Key to higher taxa of South American weevils based on adult characters ( Coleoptera , Curculionoidea )

The weevils (Coleoptera: Curculionoidea) from South America are currently classified in the following families and subfamilies: Nemonychidae (Rhinorhynchinae), Anthribidae (Anthribinae), Belidae (Belinae and Oxycoryninae), Attelabidae (Attelabinae and Rhynchitinae), Brentidae (Apioninae and Brentinae), Caridae (Carinae) and Curculionidae (Erirhininae, Dryophthorinae, Entiminae, Aterpinae, Gonipterinae, Rhythirrininae, Thecesterninae, Eugnominae, Hyperinae, Curculioninae, Cryptorhynchinae, Mesoptiliinae (= Magdalidinae), Molytinae, Baridinae, Lixinae, Conoderinae (= Zygopinae), Cossoninae, Scolytinae and Platypodinae). In the present contribution we bring a dichotomous key for the identification of seven families and 28 subfamilies of Curculionoidea from South America, and for 21 tribes of the highly heterogeneous subfamilies Curculioninae and Molytinae. These tribes are Curculionini Anthonomini, Ceutorhynchini, Derelomini, Otidocephalini, Erodiscini, Camarotini, Piazorhinini, Prionobrachiini, Smicronychini, Rhamphini and Tychiini, within Curculioninae; and Hylobiini, Pissodini, Conotrachelini, Cleogonini, Sternechini, Pacholenini, Cholini, Petalochilini and Amalactini, within Molytinae. Most of them have been classified as subfamilies in traditional schemes. The key is mainly based on external morphological characters, but also includes data on genitalia, mouth parts and other biological features. Definitions and illustrations of diagnostic characters used in the key are provided.


INTRODUCTION
The weevils are beetles of the superfamily Curculionoidea, mostly phythophagous as both, adult and larval stages.They comprise about 60,000 described species gathered in 6,000 genera.Approximately 10,000 species occur in South America, assigned to about 1,000 genera (Wibmer & O'Brien 1986, Alonso-Zarazaga & Lyal 1999).
The current classification of weevils is under continuous revision, due to new characters provided by adult and larval morphology, the addition of molecular data, and the analysis of this information applying a phylogenetic approach, such as those of Thompson (1992), Zimmerman (1993Zimmerman ( , 1994aZimmerman ( , 1994b)), Kuschel (1995), Lawrence & Newton (1995), Marvaldi & Morrone (2000) and Marvaldi et al. (2002).The majority of recent classificatory schemes agree in the circumscription of the main higher groups of Curculionoidea, but they differ in the assignment of ranks and/or the evaluation of the monophyletic status of some heterogeneous subfamilies and tribes.
Keys available for the identification of higher taxa of Curculionoidea are either no updated according to the new classificatory schemes (Costa-Lima 1956), and/or were designed for taxa occurring in geographical latitudes out of South America (Morimoto 1962a, Kissinger 1964, Anderson 2002).A key to identify Argentinian weevils published by Morrone & Posadas (1998) is mostly suitable for taxa at family rank, and the key for South American weevil families and subfamilies published by Marvaldi (2003) is for the larval stage exclusively, and thus complementary of the present key for adults.
The purpose of this paper is to provide a key to identify the families and subfamilies of South American Curculionoidea, and several tribes of the highly heterogeneous subfamilies Curculioninae and Molytinae (Curculionidae), using adult morphological characters.
In the "World catalogue of genera of Curculionoidea" published by Alonso-Zarazaga & Lyal (1999) the authors recognized 22 families, following the classification of Thompson (1992) and Zimmerman (1993Zimmerman ( , 1994aZimmerman ( , 1994b)).In this contribution we have recognized seven families, according to the phylogenetic proposals of Kuschel (1995), Marvaldi & Morrone (2000) and Marvaldi et al. (2002).As a consequence, some taxa herein treated as subfamilies (i.e., Oxycoryninae, Rhynchitinae, Apioninae, Dryophthorinae, Erirhininae, and Platypodinae) were considered with a family rank by Alonso-Zarazaga and Lyal.Other differences between the classification of the mentioned catalogue and the one herein adopted are as follows: the concept of Entiminae excludes Thecesterninae (Marvaldi 1997), the concept of "Curculioninae" excludes Eugnominae (Marvaldi, unpublished data), and Aterpinae, Rhythirrininae and Gonipterinae are treated as independent subfamilies instead of tribes of Cyclominae.
All the taxa were keyed out a single time except Curculioninae, which was keyed out in four couplets.To check the key, we have used material deposited at the entomological collections of the Museo de La Plata (MLP) and the Instituto Argentino de Investigaciones de las Zonas Áridas (IADIZA-CRICYT).
Most characters used in the key are e x t e r n a l m o r p h o l o g i c a l f e a t u r e s e a s i l y visible under a stereo-microscope.In some instances, the observation of the genitalia is needed (previous dissection) to ensure correct identifications (e.g., Erirhininae).
The terminology to designate different structures and body parts mentioned in the key is indicated mainly in Fig. 1, and the diagnostic characters are diagrammatically illustrated (Fig. 2 to 10), except details of the vestiture.

Structures and taxonomic characters
Antennae (Fig. 2).The typical antennae of the Curculionoidea has 11 articles, but the basic number is 12, being the last article usually fused with article 11.The basal article is the "scape", followed by the "funicle" of seven articles, and by a three articulated terminal "club" (Fig. 1A).In most weevils except Curculionidae (e.g., Nemonychidae, Anthribidae, Belidae, Attelabidae, Caridae, and Brentidae) the antennae are straight, with a scape quite short (about as long as funicular article 1) and the funicle joined in line with the scape (Fig. 2A to 2C, 2G and 2H).In Curculionidae the antennae are geniculate (= elbowed), with the scape elongate (distinctly longer than funicular article 1) and the funicle obliquely joined to the scape (Fig. 2D and 2E).
The number of funicular articles can be reduced to six, five or even four, in some weevil taxa.For example in Dryopthorinae the funicle has six or less articles, because the last funicular article is added to the club, forming a basal shiny portion of it (Fig. 2E).The club may be compact, as in Curculionidae (Fig. 2D), or loosely articulated as in most basal families (Fig. 2A and 2B).In the latter case the club may be indistinct when its articles are similar to those of the funicle, e.g., in some Belidae (Fig. 2A), but the club articles are usually recognised for being wider and more pilose (Fig. 2B and 2H).The males of Cylas formicarius (Fabricius) (Brentidae, Cyladinae) have a particular antenna with nine articles followed by a very elongate club formed by articles 10-11 (Fig. 2C).
Antennae are usually inserted between midlength and apex of the rostrum (Fig. 2F), and in some cases near rostral base (Fig. 2G).The insertion is mostly lateral, but some weevils have dorsal or ventral (Fig. 2H) antennal insertions.
Rostrum (Fig. 3).The presence of a rostrum extended beyond the eyes, with mouth-parts situated at its apex, is one of the most typical features of Curculionoidea (Fig. 1C).The shape, length and width of the rostrum show great variation among weevil taxa, from long and slender (e.g., "long-nosed weevils", as Curculioninae) (Fig. 3C) to short and broad (e.g., "broad-nosed weevils, as Entiminae) (Fig. 3B), and it can be reduced or even absent (Fig. 3A) in some specialised groups (e.g., Scolytinae, Platypodinae).The rostrum is frequently sexually dimorphic, particularly in those weevils that use it for oviposition site preparation (e.g., in females the rostrum is usually longer and with antennal insertion more basal than in males).
The lateral rostral grooves for the reception of the scape in repose are called "scrobes" (Fig. 1C), which may have different extension and curvature (Fig. 3B to 3E).
Some weevils have a ventral cavity or sternal channel for the reception of the rostrum in repose (Fig. 3F and 3G).The channel may be only prosternal, it can also comprise the mesosternum, and in some few cases it extends to the metasternum, or even further, towards ventrites.In Cryptorhynchinae, the channel ends in a cup-like receptacle (Fig. 3G).
Ventral surface of head and mouth-parts (Fig. 4).In most weevils, the ventral surface of the head has a single median gular suture (Fig. 4E), anteriad to postoccipital suture, and thus the gula is indistinct (see Lyal 1995).Only in some basal weevils (e.g., Nemonychidae, Belidae) the gular sutures are separate (Fig. 4G) and delimite a gular sclerite or gula, located between the submentum and the neck membrane.
Mouth-parts are located at the apex of the rostrum (Fig. 1B).The labrum and the clypeolabral suture (dorsal view) are indistinct in most Curculionoidea (Fig. 4B), except in Nemonychidae and Anthribidae (Fig. 4A).The labium (ventral view) has a prementum, which can be pedunculate, and a posterior sclerite called submentum, also regarded as "pregula" (Fig. 4E).The extent to which the labial prementum covers the maxillae determines two types of mouth-parts: in the Adelognathous type the maxillae are hidden by a enlarged prementum (Fig. 4D), and in the Phanerognathous type the maxillae are visible continuously at sides of the prementum (Fig. 4E).When the prementum is relatively small, it is usually pedunculate (Fig. 4E).Characters of the labial and maxillary palpi, such as insertion, direction and number of articles are useful as taxonomic characters at family and subfamily levels.The maxillary palpi are elongate and projecting in those basal weevils with a distinct labrum (Fig. 4C), and compact in the remaining curculionoids (Fig. 4D, 4E and 4F).The mandibles are relatively large, robust, and setose and/or squamose in "broad-nosed weevils", and usually smaller, glabrous or with few setae in "long-nosed weevils".Moreover, the mandibles of broad-nosed weevils usually bear a scar, left by a deciduous process (Fig. 4D).These processes or cusps have different sizes and shapes (see Thompson 1992), being presumably used by the adult to emerge from the pupal cell and to dig its way out of the soil.They are subsequently lost by active dehiscence when feeding takes place.
The inner margin of the mandibles is usually dentate, but the outer edge is not (Fig. 4A and 4E), except in some groups such as Rhynchitinae, with exodontous mandibles (with teeth on outer edge) (Fig. 4B).In most weevils the mandibles are attached laterally, having a quite horizontal movement, but in Curculionini the attachment point is located dorsally and the mandibles move vertically.
The frons may be broad (Fig. 5G) or narrow (Fig. 5F) depending on the relative size and proximity of the eyes.In some taxa there are superciliar arcs (e.g., some Aterpinae), preocular or postocular constrictions or impressions, or postocular lobes (e.g., Rhythirrininae) (Fig. 3E).The postocular lobes are projections of the antero-lateral margins of the pronotum, that could partially conceal the eyes (Fig. 5D).
The head usually extends a short distance from posterior margin of the eyes to the anterior margin of the pronotum, but sometimes (e.g., in most Eugnominae, some Brentinae) it is markedly prolonged behind the eyes (Fig. 6A).It could be as wide as the pronotum or narrower than the pronotum, visible from dorsal view (Fig. 5I) or concealed by the pronotum (Fig. 5J).
Elytra could be abbreviated, leaving terminal tergites (pygidium) uncovered (Fig. 7D and 7E).In Mesoptiliinae, the elytral base is extended forward, concealing the base of the pronotum (Fig. 7D).In some taxa with ascending mesepimeron, this pleural sclerite is seen between the basal angles of the pronotum and the elytra (Fig. 7E).Elytral striae are usually 10, numbered from the suture to the elytral margin (Fig. 1A, 7D and 7G).The spaces between striae are called intervals or interstriae.Irregularly punctuated elytra have indistinct striae, and in certain species there are supernumerary striae.
Another useful sclerite is the metepimeron, which may be exposed (Fig. 7F) or covered by the elytra (Fig. 1C).In the latter case, its vestiture is thinner and sparser than that of the metepisternum.
Legs (Fig. 8 and 9).Legs provide numerous diagnostic characters for the identification of higher taxa of Curculionoidea (Fig. 1A and  1B).The front coxae may be contiguous (Fig. 1B), subcontiguous (Fig. 8A), or separate from each other (Fig. 8C).The trochanter is usually reduced and subtriangular, with the femur attached to its side (Fig. 8C); in Apioninae the trochanter is conspicuous and subcylindrical, with the femur attached to its apex (Fig. 8D).The three pairs of femora are either similar to each other, or the front or hind femora are different by being distinctly broader, longer or by having a large tooth, e.g., Curculioninae of the tribes Camarotini, Prinonobrachiini (Fig. 8E) and Rhamphini (Fig. 8F).The front legs frequently show sexual dimorphism, being thicker and longer in the males.Tibial apex (Fig. 9A to 9M).The tibia may be apically unarmed, or it can bear an apical tooth (mucro) (Fig. 9A), a hook (uncus) (Fig. 9C) or one or two spurs (Fig. 9B).These processes can be recognized as follows: mucro (Fig. 9A), a tooth-like process arising from the inner apical angle, not continuous with the outer tibial margin.Mucronate tibiae are common among leaf-cuting or ground-dwelling curculionoids, such as many broad-nosed weevils (e.g., Entiminae, Rhythirrininae); uncus (Fig. 9C and 9E), a hook-like process (curved spine) arising from, or continuous with the outer apical angle of tibia.In some species the uncus is situated more inwards (in the middle or closer to the inner apical angle) and therefore, can be confused with a mucro.If it is also not stoutly curved, then the aspect of the apical comb of setae may help to recognize the uncus condition (see below).Uncinate tibiae are mainly present in weevils associated with wood or bark that use to climb trunks (e.g., Molytinae, Cryptorhynchinae); premucro (Fig. 9E), a secondary tooth, located on the inner apical angle of the uncinate tibiae (Kuschel 1951, Thompson 1992), thus, a particular tibia can have both, uncus and premucro (e.g., some Molytinae).The base of the premucro is usually flanked by a pair of tufts of long setae (Fig. 9E).
Based on comparative studies, it has been proposed that mucro and uncus are homologous (Kuschel 1951, Thompson 1992), corresponding to the same structure (apical tooth) with different degrees of development and placement.Since homologous structures cannot co-occur in the same organism according to the criteria of conjunction (Patterson 1982), it follows logically that a particular tibia cannot be both mucronate and uncinate, then, mucro and uncus are different states of the same character.On the contrary, uncus and premucro are non-homologous, and can take place in the same tibia.
Tibial combs (Fig. 9A, 9B and 9E).The tibiae of weevils usually have rows of modified setae at the apex, around the tarsal articulation, except in some groups such as Cossoninae (Fig. 9C).The apical comb of setae is generally more developed on the hind tibiae, and it can be oriented either transversely (Fig. 9A and 9B) or obliquely to subparallel (Fig. 9E) regarding the tibial axis.When mucronate and uncinate conditions are not clear, the apical comb of setae may help to discriminate between them: In mucronate tibiae the apical comb is transverse (Fig. 9A and 9B) and curved; in uncinate tibiae the apical comb can be present or absent, if present, it is usually oblique or subparallel to tibial axis (Fig. 9E), and it is not or only slightly curved (Marshall 1932, Kuschel 1951, Thompson 1992).Besides the previously described processes, the front tibae of some weevil taxa (e.g., Belidae, Curculionidae Cossoninae) have particular grooming devices (Fig. 9F to 9I).
Tarsi (Fig. 9A to 9M).Curculionoidea have five tarsal articles (tarsites), but in most cases the tarsi appear to be four segmented (pseudotetramerous) (Fig. 1B) because tarsite 4 is minute and concealed between the usually bilobate tarsite 3; tarsite 5 usually bears a pair of claws (Fig. 9J to 9M), and exceptionally a single tarsal claw.Tarsal claws may be free (independent or separate from each other) (Fig. 9J, 9L and 9M), or connate (inner faces are contiguous in their basal half) (Fig. 9K); simple (Fig. 9J), or appendiculate (Fig. 9L) when they bear a process or tooth at the base, which in some cases can be as long as the claw.In Dryophthorinae there are dorsal and ventral lobes between the claws (Fig. 9M).
Abdomen and male genitalia (Fig. 10).Visible abdominal sternites are five (numbers three to seven), because sternites one and two have been absorved into the hind coxal cavity.They are usually called ventrites and numbered from one to five (Fig. 1B and 1C).In basal weevil families, the ventrites are usually free (not fused) and similar in length (see Thompson 1992), but in the majority of weevils the first two ventrites are fused together and are frequently larger than the remaining (Fig. 1B, 10A and 10B).Flexure of the venter has thus been increasingly concentrated on the short Abdominal tergites one-seven are located beneath the elytra and are less sclerotized than the sternites, with functional spiracles placed on their lateral areas.Tergite eight may be exposed or concealed (see Thompson 1992).In some groups with abbreviated elytra, one or two tergites are uncovered and usually sclerotized.The uncovered terminal tergites form the pygidium (Fig. 7D and 7E).