Examination with a binocular microscope of adults of Rhyssomatus subtilis Fielder (Coleoptera: Curculionidae) revealed distinct differences between the sexes in the foreleg, which permits their differentiation with complete accuracy. In the female the profemual process is weak, subacute, angulate and the protibia has an uncus and mucro. In the male the profemur process is strong, curved, subacute, tooth-like and lacks an protibia uncus.La examinación con microscopio binocular de los adultos de Rhyssomatus subtilis Fielder (Coleoptera: Curculionidae) revelan diferencia entre los sexos en las patas delanteras, permitiendo diferenciarlos con completa precisión. Las hembras presentan el proceso femoral anterior débil, subagudo, angulado y la protibia con uncus y mucro presente. En los machos el proceso femoral anterior es fuerte, curvado, subagudo, con diente y la protibia no presenta uncus.Fil: Cazado, Lucas Emiliano. Gobierno de Tucumán. Ministerio de Desarrollo Productivo. Estación Experimental Agroindustrial Obispo Colombres; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tucumán. Instituto de Tecnología Agroindustrial del Noroeste Argentino; Argentina; ArgentinaFil: O'brien, Charles W..Fil: Casmuz, Augusto S.. Gobierno de Tucumán. Ministerio de Desarrollo Productivo. Estación Experimental Agroindustrial Obispo Colombres; ArgentinaFil: Gastaminza, Gerardo A.. Gobierno de Tucumán. Ministerio de Desarrollo Productivo. Estación Experimental Agroindustrial Obispo Colombres; ArgentinaFil: Murúa, María Gabriela. Gobierno de Tucumán. Ministerio de Desarrollo Productivo. Estación Experimental Agroindustrial Obispo Colombres; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tucumán. Instituto de Tecnología Agroindustrial del Noroeste Argentino; Argentina; Argentin

Casmuz, Augusto S.

Cazado, Lucas Emiliano

Gastaminza, Gerardo A.

Murúa, María Gabriela

O'brien, Charles W.

Florida Entomologist

Lucas E. Cazado

Charles W. O'Brien

Augusto S. Casmuz

Gerardo A. Gastaminza

M. Gabriela Murúa

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Sexual Dimorphism of<i>Rhyssomatus subtilis</i>(Coleoptera: Curculionidae)

CONICET Digital

1812 Florida Entomologist 97(4) December 2014sexual Dimorphism of Rhyssomatus subtilis  (Coleoptera: CurCulioniDae)Lucas E. cazado1, 3, charLEs W. o’BriEn2, augusto s. casmuz1,  gErardo a. gastaminza1  and m. gaBriELa murúa1, 3  1sección Zoología agrícola, estación experimental agroindustrial obispo Colombres, las talitas (t4104auD), tucumán, argentina22313 W. Calle Balaustre, Green Valley, aZ 85622-8047, usa3itanoa-ConiCet-eeaoC, instituto de tecnología agroindustrial del noroeste argentino- Consejo nacional de investigaciones Científicas y técnicas*Corresponding author; e-mail: lcazado@eeoac.org.araBstractexamination with a binocular microscope of adults of Rhyssomatus subtilis fielder (Cole-optera: Curculionidae) revealed distinct differences between the sexes in the foreleg, which permits their  differentiation with complete accuracy. in the female the profemual process is weak, subacute, angulate and the protibia has an uncus and mucro. in the male the profe-mur process is strong, curved, subacute, tooth-like and lacks an protibia uncus.Key Words: weevil, uncus, mucro, tibiae, femoral processrEsumEnla examinación con microscopio binocular de los adultos de Rhyssomatus subtilis fielder (Co-leoptera: Curculionidae) revelan diferencia entre los sexos en las patas delanteras, permitiendo diferenciarlos con completa precisión. las hembras presentan el proceso femoral anterior débil, subagudo, angulado y la protibia con uncus y mucro presente. en los machos el proceso femoral anterior es fuerte, curvado, subagudo, con diente y la protibia no presenta uncus.palabras Claves: picudo, uncus, mucrones, tibia, proceso femoralthe black soybean weevil, Rhyssomatus sub-tilis fiedler (Coleoptera: Curculionidae), is an important pest of soybean in northwestern argentina (nWa), which is expanding its geo-graphical distribution and causing economic losses through the extensive reduction of yields (Cazado et al. 2013). the recent growth and spread of R. subtilis populations has called at-tention to the need for conducting more studies on the biology, behavior and ecology of the pest. as a preliminary step for these studies, it is necessary to determine the sex of adult weevils without resorting to the dissection of their geni-talia. this requires finding a quick method for identifying the sex of these insects which would keep handling to a minimum (silva- filho et al. 2007).several techniques for sexing weevils have been discovered, but they differ notably from one another (sappington et al. 2000). internal morphology can be used to determine sex, but dissection is a tedious process which involves killing the weevils (Klassen et al. 1968; Jones et al. 1992). in some studies, sex was determined by watching weevils copulate (mitchell 1963), but this method turns out to be impractical or-dinarily. the genitalia can be partially extrud-ed by squeezing the abdomen of some weevils, but this procedure usually injures the weevil, especially as the cuticle hardens with age (agee 1964). it is not especially useful in most molyti-nae such as Rhyssomatus due to the hard inflex-ible cuticle of the elytra and abdomen.When dealing with the Curculionidae, there are various external sex characters that can be considered in order to determine the sex of weevils (hoffman 1950; silva- filho et al. 2007). for Cosmopolites sordidus Germar, the angle of inclination of the last abdominal sternite and distribution of pubescence over the frons are taken into account (longoria 1968). in the case of anthonomus grandis Boheman and other species of anthonomus, the focus is on differ-ences in the tarsal claws (agee 1964; Kovarik &  Cazado et al.: sexual Dimorphism of Rhyssomatus subtilis 1813Burke 1983). the presence of a thorn directed behind the legs on each intermediate coxa helps to identify male anthonomus rubi herbst (in-nocenzi et al. 2002), whereas male anthonomus eugenii Cano are recognized based on their metatibial mucro, which is larger and more prominently curved than those of the female (eller 1995).some species of the molytinae possess a mucro, a secondary tooth located at the inner apical angle of the uncinate tibiae. thus, a par-ticular tibia can have both an uncus and a mu-cro (Kuschel 1952; thompson 1992).the shapes and positions of the uncus, mucro and premu-cro in the genus tyloderma, Cryptorhynchinae distinguishes sexes and species groups (Wibmer 1981, 1989).this study identifies some external second-ary sexual characters that are readily detect-able and that form the basis for an accurate and non-disruptive technique for sexing adult R. subtilis.matEriaLs and mEthodsall adult weevils were collected from an emergence cage placed in a soybean field in ro-sario de la frontera (salta province, argentina) (s 25° 39' 57.6" -W 64° 56' 58.1"), between nov and Jun in 2010/2011 and 2011/2012. adults were preserved in 70% ethanol and kept in it until they were examined in the laboratory.in order to find secondary sexual characters of R. subtilis adults, the external characters of the specimens were examined, using the meth-odology proposed by other authors for deter-mining sexual dimorphism of the Curculionidae (Kuschel 1952; rosado-neto 1987; loja Cedeño 2011). putative differences observed were veri-fied by inspection of the genitalia, by means of a binocular microscope (Zeiss model stemi DV4) with 10x magnification. for genital dissection, individuals were macerated and cleared in a Koh solution (10%) for 15 min, at 80 °C to pro-mote dissolving of fat tissue, thus facilitating visibility of the reproductive structures as de-scribed by Castañeda-Vildózola et al. 2007.rEsuLtsafter examining 1,768 R. subtilis adults col-lected from the emergence cage, we found that the external characteristics of the apical ar-mature of the fore tibia was useful for sexual determination (fig. 1). results showed a 100% concurrence with those reached by examining genitalia. the apical margin of the protibia of the female has a subcarinate ridge ending in an elongate, subacute uncus projecting posteriad, and has an acute mucro on the inner apical an-gle, partly concealed by 2 clusters of coarse se-tal brushes anterior and posterior to the mucro. the male has no uncus on the protibia, and all of its tibiae have only a mucro (fig. 1). in addi-tion, it was found that the difference in the pro-femoral process is striking between the sexes. in the female the process is weak and angulate and that of the male is strong, curved, subacute and tooth-like. By observing these differences with the aid of a 10x binocular microscope, it is possible to determine the sex of adult weevils via this quick, accurate and non-destructive technique, which keeps handling to a minimum.the adult weevils were placed frontally facing the microscope lens, and without exerting too much pressure with the index finger, they were held firmly so that their forelegs spread out. this procedure allowed one to observe the presence or absence of the uncus on the protibia, as well as the different profemoral process (fig. 1).discussionBased on these results, external protibial morphology provides characters for the accu-rate differentiation of male and female R. sub-tilis adults.this observation is in agreement with those of other authors, who reported that the pres-ence or absence of the uncus, mucro, and pre-mucro is a set of characters to be considered in order to determine sexual dimorphism in various species of the Curculionidae, such as sternechus subsignatus (rosado-neto 1987), and Chalcodermus bicolor fiedler 1936; loja Cedeño 2011), as well as numerous species of the genus bondarius (Dos-santos 2007).the presence of a modified metatibial mucro is a secondary sexual character of male lissor-rhoptrus and its form, and shape and number of processes is species specific as well (Kuschel 1952; everett & newsom 1964, o’Brien & has-eeb 2014).Determining sex of R. subtilis adults through external characters as described and illustrated here is as accurate as genital dissection, consti-tuting a very quick and non-destructive tech-nique, which involves practically no handling of the live insects.therefore, this information and the proposed technique should make great contributions to biological and behavioral studies, including re-search on aggregation pheromones in this spe-cies and studies of the economic losses caused by this soybean pest.acknoWLEdgmEntsWe thank lic. e. Willink for constructive comments on an earlier draft of the manuscript. appreciation is also expressed to alejandro Vera the sección Zoología 1814 Florida Entomologist 97(4) December 2014agrícola of estación experimental agroindustrial obispo Colombres (eeaoC), tucumán – argentina for providing the photographic images. this study was sup-ported by eeaoC and Consejo nacional de investiga-ciones Científicas y técnicas (ConiCet) of argentina and it is part of the first author’s doctoral thesis.rEfErEncEs citEdagEE, h. r. 1964. Characters for determination of sex of the boll weevil. J. econ. entomol. 57: 500-501.castañEda-ViLdózoLa, a., VaLdEz-carrasco, J., Equihua-martínEz, a., gonzáLEz-hErnándEz, h., romEro-nápoLEs, J., soLís-aguiLar, J. f., and ramírEz-aLarcón, s. 2007. Genitalia de tres espe-cies de heilipus Germar (Coleoptera: Curculionidae) que dañan frutos de aguacate (Persea americana mill) en méxico y Costa rica. neotrop. entomol. 36: 914-918cazado, L. E., murúa, m. g., casmuz, a. s., socías, m. g., VEra, m. t., o’BriEn, c. W. and gasta-minza g. 2013. Geographical distribution and new associations of Rhyssomatus subtilis (Coleoptera: Curculionidae) in argentina. florida entomol. 96: 663-669.dos- santos, g. B. 2007. revisão e análise cladística de bondarius rosado neto, 2006 (Coleoptera: Cur-culionidae, molytinae, sternechini). tesis de mae-stría. universidad federal do paraná, Curitiba, pr, Brasil.ELLEr, f. J. 1995. a previously unknown sexual char-acter for the pepper weevil (Coleoptera: Curculioni-dae). florida entomol. 78: 180-185.EVErEtt, t. r., and nEWsom, L. d. 1964. external characters for separating the sexes of the rice wa-ter weevil, lissorhoptrus oryzophilus (Coleoptera: Curculionidae). ann. entomol. soc. america 57: 514-515.hoffman, a., 1950. Coléoptères Curculionides in ier partie. faune de france 52: 486 pp. lechevallier edit. paris.innocEnzi, p. J., haLL, d. r., cross, J. V., and grEEn, s. V. 2002.sexing adults of the strawberry blossom weevil, anthonomus rubi (Col., Curculionidae). J. appl, entomol. 126(4): 159-160.JonEs, r. W., catE, J. r., hErnandEz, E. m., and na-Varro, r. t. 1992. hosts and seasonal activity of the boll weevil (Coleoptera:Curculionidae) in tropical and subtropical habitats of northeastern mexico. J. econ. entomol. 85: 74-82.fig. 1. anterior view (a) and posterior view (B) female weevil: profemur with weak, subacute, angulate, internal process and protibia with uncus and mucro present; and anterior view (C) and posterior view (D) of male weevil: profemur with strong, curved, subacute, tooth-like, internal process and protibia lacking an uncus. Cazado et al.: sexual Dimorphism of Rhyssomatus subtilis 1815kLassEn, W., norLand, J. f., and BořkoVEc, a. B. 1968. potential chemosterilants for boll weevils. J. econ. entomol. 61: 401-407.koVarik, p. and BurkE, h. r. 1983. sexual dimorphism of tarsal claws in anthonomine weevils (Coleoptera: Curculionidae). entomol. news 94: 37-40.kuschEL, g. 1952. revisión de lissorhoptrus leconte y géneros vecinos de america. rev. Chilena entomol. 1: 23-74.LoJa cEdEño, p. E. 2011. Biología e manejo de Chal-codermus bicolor fiedler (Coleoptera: Curculioni-dae: molytinae), em plantios de eucaliptus. tesis de maestría inédita. universidad federal de Viçosa, em Viçosa, mina Gerais, Brasil.Longoria, a. g. g. 1968. Diferencias sexuales en la morfología externa de Cosmopolites sordidus Germar (Coleoptera: Curculionidae). Ciências, serie 4, ha-bana 1:11.mitchELL, E. B., and hardEE, d. d. 1974. in-field traps: a new concept in survey and suppression of low popu-lations of boll weevils. J. econ. entomol. 67: 506-508.o’BriEn, c. W., and hasEEB, m. 2014. revision of the “rice water weevil” genus lissorhoptrus leConte in north america, north of mexico (Coleoptera: Curcu-lionidae). Coleopts. Bull. 68: 163-186.rosado nEto, g. h. 1987. Dimorfismo sexual e distri-buição geográfica de sternechus subsignatus Bohe-man, 1936 (Coleoptera: Curculionidae) no Brasil. an. soc. entomol. Brasil 16: 199-204.sappington, t. W., and spurgEon, d. W. 2000. pre-ferred technique for adult sex determination of the boll weevil (Coleoptera: Curculionidae). J. econ. en-tomol. 93: 610-615.siLVa-fiLho, g., BaiLEz, o. E., and Viana-BaiLEz, E. a. m. 2007. Dimorfismo sexual do gorgulho-da-goiaba Conotrachelus psidii marshall (Coleoptera: Curcu-lionidae). neotrop. entomol. 36:520-524.thompson, r. t. 1992. observations on the morphol-ogy and classification of weevils (Coleoptera: Curcu-lionoidea) with a key to major groups. J. nat. hist. 26: 835-891.WiBmEr, g. J. 1981. revision of the new World weevil genus tyloderma in america north of mexico (Cole-optera: Curculionidae: Cryptorhynchinae). south-western entomologist, suppl. 3: 1-95.WiBmEr, g. J. 1989. revision of the weevil genus ty-lodina say (Col.: Curculionidae) in mexico, Central america, south america, and the West indies. evol. monogr. 11: 1-118.

Sexual Dimorphism of Rhyssomatus subtilis (Coleoptera: Curculionidae)

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Sexual Dimorphism of Rhyssomatus subtilis (Coleoptera: Curculionidae)

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