Dixella woodi Chaverri & Borkent, 2007 (Diptera, Dixidae): Description of the female and a new record from Peru

ABSTRACT

This study provides a description of the female and a redescription of the male terminalia of Dixella woodi Chaverri & Borkent, 2007, which is recorded in Peru for the first time. Diagnoses for the other two Peruvian Dixidae species, Dixella andeana (Lane, 1942) and Dixella peruviana (Edwards, 1931), and remarks on their types are presented along with a key to distinguish the three species. Dixella woodi differs significantly from other Neotropical Dixella Dyar & Shannon, 1924 species, such as the presence of elongated setae on the medial portion of the katepisternum and unique characteristics in both male and female terminalia. The findings underscore the importance of systematic collection sampling and taxonomic revision in the Neotropical region to advance our understanding of Dixidae diversity and distribution.

Keywords:
Meniscus midges; Taxonomy; Neotropical region; South America

Introduction

Dixidae is a low-diversity family of Diptera, with approximately 200 extant species in eight genera (Wagner et al., 2008; Greenwalt & Moulton, 2016). Dixella Dyar & Shannon, 1924 is the second most diverse genus of the family and is widely distributed worldwide, although the distribution is not uniform. Adults of meniscus midges can be found around oviposition sites where the immatures will develop, such as streams, lakes, swamps, and phytotelmata (Corrêa & Gil-Azevedo, 2018). Active search for immatures (with trays, sieves, and pipettes) and adults (with hand-net and aspirator), as well as interception and attraction traps, such as malaise, CDC, and white light, are effective for capturing the adults (Corrêa & Gil-Azevedo, 2018). The immatures can be collected and reared to obtain the adults.

Three genera are recorded in the Neotropical region: Dixella (31 species), Mesodixa Belkin, Heinemann & Page, 1970 (1 species), and Nothodixa Edwards, 1930 (4 species). Mesodixa was recorded from Jamaica and Hispaniola (Belkin et al., 1970; Belkin & Heinemann, 1972) and Nothodixa from Chile and Argentina (Lane, 1953). In contrast, the 31 species of Dixella are widely found in the Neotropical region, from Mexico to Argentina (Stone, 1966; Belkin et al., 1970; Peters, 1980; Chaverri & Borkent, 2007; Huerta & Ibáñez-Bernal, 2021, 2023; Corrêa et al., 2024).

Only two species are recorded from Peru: Dixella andeana (Lane, 1942) in Iquitos, and Dixella peruviana (Edwards, 1931) in Lima (Edwards, 1931; Lane, 1942). In this study, we present a new record from Cusco of Dixella woodi Chaverri & Borkent, 2007, based on two specimens, male and female, collected from the same locality. The somatic features of both are very similar allowing us the association between them, as usual in Dixidae. We describe the female, and provide comments on the male terminalia, based on our material. We also present photos and information about the type material of the other two species, D. andeana and D. peruviana, described from Peru.

Material and methods

Dixella woodi was collected by Aida Vanessa Gómez Falcón (MNRJ) and Karen Roa Castro (MUSM) via hand net in Machu Picchu, Urubamba, Cusco, Peru, on May 22, 2021 (Figs. 1G-H, 6A-C). The specimens were initially fixed in 96% ethanol and later mounted on microscope slides using Euparal (Upton & Mantle, 2010) and deposited in the Entomological Collection of Museu Nacional, Universidade Federal do Rio de Janeiro (MNRJ). Terminology follows Chaverri & Borkent (2007) and Cumming & Wood (2017). Photos of D. woodi were captured using a Leica M205C stereoscopic microscope equipped with a FusionOptics digital camera, and drawings were made using a camera lucida. Images and illustrations of D. woodi were edited and vectorized using Adobe Illustrator CC. Maps were created using SimpleMappr (Shorthouse, 2010).

Figure 1
Dixella woodi Chaverri & Borkent, 2007, female. A. Habitus (lateral view); B. Head; C. Antenna; D. Abdomen (ventral view); E. Wing; F. Thorax (lateral view); G. Slide and labels of male; H. Slide and labels of female. Scale bar: A = 1.8 mm; B = 0.4 mm; C, E = 0.6 mm; D, F = 0.5 mm.

Figure 2
Dixella woodi Chaverri & Borkent, 2007, female. A. Terminalia (ventral view); B. Sternite IX; C. Cercus and Segment X (lateral view). Scale bar: A = 0.2 mm; B-C = 0.06 mm. Abbreviations: cer = cercus; seg X = segment X.

Figure 3
Dixella woodi Chaverri & Borkent, 2007, male. A. Terminalia (ventral view); B. Tergite X (lateral view). Scale bar: A = 0.04 mm; B = 0.05 mm. Abbreviations: ap lob = apical gonocoxal lobe; gon ap = gonocoxal apodeme; goncx = gonocoxite; gonst = gonostylus; par = paramere.

Figure 4
Dixella andeana (Lane, 1942), male (HOLOTYPE). A. Habitus (lateral view); B. Thorax (lateral view); C. Thorax (dorsal view); D. Labels (NHM photos).

Figure 5
Dixella peruviana (Edwards, 1931), male (HOLOTYPE). A. Habitus (lateral view); B. Habitus (dorsal view); C. Abdomen (ventral view); D. Labels. Scale bar: A-B = 1 mm; C = 0.2 mm (NHM photos).

Figure 6
A-C. Collection site in PERU, Cusco, Urubamba, Machu Picchu, Quebrada Chachabamba.

Results

Dixella woodi Chaverri & Borkent, 2007 (Figs. 1-3)

Diagnosis. Adult. Only species of Dixella in Neotropical Region with katepisternum having patch of elongated setae on medial portion. Female: Sternite IX with medial portion tapered and slender (V-shaped) with undulating sides, lateral portion anteriorly wider, featuring ventral and laterally tapered projections. Segment X very elongated, extending beyond the apical portion of the cercus. Male: Gonocoxite with apical lobe with expanded apical portion with three subbasal setae (two in posterior portion and one in anterior portion) and one elongate basal seta.

Description of Female. (Figs. 1–2). Body length: 4 mm (n= 1). Head (Figs. 1B-C) dark brown with setae around the eyes in the posterior portion. Scape collar-like. Pedicel globose, 0.45x length of flagellomere I. Flagellum light brown with 14 flagellomeres. Flagellomere I slightly cylindrical, 1.5x length of flagellomere II. Flagellomere XIV with pair of divergent apical setae. Clypeus brown, subquadrate, with ca. 15 setae in the medial portion. Maxillary palp I-III ratio (1, 1.5, 3.5), missing the IV-V. Thorax (Fig. 1F). Scutum light brown with three brown stripes: one medial extending from anterior to middle portion as longitudinal slender strip; two brown longitudinal lateral stripes extending from prescutal to prescutellar area (dorsal view). Acrostichal and dorsocentral setae complete; antealar area with ca. 15 scattered setae. Antepronotum setose subtly darker than postpronotum. Postpronotum brown with five setae. Anterior and posterior anepisternum brown. Katepisternum with dorsal portion brown and ventral portion light brown, medial portion with ca. 10 setae, and postero-medial portion lighter than anterior portion. Anepimeron light brown with dorsal portion brown and antero-ventral margin lighter than medial portion. Metanepisternum and meron brown. Scutellum brown and setose without a delimitated row of setae. Mediotergite brown. Legs (Fig. 1A) uniformly brown with lengths of (n= 1): fore leg [femur (1.8 mm), tibia (1.8 mm), tarsus (2.8 mm)], mid leg [femur (2.2 mm), tibia (2.1 mm), tarsus (3 mm)], and hind leg [femur (1.9 mm), tibia (2.3 mm), tarsus (3.3 mm)]. Fore and hind coxae slightly lighter than mid coxa; Coxae with setae anterolaterally. Tibiae with apical spur, hind tibia spur curved and twice as long as fore and mid tibiae spurs. Hind tibia strongly swollen apically with distinct patch of setae. Claws non-pectinate with basal combs. Basal comb of claws with two ventral tines. Wing (Fig. 1E) (n= 1; length: 3.9 mm; width: 1.3 mm) with membrane hyaline. Wing veins brown and setose. Vein Sc ends basally to Rs origin. Vein R₂₊₃ curved, branched and with the origin subtly apical to crossvein r-m origin. Vein M₁₊₂ bifurcated; M bifurcation ends apical to R₂₊₃ branch origin. Crossvein m-m weak and near to the crossvein r-m terminus. False vein distinct and parallel to CuA, reaching ca. the basal 2/3 of CuA. Vein CuP ends apical to Rs origin. Length ratios R₂₊₃/R₃ = 0.35, M₁₊₂/M₂ = 1. Halter brown with light brown base. Abdomen (Fig. 1D): uniformly light brown. Terminalia (Figs. 2A-C): Spermatheca rounded and brown. Sternite VIII light brown, elongate (1.6x longer than wider), posterior portion dark brown with elongate setae, and concave. Tergite IX brown with posterior margin setose. Sternite IX light brown, single piece, medial portion tapered and slender (V-shaped) with undulating sides, lateral portion with anterior portion wider. Segment X dark brown, single piece, very elongate (extending beyond apical portion of cercus), lateral margin with many elongate setae, and medial cleft projecting to subapical portion (junction point between the parts). Cercus dark brown, elongate, apical portion rounded with elongate setae.

Male redescription. (Figs. 3A-B). Terminalia: Tergite X with distinct lateral projection extending from basal portion of central plate (dorsal view) to sides. Parameres L-shaped (lateral view) and projecting laterally. Aedeagus like a stripe reaching approximately medial portion of base of gonocoxite (dorsal view) and with median projection extending anteriorly, featuring small invagination; lateral portion with slight expansion at base. Gonocoxal apodeme tapered, projecting anteriorly, and curving towards medial portion. This redescription of the male terminalia is meant to be complementary to the original description (Chaverri & Borkent, 2007). For somatic structures, refer to the original description.

Material. 1♂ (MNRJ#41280) and 1♀ (MNRJ#41515) in slides. Peru, Cusco, Urubamba, Machu Picchu, Quebrada Chachabamba, S13°11’18.8” W72°30’38”, 2240 m, 22/V/2021, hand net, AVG Falcón & KRM Castro col. (Figs. 1G-H).

Distribution. COSTA RICA, San José, Escazú, San Antonio (type-locality); Tarrazú, San Carlos. PERU, Cusco, Urubamba (new record) (Fig. 7).

Figure 7
Distribution map of Dixidae species recorded from Peru.

Remarks. Dixella woodi was described based on two adult male specimens. This species differs significantly from other species recorded from Costa Rica due to characteristics of the katepisternum and male terminalia (Chaverri & Borkent, 2007). The presence of setae on the katepisternum is a unique feature among neotropical species of Dixella. The shape and arrangement of setae of the gonocoxite of D. woodi distinguishes it from other Dixella species (Chaverri & Borkent, 2007), which typically have an apical lobe with an expanded apex, as seen in D. maculata Chaverri & Borkent, 2007, D. hernandezi Chaverri & Borkent, 2007, and D. suzukii Chaverri & Borkent, 2007. Dixella maculata has a wing with a brown spot over the crossvein r-m and an apical lobe with two apical setae. Dixella hernandezi has numerous small spicules and a bilobed apex of the apical lobe. Dixella suzukii has two elongated setae at the base of the apical lobe, and the base of the gonostylus is widened, tapering towards the apex.

The female of D. woodi is very distinct from the other females of Dixella species recorded for the Neotropical region. Few species of Dixidae have females known and/or described in detail, especially in the Neotropical region. Only 11 species have females described in detail that assists for comparison, namely: Dixella atitla Huerta & Ibáñez-Bernal, 2021, Dixella lobata Chaverri & Borkent, 2007, Dixella machiotla Huerta & Ibáñez-Bernal, 2023, D. maculata, Dixella moultoni Corrêa, Scarpa, Pinho & Gil-Azevedo, 2024, Dixella scitula Belkin, Heinemann & Page, 1970, Dixella shannoni (Lane, 1942), Dixella spinosa Corrêa, Scarpa, Pinho & Gil-Azevedo, 2024, D. suzukii, Dixella venezuelensis (Lane, 1942), and Mesodixa biambulacra Belkin, Heinemann & Page, 1970 (Lane, 1942, 1953; Belkin et al., 1970; Chaverri & Borkent, 2007; Huerta & Ibáñez-Bernal, 2021, 2023; Corrêa et al., 2024). The female of D. woodi can be distinguished from the other species (mentioned above) by the length of segment X, which extends beyond the apical portion of the cercus, while the other species has the length of segment X equal or shorter than the length of the cercus.

Chaverri & Borkent (2007) warned about one female specimen collected in Colombia (Cundinamarca, Finca Bella Vista) that could be a female of D. woodi, but due to that distance from the type locality (Costa Rica), they preferred not to designate it as the female of D. woodi. We believe that this material could be a female of D. woodi, but we did not observe it in this study.

Chaverri & Borkent (2007) described the male of D. woodi and made the following comment: “Parameres, aedeagus not identified with certainty”. Some structures of the male terminalia can be challenging to visualize when fixed on slides. We described and redescribed some of these structures that were not clearly visualized, and emphasized others that were observed in the analyzed specimen, such as paramere, aedeagus, tergite X, and gonocoxal apodeme. The remaining structures in the description of D. woodi by Chaverri & Borkent (2007) are as described in the original description.

Key to adult Dixidae from Peru

1. Katepisternum with elongate setae …............................................... Dixella woodi

- Katepisternum without setae ……….…………………………………..…….…. 2

2. Wing vein R₂₊₃ bifurcation origin basal relative to M₁₊₂ bifurcation origin; Legs brownish …................................................................................ Dixella peruviana

- Wing vein R₂₊₃ bifurcation origin apical relative to M₁₊₂ bifurcation origin; Legs yellowish ……….……………………………………..…….…. Dixella andeana

Below, we give some remarks on the other two species of Dixidae which have been found in Peru.

Dixella andeana (Lane, 1942) (Figs. 4A-D)

Diagnosis. Adults has wing vein R₂₊₃ bifurcation origin apical relative to M₁₊₂ bifurcation origin; vein R₂₊₃ origin very apical to crossvein r-m origin; thorax (lateral view) with two parallel brown stripes.

Type Material. ♂ HOLOTYPE (pinned, NHM#013444278): PERU, Loreto, Iquitos

Distribution. This species is recorded only from type locality: PERU, Loreto, Iquitos (Fig. 7).

Remarks. Dixella andeana has the thorax with two parallel brown stripes, like D. peruviana and D. shannoni. They can be differentiated through wing venation: D. shannoni has the vein R₂₊₃ bifurcation origin relatively near to the M₁₊₂ bifurcation origin, while D. peruviana has the vein R₂₊₃ bifurcation origin basal relative to the M₁₊₂ bifurcation origin. Male terminalia also serve to distinguish these three species: D. peruviana has a thin and elongated gonostylus, while D. andeana has a short, wide, gonostylus strongly hirsute along outer margin; D. shannoni has apical lobe with two subbasal setae, while that of D. andeana has four apical setae (Lane, 1942, 1953; Chaverri & Borkent, 2007; Huerta & Ibáñez-Bernal, 2021).

Despite Lane (1942) naming this species with the epithet ‘andeana’, the type locality is in the Amazon Rainforest (Fig. 7), an area characterized by low altitude and dense forest vegetation contrasting significantly with the high-altitude and different flora of the Andean Mountain Range.

Dixella peruviana(Edwards, 1931) (Figs. 5A-D)

Diagnosis. Adults have wing vein R₂₊₃ bifurcation origin relatively basal to M₁₊₂ bifurcation origin; vein R₂₊₃ origin apical to crossvein r-m origin; thorax (lateral view) with two parallel brown stripes.

Type Material. ♂ HOLOTYPE: (pinned, with abdomen on slide, NHM#010864741): Lima, Lima, Verrugas.

Distribution. This species is recorded only from type locality: PERU, Lima, Lima, Verrugas (Fig. 7).

Remarks. Dixella peruviana has thorax with two parallel brown stripes, like D. andeana and D. shannoni. They can be differentiated through wing venation and male terminalia (see D. andeana remarks).

Discussion

The female terminalia can be very useful for characterizing and differentiating Dixidae females. The sternite IX of Dixella species is very informative when comparing between species. For example, it can be found as a single piece, subdivided, and/or possess projections of varying form. The cercus and segment X can also be informative, especially the relative sizes between them and the arrangement of elongated setae (when present).

Dixella trinitensis (Lane, 1943), D. venezuelensis, and D. woodi are species with a wide distribution range in Central America and South America. In fact, we know very little about the distribution of the family in the Neotropical Region and this wide distribution range probably will be observed in other species as our knowledge advances, especially in the Amazon rainforest. The three species now recorded in Peru were found through nonsystematic sampling restricted to the type localities (D. andenana and D. peruviana) or single records (D. woodi). The surrounding countries also show specific records of Dixidae species, Venezuela with D. venezuelensis, or no records, as Bolivia, Colombia, and Ecuador. Brazil has nine recorded species, but none in the Amazon Region.

The lack of systematic collection sampling and taxonomic revision of Dixidae species, especially in the Neotropical Region, hinders the resolution of the actual diversity and distribution of the family.

Acknowledgments

We thank Aida Vanessa Gómez Falcón (MNRJ) and Karen Roa Castro (MUSM) for collecting the material of D. woodi from Peru, and Servicio Nacional de Áreas Naturales Protegidas por el Estado (Resolución Directoral N° 028-2021-SERNANP-DGANP) for the license and help during the collections, especially the park rangers Aldo Ander Huamani Taco, Marcel Ramos Quispe, Ronald Surco Ramos, and Danilo Quispe Rodriguez. Also, thanks to Dr. Duncan Sivell (The Natural History Museum) for providing the photos of the holotypes of D. andeana and D. peruviana. We thank John K. Moulton (UTK) and André P. Amaral (University of Munich) for the review and valuable suggestions throughout the manuscript. CCDC thanks to Pós-graduação em Zoologia (UFRJ) for the doctoral scholarships and grants. CCDC - National Council for Scientific and Technological Development - CNPq (142460/2019-2), and Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro - FAPERJ (201.657/2021) for the scholarships. LHGA - CNPq research fellowship (316810/2021-5) and FAPERJ (E-26/200.083/2019, Apoio Emergencial ao Museu Nacional), and by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES, Programa PROEX).

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Edited by

Associate Editor: Fabio Quinteiro

Publication Dates

• Publication in this collection
  19 Aug 2024
• Date of issue
  2024

History

• Received
  09 Apr 2024
• Accepted
  06 July 2024