killing flies that are easily distinguished by their remarkable female terminalia morphology. Many females of this tribe have modified parts of the terminalia which act as pincers and supposedly function to grasp the host (Dupuis 1963). Leucostomatini are usually small to medium-sized flies, with dark or grey coloration, contrary to many other phasiines that have striking coloration and/or hymenopteran mimicry (some exceptions in Leucostomatini are observed in species of Brullaea Robineau-Desvoidy and Clairvillia Robineau-Desvoidy) (Dupuis 1963; Blaschke et al. 2018; Dios and Nihei in prep). As the vast majority of Phasiinae, all Leucostomatini host records are from different families of Heteroptera (Hemiptera): Alydidae, Coreidae, Lygaeidae, Miridae, Nabidae, Pentatomidae, Rhopalidae, and Stenocephalidae (Arnaud 1978; Guimarães 1977; Tschorsnig 2017). Leucostoma Meigen is the most diverse Leucostomatini genera, with 28 species. Curiously, some species, such as Leucostoma aterrimum (Villers) and L. simplex (Fallén) (O’Hara et al. 2020) are widespread globally and probably follow some of their host distribution. Despite their diversity, ten species have been recorded for the Neotropical Region, and only three species have been recorded from Brazil (O’Hara et al. 2020; Nihei et al. 2024). The same scarcity is observed for Neotropical host records, with only three for South America: Epicauta pilme Molina (Meloidae: Coleoptera) for Leucostoma aterrimum, and Oncopeltus fasciatus (Dallas) and O. unifasciatellus Slater (Lygaeidae: Hemiptera) for Leucostoma brasilianum (Townsend) (Guimarães 1977). Despite the characteristic pincer, Leucostomatini females also have the 8th sternite modified as a piercer, and their egg morphology points towards an injectable egg, with a membranous chorion and without a respiratory crypt (Pantel 1910; Dupuis 1963; Gaponov 2003). However, no observation on host oviposition has been made, along with no data regarding the oviposition process or how females use those peculiar pincers and short lance to infect hosts. Here, we present new Leucostoma records for Brazil, L. acirostre Reinhard from São Paulo, SP, and Petrolina, PE, as well as a new host record for the species: Harmostes parafraterculus Göllner-Scheiding (Rhopalidae: Hemiptera). We also present new records of L. aterrimum for Brazil, as well as Peru, where it was found parasitizing Liorhyssus hyalinus (Fabr.) (Rhopalidae: Hemiptera), an important pest of quinoa crops (Chenopodium quinoa Willd.) in the region. Both species are redescribed, with new data on the puparium, along with descriptions and illustrations of the male and female terminalia, complementing previous works (Reinhard 1956). A brief discussion about the validity of all non-Heteropteran Leucostomatini hosts is presented. We also provide new remarkable observations regarding the oviposition behavior of Leucostomatini species. This is the first record of an indirect oviposition strategy in Phasiinae, which could bring light to different uses for the characteristic female terminalia in Leucostomatini and understanding the evolution of oviposition strategies in Phasiinae. MATERIALS AND METHODS All examined material is deposited at the “Museu de Zoologia da Universidade de São Paulo,” São Paulo, SP, Brazil (MZSP) and “Coleção Entomológica do Instituto Oswaldo Cruz”, Rio de Janeiro, Brazil (Jane Costa). The holotype of L. acirostre, deposited at the Smithsonian National Museum of Natural History (NMNH), Washington, DC, USA, was examined by the first author. Morphological terminology follows Cumming and Wood (2017) and puparium follows Ziegler (1998). Photographs of pinned specimens were taken using an AxioCam Mrc 5 camera attached to a Zeiss Discovery V20 stereomicroscope. The images were stacked with the software Helicon Focus 7.5.8, and edited in Adobe Photoshop CS6. Illustrations were made using a camera lucida attached to a Leica MZ16 stereomicroscope, and edited and arranged in Adobe Illustrator CS6. To digest tissues and clear structures, the last abdominal segments were placed in a glass tube containing a 10% KOH solution and heated in water at 70°C for 5 minutes, neutralized in a 5% acetic acid solution, and rinsed in distilled water. After examination, the dissected parts were placed in glycerin inside a plastic microvial pinned with the source specimen. All the behavioral observations and photos were taken by RVPD in a community garden in Santo Amaro’s neighborhood in São Paulo, SP, Brazil, using a smartphone Samsung M31 with an attached macro lens. Some additional distribution records were observed on iNaturalist (2024). RESULTS New distribution records for Leucostoma acirostre and Leucostoma aterrimum Leucostoma acirostre: BRAZIL: Pernambuco, Petrolina, 5 males and 4 females (MZSP); São Paulo, São Paulo, 2 females and 1 male, (MZSP). page 2 of 13Zoological Studies 63:54 (2024) © 2024 Academia Sinica, Taiwan Leucostoma aterrimum: BRAZIL: Rio de Janeiro, Rio de Janeiro, 1 female (CEIOC), São Paulo, São Paulo, Cantareira, 1 female (MZSP), São Paulo, Bebedouro, Andes, 1 male (MZSP). PERU: Arequipa, Santa Rita, 4 males and 5 females (MZSP). New record of Leucostoma acirostre in Harmostes parafraterculus, and evidence of an indirect oviposition strategy One female of L. acirostre (Fig. 2 C, D) was reared from a female Harmostes parafraterculus (Fig. 1) in São Paulo. The larvae emerged on January 30th, 2024, and pupated immediately. The fly emerged on February 9th, 2024. A male (Fig. 2) and another female of L. acirostre were also collected at the same locality and similar date as mentioned above. This is the first host record and the first records (alongside with the specimens from Pernambuco) for the species in South America. Previously, L. acirostre was only known from the Nearctic Region (Reinhard 1956; O’Hara et al. 2020). Observing the behavior of L. acirostre in B. pilosa (Fig. 3), the first author noticed that sometimes the female approached their abdominal rear end to the base of the capitulum in the process of fruiting. One female was photographed during that behavior in São Paulo, Brazil (Fig. 3A). This is a strong indication that these flies oviposit directly on the hemipteran host plant, and not in the host itself. Females also land and walk in buds with developing achenes as well as with fully developed achenes (Fig. 3). More on this behavior is discussed below. Record of Leucostoma aterrimum in Liorhyssus hyalinus (Fabr., 1794) The specimens from Santa Rita, Arequipa, Peru (five females and four males) were reared from Liorhyssus hyalinus collected in quinoa crops (Chenopodium quinoa Willd.) in 2015. Taxonomy: Leucostoma Meigen, 1803: 279. Type species: Ocyptera simplex Fallén, 1815, by subsequent monotypy of Meigen (1824: 234) [Sweden]. For a genus diagnosis and description, see Reinhard (1956), and for a full list of synonyms list, see O’Hara et al. (2020). Leucostoma acirostre Reinhard, 1956 Leucostoma acirostre Reinhard 1956: 162 Diagnosis: The females are easily distinguished from other species of the genus as the tergite 6 pincers structures lack any denticules or strong setae on their inner margin. The males have some silver pruinosity on the abdomen, usually anteriorly on the last segments, as well as in the head. The male terminalia likely have some features that distinguish them from other Leucostoma species, but the single male was not dissected to compare. Redescription: Male (Figs. 2A–B, 3D). Body length 4.5–5.2 mm. Coloration: Head brown to black with strong silver and golden pruinosity; frontal vitta black. Antenna black; arista black. Palpus brown and prementum dark brown. Thorax black with silver pruinosity dorsally and laterally. Thoracic spiracles dark brown. Wing hyaline. Calypters white and partially hyaline. Halter dark brown to black. Legs dark brown to black; claws black; pulvilli pale brown. Abdomen black, tergites 3 to 5 anteriorly Fig. 1. Harmostes parafraterculus. A, dorsal view. B, Lateral view. page 3 of 13Zoological Studies 63:54 (2024) © 2024 Academia Sinica, Taiwan with silver pruinosity forming bands, stronger laterally. Head: Holoptic. Eye bare. Frontal vitta narrow, slightly narrower than fronto-orbital plate maximum width. Ocellar setae lateroclinate. Eight frontal setae, descending to pedicel level. Inner and outer vertical setae hair-like, similar to surrounding postocular setae. Postocellar setae hair-like. Antenna inserted at middle level of eye, short, not extending to vibrissa level. Lunule setulose. Scape short, about one-quarter length of pedicel. Pedicel setose dorsally, with 1 strong seta. First flagellomere slightly longer than pedicel, elliptical but broader distally. Arista micropubescent. Parafacial bare. Vibrissa strong, 4–5 subvibrissal setae. Eye about 0.85 to 0.9 head height. Gena about 0.1 to 0.05 eye height. Antennal axis slightly shorter than oral axis. Lower facial margin protruding. Palpus slightly clavate. Prementum long, slightly longer than head height. Labella well-developed, as long as first flagellomere. Thorax: Prosternum bare. Proepisternum bare. One strong proepimeral seta, surrounded with weaker setae. Anterior spiracle with both lappets welldeveloped, covering almost the entire opening. Posterior spiracle with posterior lappet slightly larger than anterior. Acrostichal setae 1+1, with another presutural long setula. Dorsocentral setae 2+3. Intra-alar setae 1+2. Supra-alar setae 1+2, the second postsutural short. Postpronotal lobe with 2 setae, and 3 anterior long setulae. One postalar seta. Scutellum with one basal, one lateral, one short subapical, and one decussate apical pairs of setae. Two katepisternal setae, with posterior seta longer. One anterior and five posterior anepisternal setae. One anepimeron seta. Katatergite and anatergite bare. Wing: subequal to thorax + abdomen length. Ratio of wing length/maximum wing width 2.4. Costal spine not differentiated. Costal vein without breaks, beyond intersection with vein Sc without ventral setulae. Cell r4+5 with long petiole, petiole more than three times r-m length, ending before wing apex. Base of vein R4+5 with 1 dorsal and ventral setae. Crossvein dm-cu slightly curved. Calypters rounded, large, almost Fig. 2. Leucostoma acirostre. A, Male, dorsal view. B, Male, lateral view. C, Female, dorsal view. D, Female, lateral view. Specimens from São Paulo, SP, Brazil. page 4 of 13 Zoological Studies 63:54 (2024) © 2024 Academia Sinica, Taiwan reaching end of syntergite 1+2. Legs: Fore coxa with many anterodorsal setae. Fore femur with row of posterodorsal and posteroventral seta. Fore tibia with one posteroventral seta. Mid coxa with row of setae on anterior surface. Mid femur with rows of anteroventral and posteroventral setae on basal half, two posterodorsal preapical and one posterior preapical setae. Mid tibia with three anterior, two posterodorsal and one ventral setae. Hind coxa with row of anterodorsal setae. Hind femur with rows of anterodorsal, anteroventral and posteroventral setae on basal half, two anteroventral preapical setae. Hind tibia with three anteroventral setae, row of anterodorsal short setae with two strong, three posterodorsal setae. Tarsal claws long, subequal to combined length of fourth and fifth tarsomere. Abdomen: Elliptical, slightly pointed at apex. Median marginal setae and lateral marginal setae on all tergites, row of marginal setae on tergites 4 and 5. Abdomen 1.8–1.95 times as long as wide, 1.1–1.25 times as long as thorax in dorsal view. Sternites completely overlapped by tergites. Sternite 5 plate-like, posterior margin slightly invaginated. Terminalia: The single male was not dissected. Female (Figs. 2C–D, 3A–C): Differs from male as follows. Head with only strong silver pruinosity and dichoptic. Ocellar setae stronger. Frontal setae stronger, with 6–7 setae, the posterior lateroclinate. Two proclinate fronto-orbital setae. Inner and outer verticals stronger, the latter directed laterally. Prementum slightly shorter. Thorax with stronger silver pruinosity; in presutural scutum sometimes delimiting two diverging median black stripes and two large lateral black spots. Three katepisternal setae. Wing slightly shorter, ratio of wing length/maximum wing width 2.6 to 2.7. Calypters slightly shorter. Fore tibia with three anterodorsal and one posteroventral setae. Mid tibia with four anterior setae. Tarsal claws shorter and more curved, pulvilli shorter. Abdomen with silver pruinosity band stronger on tergite 3, weak on tergite 4. Tergite 5 anterior part telescopically inserted in abdomen. Fig. 3. Leucostoma acirostre in Bidens pilosa in São Paulo, SP, Brazil (photos taken between November and December 2021). A, Female ovipositing in the base of a capitulum in the process of fruiting. B, Female in a bud with developing achenes. C, Female in a bud with developed achenes. D, Male in in a bud with developing achenes. page 5 of 13 Zoological Studies 63:54 (2024) © 2024 Academia Sinica, Taiwan Terminalia (Fig. 4A): Terminalia. Sternite 5 plate-like. Tergite 6 strongly modified as two pincer structures; each posterior projection conical, without strong setae modified as spines, ending in 3 to 4 small projections; not fused dorsally; not fused to sternite 6. Sternite 6 subquadrate, not posteriorly invaginated. Tergite 7 divided in two separated pieces, with anterior elongation, and with a setulose lobe posteriorly. Sternite 7 as an elongated plate, with two short anterior projections; posterior margin deeply invaginated medially, forming two elongated lobes with setulae. Segment 8 fused; with a narrow-fused arch dorsally (probably part of tergite 8); ventral part elongated anteriorly, with a posterior bent piercer, projecting dorsally, then curving downwards (sternite 8). Epiproct and hypoproct not recognizable. Cerci elongate and thin, setulose posteriorly. Three spherical spermathecae. Puparium (Fig. 5A): Elliptical, without horns or conspicuous spines. Posterior spiracle at the end of conical tubercle, with two very sinuous spiracle openings. Distribution: U.S.A. (O’Hara et al. 2020); Brazil new record. Examined material: USA. Holotype, ♂, Texas, Brownsville, iv.1929, Townsend col (NMNH). BRASIL: 5♂, 4♀, Pernambuco, Petrolina, UNIVASF (CCA), 22.xi.2020, Martins, H.O.F. col (MZSP); 1♀, Mato Grosso do Sul, Cassilândia, Vinícius Souza, 3.ii.2022, (https://www.inaturalist.org/observations/106111066, photographic record, accessed on 12th July, 2024); São Paulo, São Paulo, Santo Amaro, R. Dios col. 1♀ (MZSP), exit host: 30.i.2024, emerged from puparium: 9.ii.2024, host: Harmostes parafraterculus; 1♂ (MZSP), 10.ii.2024; 1♀ (MZSP), 30.xii.2023. Fig. 4. Female terminalia, scale bar = 0.25mm, color legends on illustration. A, Leucostoma acirostre, ventral view. B, L. acirostre, lateral view. C, L. aterrimum, ventral view. D, L. aterrimum, lateral view. page 6 of 13Zoological Studies 63:54 (2024) © 2024 Academia Sinica, Taiwan Host list Hemiptera (Heteroptera), Coreidae Harmostes reflexulus (Say) (Arnaud, 1978) Hemiptera (Heteroptera), Rhopalidae Harmostes parafraterculus Göllner-Scheiding new record Leucostoma aterrimum (Villers, 1789) Musca aterrima Villers, 1789: 548. Leucostoma neomexicana Townsend, 1892: 169. Cyclodionaea acuminata Townsend, 1915: 234. Diagnosis: Females are easily distinguished from other Leucostoma by their long and slender abdomen, tapering distally (Fig. 6). All abdominal segments are similar in length/width ratio, however, the fourth tergite is telescopically retracted and seems wider (the retracted anterior portion lacks strong setulae). The males resemble L. simplex, according to Reinhard (1956), but the abdomen has pruinosities on the last two segments and is narrowed distally, not as much in females. Other characteristics are used in Reinhard’s identification key. The male terminalia (Fig. 4) likely has some features that will distinguish them from other Leucostoma species, but we lack material and illustrations to compare. Redescription: Male (Fig. 6A–B). Body length 4.6–5.5 mm. Coloration: Head brown to black with strong silver pruinosity; frontal vitta black. Scape and pedicel brown, first flagellomere black, brown basally; arista brown. Palpus pale tawny and prementum brown. Thorax black to brown with weak silver pruinosity dorsally and laterally. Thoracic spiracles brown. Wing hyaline, veins at base pale yellow. Calypters white. Halter pale brown. Legs dark brown to black; claws black; pulvilli pale tawny. Abdomen dark brown to black, tergites 4 to 5 fully covered with silver pruinosity. Head: Holoptic. Eye bare. Frontal vitta narrow, slightly narrower than fronto-orbital plate maximum width. Ocellar setae hairlike, lateroclinate. Eight to 11 frontal setae, hairlike, descending to pedicel level. Fronto orbital plate and dorsal part of parafacialia covered with setulae. Inner and outer vertical setae not differentiated from surrounding postocular setae. Postocellar setae hair-like. Antenna inserted at middle level of eye, short, not extending to vibrissa level. Lunule setulose. Scape short, about one-quarter length of pedicel. Pedicel setose dorsally, with 1 strong seta. First flagellomere slightly longer than pedicel, elliptical but broader distally. Arista micropubescent. Vibrissa strong, 4–5 subvibrissal setae. Eye about 0.8 to 0.9 head height. Gena about 0.1 eye height. Antennal axis slightly subequal to oral axis. Lower facial margin slightly protruding. Palpus slightly clavate. Prementum short, about half eye height. Labella well-developed, as long as first flagellomere. Thorax: Prosternum bare. Proepisternum bare. One strong proepimeral seta, surrounded with weaker setae. Anterior spiracle with both lappets welldeveloped, covering almost entire opening. Posterior spiracle with posterior lappet slightly larger than anterior. Acrostichal setae 1+1, with another presutural long setula. Dorsocentral setae 2+3. Intra-alar setae 1+2. Supra-alar setae 1+3, the first and third postsutural short. Postpronotal lobe with 3 setae, and 2 anterior long setulae. One postalar seta. Scutellum with one basal, one lateral, and one decussate apical pairs of setae. Two katepisternal setae, with posterior seta longer. One anterior and five posterior anepisternal setae. One anepimeron seta. Katatergite and anatergite Fig. 5. Puparium, posterior view. A, Leucostoma acirostre. B, Leucostoma aterrimum. page 7 of 13Zoological Studies 63:54 (2024) © 2024 Academia Sinica, Taiwan bare. Wing: subequal to thorax + abdomen length. Ratio of wing length/maximum wing width 2.3–2.6. Costal spine not differentiated. Costal vein without breaks, beyond intersection with Sc vein without ventral setulae. Cell r4+5 with long petiole, petiole more than three times r-m length, ending before wing apex. Base of vein R4+5 with 1 dorsal and ventral setae. Crossvein dm-cu slightly curved. Calypters rounded, large, reaching end of syntergite 1+2. Legs: Fore coxa with many anterodorsal setae. Fore femur with row of posterodorsal and posteroventral seta. Fore tibia with one posteroventral seta. Mid coxa with row of setae on anterior surface. Mid femur with rows of anteroventral and posteroventral setae on basal half, two posterodorsal preapical setae. Mid tibia with three anterior, two posterodorsal and two ventral setae. Hind coxa with row of anterodorsal setae. Hind femur with rows of anterodorsal, anteroventral and posteroventral setae on basal half, two anteroventral preapical setae. Hind tibia with three to four anteroventral setae, row of anterodorsal short setae with two strong, three to two posterodorsal setae. Tarsal claws longer than fifth tarsomere. Abdomen: Elliptical, slightly pointed at apex. Abdomen fully covered with long setulae. Median marginal setae and lateral marginal setae on all tergites, row of marginal setae on tergite 4 and 5. Abdomen 1.5–1.7 times as long as wide, 1.1–1.2 times as long as thorax in dorsal view. Sternites partially covered by tergites. Sternite 5 plate-like, posterior margin slightly invaginated. Terminalia (Fig. 7B): Tergite 6 partially fused to syntergosternite 7+8. Sternite 6 symmetric, V-shaped, connected by a membrane with tergite 6 and syntergosternite 7+8 on both sides. Epandrium arched, with setae; epandrium anterior process narrow. Bacilliform sclerite thin, elongate. Hypandrium with hypandrial apodeme slightly concave, with rounded apex in ventral view; hypandrial arms not fused dorsally; hypandrial central plate extended posteriorly, Fig. 6. Leucostoma aterrimum. A, Male, dorsal view. B, Male, lateral view. C, Female, dorsal view. D, Female, lateral view. Male from Andes, SP, Brazil, Female from São Paulo, SP, Brazil. page 8 of 13Zoological Studies 63:54 (2024) © 2024 Academia Sinica, Taiwan ending as two elongated pointed arms. Pregonite small, hard to differentiate, fused with hypandrium and postgonite; with sensory pits. Postgonite short and elongated, pointed apically. Phallapodeme rodlike, slightly enlarged in both ends, subequal to hypandrium length. Phallic guide not distinguished. Ejaculatory apodeme small, rod-shaped. Epiphallus not differentiated. Basiphallus as curved tube, with two anterior dorsal projections, fused with distiphallus. Distiphallus as a flattened ribbon, short. Syncercus fused, elongated, and pointed distally, the tip directed anteriorly in lateral view. Surstylus triangular, short. Female: Differs from male as follows. Head with only strong silver pruinosity and dichoptic. Ocellar setae stronger. Frontal setae stronger, with 5–7 setae, the posterior lateroclinate. Two proclinate frontoorbital setae. Inner and outer verticals stronger, the latter directed laterally. Thorax with stronger silver pruinosity; in presutural scutum delimiting two diverging median black stripes and two triangular lateral black spots. Three katepisternal setae. Calypters slightly shorter. Fore tibia with three anterodorsal and one posteroventral. Mid tibia with four anterior setae. Tarsal claws shorter and more curved, pulvilli shorter. Abdomen with silver pruinosity band stronger on tergite 3, weak on tergite 4. Abdomen longer and narrower, tapering gradually from base to apex; abdomen 2.3–2.5 times as long as wide, 1.5–1.7 times as long as thorax in dorsal view. Tergite 5 anterior part telescopically inserted in abdomen. Terminalia (Fig. 4B): Sternite 5 plate-like. Tergite 6 strongly modified as two pincer structures; each posterior projection elongated, with setae modified as spines; not fused dorsally; not fused to sternite 6. Sternite 6 subquadrate, posteriorly deeply invaginated. Tergite 7 divided in two separated pieces, with anterior elongation, and with a setulose lobe posteriorly. Sternite 7 as an elongated plate, with two anterior projections; Fig. 7. Leucostoma aterrimum, male terminalia, scale bar = 0.1 mm. A, Epandrium, cercus and surstylus, posterior view, setulae represented only on the left side, B, Epandrium, cercus, surstylus and bacilliform sclerite, lateral view, C, Sternites 5 and 6, ventral view, setulae represented only on the left side, D, Lateral view, highlighting outer and inner structures (dashed lines). Abbreviations: B scl = bacilliform sclerite, bas = basiphallus, e = epandrium, c = syncercus, dist = distiphallus, ej ap = ejaculatory apodeme, hyp = hypandrium, post = postgonite, phapod = phallapodeme, pre = pregonite, s = surtylus, st = sternite. page 9 of 13Zoological Studies 63:54 (2024)