Taxonomic revision of the New World genus Chlorotabanus Lutz, 1913 (Diptera: Tabanidae) Author Krolow, Tiago Kütter Author Henriques, Augusto Loureiro text Zootaxa 2010 2656 1 40 journal article 10.5281/zenodo.276219 f7dbab6f-314a-405f-be39-e2ea55535a41 1175-5326 276219 Chlorotabanus mexicanus ( Linnaeus, 1758 ) ( Figure 9 A–J) Tabanus mexicanus Linnaeus, 1758 : 602 ; Knab, 1916 : 96 –97 (redescription and fig.1); Bequaert, 1926 : 234 (key); Philip, 1952 : 310 –311 (synonymous T. olivaceus De Geer ). Tabanus (Chlorotabanus) mexicanus , Kröber, 1930 : 15 , 18 (key and diagnosis); 1934: 297 (catalog); Bequaert, 1940 : 449 (citation); 1944: 17 (citation). Chlorotabanus mexicanus , Kröber, 1930 : 18 ; 1931: 91; Fairchild, 1940 : 714 –716 (key, redescription and figs.); Stone, 1944 : 132 (citation). Bequaert & Renjifo-Salcedo, 1946 : 73 (distribution); Fairchild, 1953 : 44 (citation); Fairchild, 1969 : 208 (classification); 1971: 55 (catalog); Goodwin & Murdoch, 1974 : 99 –102 figs. (pupa, larva); Henriques & Gorayeb, 1993 : 9 (MPEG collection); Fairchild & Burger, 1994 : 87 (catalog); Henriques, 1995 : 69 (INPA collection); Krolow & Henriques, 2008 : 269 (citation); Coscarón & Papavero, 2009b : 68 (catalog); Krolow & Henriques, 2009 : 209 (citation). Chlorotabanus (Chlorotabanus) mexicanus , Philip & Fairchild, 1956 : 315 –316, fig. 1F (review). Tabanus olivaceus DeGeer, 1776 : 229 ; Philip, 1952 : 311 (redescription and synonymy). Tabanus punctatus Fabricius, 1787 : 355 . Type locality: South America . Diagnosis: Medium sized ( 12.1 mm ), thorax grayish-white with yellowish pilosity. Abdomen greenishyellow with yellow pilosity. Frons with slight convergence at the base. Hyaline wing, except the yellowish costal cell and the dark spots at the intersections of the veins and usually at the apex of some veins. Redescription ( Ψ ) : Body length 10.2–14.2 mm (X = 12.1 mm , N = 20) ( Fig. 9 A–B); wing length 9.0– 12.4 mm (X = 10.8 mm , N = 20); wing width 2.6–4.1 mm (X = 3.4 mm , N = 20). Head ( Fig. 9 C): Eyes vary from grayish-bronze to reddish-brown. Frons variable, in general, elongate and convergent at base, while occasionally frons may be wider, almost parallel, with a slight convergence at the base, F.I. 5.2–6.7 (X = 5.8, N = 20), D.I. 1.3–1.6 (X = 1.4, N =20), yellowish-brown pruinosity and yellow pilosity. Subcallus, parafacialia, gena and face with pruinosity as frons. Parafacialia, gena and face with dense yellow hairs, while the subcallus has few hairs and a naked central region. Palpus yellowish-brown with yellow hairs. Proboscis with theca that varies from dark yellow to greenish; labella dark-green to black. Antenna ( Fig. 9 D) variable in shape and color, flagellum with basal plate that forms an acutely angled dorsal elevation B.P.I. 1.3–1.7 (X = 1.4, N = 18), about 1.5–2.0x stylus length Flg.I. 1.3–1.6 (X = 1.4, N = 17). Thorax: Scutum with orangish-brown integument, often with a greenish or yellowish spot in the middle of the posterior region near the pre-scutellum, covered with grayish-white pruinosity and with yellow hairs. In dorsal and postero-dorsal views, the spot in the middle is visible in some specimens, apparently without pruinosity in that region. However, in antero-dorsal view, the pruinosity is visible covering the spot. This pattern of angle and pruinosity is also found in the scutellum. This phenomenon occurs due to the incidence angle of the light and the orientation of the pilosity and by turning the specimen under the stereomicroscope one may see the pilosity appear and disappear depending upon the angle. Slender legs, yellowish or greenish with yellow hairs, except for the dense black hairs on the distal ¼ of the tibiae and the dorsal ¼ of the fourth and fifth tarsomeres. Hyaline wing ( Fig. 9 E), except for the yellowish basal costal and costal cells and the small dark spots on the transverse veins, at the base of the medial basilar and radial basilar cells, at the apex of veins R2+3, R4, R5, M1, M2, M3, CuA1 and A1+CuA2, on the anterior 1/3 of vein M3 and the alular incision. One commonly seen variation is the lack of or lightening of the spots on veins M1, M2, M3, CuA1 ( Fig. 9 J). Pterostigma yellowish or greenish. Fork of the vein R4+5 is square, with a poorly or well-developed appendix. FIGURE 9. Chlorotabanus mexicanus (A–E, J Ψ; F–I ♂): A–B, F–G, Body (dorsal and lateral views); C and H, Head (frontal view); D and I, Antenna (lateral view); E and J, Wing (dorsal view). Abdomen: Yellowish or greenish, covered by yellow pilosity, except at tergites 6 and 7 with few black hairs. Variations: see redescription. Male : Body length 10.3–13.2 mm (X = 12.0 mm, N = 20) ( Fig. 9 F–G); wing length 8.6–10.3 mm (X = 9.6 mm , N = 20); wing width 2.8–3.4 mm (X = 3.1 mm , N = 20). Similar to the female, except for the following: holoptic eyes ( Fig. 9 H), where largest ommatidia occupy the upper 2/3 and the smallest ommatidia the lower 1/3. Ocellar tubercle absent, vertex depressed. Palpus porrect, yellowish or greenish with yellow hairs. Antennae ( Fig. 9 I) with stylus subequal to length of basal plate, B.P.I. 1.2–1.5 (X = 1.3, N = 19), Flg.I. 1.0–1.1 (X = 1.05, N = 19). Distribution: Mexico , Belize , Honduras , Nicaragua , Costa Rica , Panama , Colombia , Venezuela , Trinidad and Tobago , Suriname , French Guiana , Brazil (Pará), Ecuador . Holotype Ψ: at the?Naturhistoriska Riksmuseet - Stockholm (not examined, see Discussion below). The synonym T. punctatus ( Holotype Ψ) was examined and was in very poor condition, with only part of the thorax and the two wings. Also, photos of T. olivaceus ( Holotype Ψ) were used, sent by Dr. Bert Gustafsson ( NHRS ). Type-material examined: “ Tabanus \ punctatus \ Fabricius, 1787 \ Man .Ins.II\ 1787:355” “Coll. Fabricius” ( Holotype Ψ ZMUC ). Additional material examined . MEXICO . Quintana Roo , Tabí, 12.viii.1925 (Alfonso Dampf Colln Press to CAS by Cornelius B. Philip), 1Ψ, Chlorotabanus mexicanus L. ( sic. ) det. Kröber, 1929 ( CAS ); idem , Santa Cruz Chico, 25.viii.1925 (Alfonso Dampf Collection Press to CAS by Cornelius B. Philip), 1Ψ, Chlorotabanus mexicanus L. ( sic. ) det. Kröber, 1929 / Chlorotabanus mexicanus (Linne) det. C. B. Philip ( CAS ); [Campeche] , Icaíche (Blue Creek), 3–4.x.1925 (Alfonso Dampf Collection Press to CAS by Cornelius B. Philip), 1Ψ, Chlorotabanus mexicanus L. ( sic. ) det. Kröber, 1929 / Chlorotabanus mexicanus (Linne) det. C. B. Philip, [19]52 ( CAS ); Chiapas , Palenque, 10.ix.1974 (G. Bohart, W. Hanson), 1ɗ, Chlorotabanus mexicanus L. ( sic. ) det. G. B. Fairchild, 1976 ( UMNH ); BELIZE . Cayo , (Chiquibul Forest, Las Cuevas clearing, m v light sheet), ii.1996 (J. H. Martin), 2Ψ, (NHM); HONDURAS . (Benque Viejo, Father Stanton), undated (unknown), 1Ψ, T. (Chlorotabanus) mexicanus (L.) det. [G. B.] Fairchild, 1938 ( MZSP ); Rio Temos, vi.1937 (J. J. White), 1Ψ, Chlorotabanus mexicanus Linn. ( sic. ) det. J. E. Chainey, 1975 (NHM); Punta Gorda, vii.1935 (J. J. White), 1ɗ, Chlorotabanus mexicanus Linn. ( sic. ) det. J. E. Chainey, 1975 (NHM); NICARAGUA . (Cukra, Colina), 11.ii.1947 (Lewis E. Long), 1Ψ, Chlorotabanus mexicanus (Linn.) det. C. B. Philip, [19]66 ( FMNH ); COLOMBIA . [Valle del Cauca] : Buenaventura, 2.i. [19]13 (Spurrell), 1Ψ, C. mexicanus without det. (NHM); [Cundinamarca] : Bogotá, 1914 (A. Balfour),1Ψ, (NHM); idem , (environs of Bogotá, c.9000), iv.1914 (A. Balfour), 5Ψ, (NHM); Dept. Cauca , Guapi (Altitude 10M. Tropical Rain Forest, Flight trap/CO2), ??.10.[19]76 (R. Wilkerson), 1Ψ, Chlorotabanus mexicanus (Linn.) det. G. B. Fairchild, 1981 ( INPA ); [?] : San Juan R. Negreia, 2.xii. [19]13 (H. G. F. Spurrell), 2ɗ, (NHM); idem: Atrato Valley, vi.1914 (A. Balfour), 1Ψ, (NHM); VENEZUELA . Sucre : San Bonifacio, 10.iv. [19]64 (Ronderas), 1Ψ, Chlorotabanus mexicanus (L.) det. Coscarón, [19]74 ( INPA ); [Monagas] : (Caripito), 18.iv.1942 (unknown, Cornelius B. Philip Collection Donated to California Academy of Sciences), 1ɗ, Chlorotabanus mexicanus det. C. B. Philip [19]49 ( CAS ); idem, 26.iv.1942 (unknown, Cornelius B. Philip Collection Donated to California Academy of Sciences), 1Ψ, ( CAS ); COSTA RICA . [?] : Fulda, 1Ψ, Chlorotabanus mexicanus (L.) det. S. W. Bromley, 1949 (NHM); idem , Finca Suerre (from horse), 11.iii.28 (unknown, Cornelius B. Philip Collection Donated to California Academy of Sciences), Compared With Type Ψ T. punctatus Fabr. April 1951 – C. B. Philip Same ant.[ena] plate + front wing spots + intens. abd.[omen] Discoloration but type Thor.[ax] + legs discal, also, costal cell darken in type , Chlorotabanus mexicanus Linn. Ψ det. C. B. Philip [19]40, 1Ψ, ( CAS ); Guan.[acaste] : ( 3km SE R. Naranjo), xii.1991 (F. D. Parker), 1ɗ, ( UMNH ); idem , iv.1992 (F. D. Parker), 1Ψ, ( UMNH ); idem , 11–21.iv.1992 (F. D. Parker), 1Ψ, ( UMNH ); idem , 22–30.iv.1992 (F. D. Parker), 2Ψ, ( UMNH ); idem , v.1992 (F. D. Parker), 1Ψ, ( UMNH ); idem , 16– 3.v.1992 (F. D. Parker), 1Ψ, ( UMNH ); idem , 1–5.vi.1992 (F. D. Parker), 1Ψ, ( UMNH ); idem , 21–30.vi.1992 (F. D. Parker), 1Ψ, ( UMNH ); idem , 11–20.vii.1992 (F. D. Parker), 1Ψ ( UMNH ); idem , 21–28.xii.1992 (F. D. Parker), 2Ψ, ( UMNH ); idem , 10–23.vi.1993 (F. D. Parker), 1Ψ, ( UMNH ); idem , 14–16.vi.1993 (F. D. Parker), 1Ψ, ( UMNH ); idem , 23–29.vi.1993 (F. D. Parker), 1Ψ, ( UMNH ); idem , 1–15.viii.1993 (F. D. Parker), 1Ψ, ( UMNH ); idem , 16–31.viii.1993 (F. D. Parker), 1Ψ, ( UMNH ); idem , ( 14 km S Cañas), 11–31.i.1990 (F. D. Parker), 1Ψ, 1ɗ, ( UMNH ); idem , 1–11.ii.1990 (F. D. Parker), 1Ψ, ( UMNH ); idem , 15–24.ii.1990 (F. D. Parker), 5Ψ, 2ɗ, ( UMNH ); idem , 16–23. iv.1990 (F. D. Parker), 1ɗ, ( UMNH ); idem , 19.xi.1990 (F. D. Parker), 1Ψ, ( UMNH ); idem , 24–28.ii.1991 (F. D. Parker), 1Ψ, ( UMNH ); idem , 12.ii.– 16.iii.1991 (F. D. Parker), 2Ψ, ( UMNH ); idem , (S Cañas), 9–14.ii.1989 (F. D. Parker), 1Ψ, ( UMNH ); La Cruz ( 12km SE), i.1988 (A. Solis), 1ɗ, ( INBIO ); Nandayure, v.2004 (W. Porras), 1Ψ, ( INBIO ); Ala [juela] : Guatuso (P.N. Volcán Tenório, Laguna La Carmela), 18.vi.2007 (J. A. Azofeifa), 3Ψ, 4ɗ, ( INBIO ); idem, vi.2004 (J. A. Azofeifa), 2Ψ, ( INBIO ); Los Chiles (Laguna Medio Queso), 2.ix.2005 ( Y . Cardenas), 2Ψ, 1ɗ, ( INBIO ); Upala (Bijagua, Finca Inti-Aura), 27.iv.2009 (J. A. Azofeifa), 1ɗ, ( INBIO ); San Carlos (Pital, Boca Tapada), vi , xi.2004 (B. Hernández), 1Ψ, 2ɗ, ( INBIO ); ( 20km S Upala), vii.1990 (F. D. Parker), 1Ψ, ( UMNH ); idem , 11–20.iv.1991 (F. D. Parker), 1Ψ, ( UMNH ); idem , 10–29.v.1991 (F. D. Parker), 2Ψ, ( UMNH ); idem , 22– 31.v.1991 (F. D. Parker), 2Ψ, ( UMNH ); idem , 1–11.vi.1991 (F. D. Parker), 1ɗ, ( UMNH ); idem , 3.vi.1991 (F. D. Parker), 1Ψ, ( UMNH ); idem , 11–21.vi.1991 (F. D. Parker), 1Ψ, ( UMNH ); idem , 20.vii.1991 (F. D. Parker), 1Ψ, ( UMNH ); idem , 13.xii. [19] 90 – 9.i. [19]91 (F. D. Parker), 2Ψ, ( UMNH ); idem , ( 2km S Pital), 5–28.ix.1988 (F. D. Parker), 1Ψ, ( UMNH ); Her[edia] : Sarapiquí (Cecafor), 1–4.viii.2006 (J. A. Azofeifa), 1Ψ, 2ɗ, ( INBIO ); (La Selva Res. Sta), 11–17.vi.1986 (W. Hanson, G. Bohart), 3Ψ, 3ɗ, ( UMNH ); idem , same date (C. L. Clemons), 1Ψ, 1ɗ, ( UMNH ); idem , same date (C. L. Clemons), 1Ψ, Chlorotabanus mexicanus L. det. G. B. F.[airchild], 1986 ( UMNH ); idem , same date (D. J. Keller), 2Ψ, ( UMNH ); idem , 24–30.viii.1988 (W. Hanson), 1ɗ, ( UMNH ); Limón : Barra del Colorado, 19.viii.2004 (B. Gamboa, W. Porras, D. Briceno, M. Moraga, Y . Cardenas), 2ɗ, ( INBIO ); Valle La Estrela, v.2007 (J.A. Azofeifa, J. Montero), 1Ψ, ( INBIO ); (P.N. Tortuguero), 14–16.viii.2004 (B. Gamboa, W. Porras, D. Briceno, M. Moraga, Y . Cardenas), 1Ψ, ( INBIO ); (Hacienda Tapezco, 29 air km W Tortuguero, el. 40m , lat. 10°30’N ; long. 83º47’W ), 3.iii.1978 (C. L. Hogue), 1Ψ, Chlorotabanus mexicanus ( Linnaeus, 1758 ) det. J. F. Burger, 1995 ( LACM / 246733); idem , 21– 28.iii.1988 (W.E. Steiner, J.M. Hill, J.M. Swearingen, J.M. Mitchell), 1Ψ, ( USNM ); idem , 8.iii.1978 (J.P. Donahue, D. Panny, D. Moelller, C. Lewis, LACM /Earthwatch trees of Tapezco expedition), 1Ψ, ( LACM ENT / 246794); idem , 9.iii.1978 (J.P. Donahue, D. Panny, D. Moelller, C. Lewis, LACM /Earthwatch trees of Tapezco expedition), 1Ψ, ( LACM ENT / 246782); idem , 10.iii.1978 (J.P. Donahue, D. Panny, D. Moelller, C. Lewis, LACM /Earthwatch trees of Tapezco expedition), 1Ψ, 1ɗ, ( LACM ENT / 246791/ 246790); idem , 12.iii.1978 (J.P. Donahue, D. Panny, D. Moelller, C. Lewis, LACM /Earthwatch trees of Tapezco expedition), 2Ψ, 2ɗ, ( LACM ENT / 246783/ 246788/ 246778/ 246789); idem , 13.iii.1978 (J.P. Donahue, D. Panny, D. Moelller, C. Lewis, LACM /Earthwatch trees of Tapezco expedition), 2ɗ, ( LACM ENT / 246793/ 246795); idem , 14.iii.1978 (J.P. Donahue, D. Panny, D. Moelller, C. Lewis, LACM /Earthwatch trees of Tapezco expedition), 1Ψ, 1ɗ, ( LACM ENT /246784 /246792); idem , 21.iii.1978 (J.P. Donahue, D. Panny, D. Moelller, C. Lewis, LACM /Earthwatch trees of Tapezco expedition), 3Ψ, ( LACM ENT /246785 /246786 /246787); Puntarenas : Porto Cortés (Cuesta del Burro), 6.vi.2005 (J. Montero, B. Gamboa, J. Gutierrez, M. Moraga, J. Azofeifa, Y . Cardenas, J. Mata ), 1Ψ, ( INBIO ); Golfito, 30.xi–01.xii.2007 (J.A. Azofeifa), 1ɗ, ( INBIO ); Golfito, 29.ii–01.iii.2008 (J.A. Azofeifa), 1ɗ, ( INBIO ); (1,8 mi. W of Rincon Osa Peninsula, Puntarenas province), 15.ii.1971 (J. P. Donahue, C. L. Hogue), 1Ψ, Chlorotabanus mexicanus Linn. ( sic. ) det. Fairchild, 1972 ( LACM ENT / 246777); TRINIDAD and TOBAGO . [?] : undated (Urich), 1ɗ, Chlorotabanus mexicanus det. J. E. Chainey, 1992 (NHM); Sangre Grande (Vega de Oropuche), 20.ix. [19]57 (B. W. I., T. H. G. Aitken ex Bull, Cornelius B. Philip Collection Donated to California Academy of Sciences), 2Ψ, Chlorotabanus mexicanus det. Aitken, [19]57 ( CAS ); idem , Sangre Grande (Rio Grande Forest), 21.x. [19]57 (T. H. G. Aitken Coll ex Bull, Dusk, Cornelius B. Philip Collection Donated to California Academy of Sciences), 1Ψ, Chlorotabanus mexicanus det. Aitken, [19]57 ( CAS ); PANAMÁ . Barro Colorado, 15.v.1964 (Duckworth), 1Ψ, 2ɗ, ( USNM ); El Real Darien, 07.ii. [19]40 (unknown), 1Ψ, ( USNM ); Bocas del Toro , (Almirante), 28.x. [19]63 (unknown), 1Ψ, Chlorotabanus mexicanus (L.) det. G. B. Fairchild, 1981 ( INPA ); idem , 19.xi. [19]63 (unknown), 1Ψ, Chlorotabanus mexicanus (L.) det. Coscarón, [19]74 ( INPA ); idem , (Robalo), 26.i. [19]46 (unknown, Cornelius B. Philip Collection Donated to California Academy of Sciences), 1Ψ, Chlorotabanus mexicanus L. ( sic. ) (without det.) ( CAS ); Panamá Prov. , Moja Pollo, 15.iv. [19]40 (unknown, Cornelius B. Philip Collection Donated to California Academy of Sciences), 1Ψ, Chlorotabanus mexicanus L. ( sic. ) det. Fairchild, 1941 ( CAS ); idem , 27.iv. [19]40 (unknown, Cornelius B. Philip Collection Donated to California Academy of Sciences), 1Ψ, ( CAS ); Piña Area, 18.xi. [19]57 (W. J. Hanson), 1Ψ, Chlorotabanus mexicanus L. ( sic. ) det. Fairchild, 1970 ( UMNH ); idem, 21.x.1958 (W. J. Hanson), 1Ψ, ( UMNH ); Salud, 6.ix. [19]45 (K. E. Frick), 2Ψ, Chlorotabanus inanis Fabr. ( sic. ) det. C. B. Philip ( CAS ); SURINAME . [Marowijne] : Albina, 26.xi.1926 (R. N. Savory), 1Ψ, (NHM); (Langaman Kondre), viii.1965 (B. Malkin), 1Ψ, ( MZSP ); idem , (Christian Kondre), x.[1]963 (B. Malkin), 1Ψ, ( MZSP ); Paramaribo , 28.x.1957 (P. H. v. Doesburg Jr., Cornelius B. Philip Collection Donated to California Academy of Sciences), 1Ψ, ( CAS ); FRENCH GUIANA . Cayenne, iii.1917 (unknown, Acc. 5873, Cornelius B. Philip Collection Donated to California Academy of Sciences) Compared With Type Ψ T. olivaceus De G. ( mexicanus L.) May 1950 C. B. Philip, Almost ident, (over) except type brown due to age, 3rd a segs. Missing in th, 1Ψ, ( CAS ); Kourou , (Kuorou Forêt), 25.viii.1975 (Mission M. Boulard et P. Pompanon), 2ɗ, ( MNHN ); idem , (Cr. Des Peres), 4– 5.xi.1975 (Mission M. Boulard et P. Pompanon), 1ɗ, ( MNHN ); S[ain]t-Laurent [du] Maroni , (Acarouany prés de), 27.ix.2000 (D. Pluot-Sigwalt réc), 1Ψ, ( MNHN ); idem , (Forêt D’Acarouany / chasse de nuit / 10 km de la Leproserie, tubes u. v.), 18.ix.1969 ( Guyane Mission / Balachowsky-Gruner / Oct-nov 1969), 2Ψ, Chlorotabanus mexicanus (without det.) ( MNHN ); BRAZIL . Pará , Chaves (Ilhas Cavianas, Armadilha Malayse), 22.i. – 10.ii.1992 (M. Fernandes), 1Ψ, C. mexicanus det. I. S. Gorayeb ( MPEG ); idem , Viseu (Faz.[enda] Ema, 52°21’29,6’’S ; 01°25’13,5’’W , Malaise, na Mata ), 24.xi a 7.xii.1999 (I. S. Gorayeb, T. Pimentel, R. N. Bittencourt, J. O . Dias), 2Ψ, ( MPEG ), Ψ, ( INPA ); ECUADOR . Zapallo Grande (Rio Cayapas), 14.vii.1986 (unknown), 1Ψ, Chlorotabanus prob. mexicanus det. J. E. Chainey, 1986 (NHM); Discussion: widespread geographically, from southern Mexico to Brazil (Pará), apparently preferring coastal regions. Very polymorphic, with variations in color, antenna, frons and spots on the scutum and wings. The large number of intermediate specimens and their geographical overlap support the suggestion that C. mexicanus is polymorphic species. Comments (about Holotype ) . The Fairchild and Burger (1994) catalog suggests that the type for C. mexicanus is in Stockholm (NHRS). However, when we requested this specimen on loan, we were informed that it is not in that collection, which only contained the type for T. olivaceus DeGeer. We contacted others, including Drs. Bert Viklund and Bert Gustafsson (NHRS), Drs. David Notton and Theresa Howard (NHM) and Dr. Mike Fitton (Linnean Society) without discovering the location of the type specimen. The type for C. mexicanus is probably the same specimen as T. olivaceus DeGeer ( Philip & Fairchild 1956 ) . This is not surprising, considering that it is possible that DeGeer renamed species as he deemed most appropriate ( Philip 1952 ). Upon examining the type T. olivaceus , Philip (1952) noted two labels, “ Tabanus olivaceus DeGeer ” and “ mexicanus L.”. Due to the poor condition of the holotype of T. olivaceus , only photographs were sent (NHRS) and which were similar to the specimens of C. mexicanus used here in this study.