Key to larvae of the South American subfamilies of weevils ( Coleoptera , Curculionoidea ) Clave para larvas

The weevils (Coleoptera: Curculionoidea) from South America are classsified into seven families and 28 subfamilies as follows: 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). A dichotomous key for the larval stage is provided for identification of the families and subfamilies of Curculionoidea present in South America. The key is based on external morphological characters and contains data on larval feeding habits.


INTRODUCTION
The weevils are characteristic beetles of the Superfamily Curculionoidea, mostly phythophagous as both adults and larvae.They comprise about 60,000 species worldwide, grouped in 6,000 genera (Thompson 1992).In South America there are approximately 10,000 species described, in about 1,000 genera (Wibmer & O'Brien 1986, Alonso-Zarazaga & Lyal 1999).However, a very small proportion of genera and species are described at the larval stage.The knowledge on immature weevils is particularly scarce in South America, smallness compared with the high taxonomic diversity present in the area.Although this makes it not possible to identify the larvae of South American weevils to genus, representatives of the different families and subfamilies have now been described (e.g., Rosado-Neto 1980, Costa et al. 1988, May 1993, Marvaldi 1998a-c, Marvaldi & Morrone 1998, Lanteri et al. 2002).Identification of weevil larvae is important and necessary in systematic studies as well as in many other fields (Burke & Anderson 1976); it can contribute to studies in ecology, soilsciences, and applied entomology (such as pest management and biological control).The present key, to larvae of Curculionoidea present in South America, is aimed to identify representatives of this development stage at higher taxonomic level (family and subfamily).

Larvae of the Order Coleoptera
Beetle larvae are very diverse in morphology (see Lawrence 1991) but the following combination of features may distinguish them from those of other insect orders: Head capsule well-developed and sclerotized, with an ecdysial line (usually Y-shaped) that divides the cranium into a frons and two epicranial areas; antennae with four to one segments and a sensorium; stemmata (larval ocelli) in number of six or fewer on each side; mouthparts of the chewing type, with opposable mandibles, without labial silk glands; thoracic legs with six to fewer segments, sometimes vestigial or completely absent; abdominal prolegs almost always absent; abdomen with 10 segments, with segment IX variously modified (sometimes bearing paired dorsal processes or urogonphi), segment X reduced and without cerci; respiratory system usually with nine pairs of spiracles, placed on thorax (often on mesothorax) and on abdominal segments I-VIII.

Larvae of the Superfamily Curculionoidea
Most weevil larvae live inside dense substrates, like plant tissues, fungi, or soil, with few instances of aerial external feeding (Marvaldi et al. 2002).A morphological characterization of the Curculionoid larvae is as follows (Fig. 1 and 2): comma-shaped grubs; with soft (usually whitish) abdominal segments, the first seven or eight transversely divided into two to four dorsal folds or plicae; legs absent or vestigial; head hypognathous, with reduced antennae (usually one-segmented, rarely two-segmented, plus the sensorium); hypopharyngeal bracon present (except in some leaf-miners and platypodines); maxilla with a single apical lobe or mala; abdominal tergum IX without urogonphi; spiracles annular, with or without airtubes.
Comparative notes: larvae of some Chrysomeloidea [Cerambycidae, Megalopodidae, and Chrysomelidae (including Bruchinae)] can be confused with weevil larvae, but all of the former differ in lacking a hypopharyngeal bracon and most of them differ in having legs.Legless larvae of Cerambycidae, as well as those of Buprestidae, can be separated from weevil larvae by their straight body and enlarged prothorax.Larvae of Scarabaeoidea can be distinguished from weevil larvae on the basis of their strongly curved (Ushaped) body, well-developed legs, and cribiform and reniform spiracles.

Classification
Current classifications of weevils vary greatly in the number of families and subfamilies recognized, but the differences are mostly in rank and the concepts or genera included in each higher taxon generally agree (e.g., Thompson 1992, Zimmerman 1993, 1994a, 1994b, Kuschel 1995, Lawrence & Newton 1995).In the present paper the weevils are classified in seven families (Nemonychidae, Anthribidae, Belidae, Attelabidae, Caridae, Brentidae, and Curculionidae), according to recent phylogenetic studies (Kuschel 1995, Marvaldi et al. 2002).In the recent world catalogue of Curculionoidea (Alonso-Zarazaga & Lyal 1999), the genera are arranged into a larger number of families ( 22), mainly following Thompson (1992), and Zimmerman Fig. 2: A generalized weevil larva, lateral aspect.
Una larva de gorgojo generalizada, aspecto lateral.(1993, 1994a, 1994b).As a consequence, several subfamilies in the present paper (i.e., Oxycoryninae, Rhynchitinae, Apioninae, Dryophthorinae, Erirhininae, and Platypodinae) are considered to have family rank in the catalogue.Remaining subfamilies in Curculionidae are in agreement with the catalogue, with some minor differences: in the present work the concept of Entiminae excludes Thecesterninae (Marvaldi 1997), the concept of "Curculioninae" excludes Eugnominae (Marvaldi, unpublished data), and also the Aterpinae, Rhythyrrininae and Gonipterinae are kept as subfamilies instead of tribes of Cyclominae.A natural classification of the family Curculionidae into subfamilies still is incipient and some concepts of the subfamilies used herein, although practical for the purpose of identification in the key, may correspond to para-or polyphyletic taxa.

Characters and terminology
The key is based on external morphology.Information on larval habits, such as host tissues most frequently consumed, also is provided.Observation of most larval structures requires the larvae to be dissected and slide-mounted for examination under a compound microscope.Techniques to study larval material are provided in the references cited below.Generally it is necessary to separate the head, mouth-parts and cuticle, to clear them in KOH, transfer them to ethanol, and then place the pieces in glycerine or make permanent slides in euparal or a similar media.The morphology of a generalized weevil larva and terms used in the key are indicated in Fig. 1 and 2. The larval characters were gathered mainly from Costa et al. (1988), Anderson (1991a, 1991b, 1991c, 1991d), May (1993May ( , 1994)), Marvaldi (1997Marvaldi ( , 1998aMarvaldi ( , 1998bMarvaldi ( , 1998cMarvaldi ( , 1999)), Marvaldi & Morrone (1998), Lanteri et al. (2002), and many couplets are modified from May (1993).Terminology employed also follows those sources, as in Marvaldi (1999).

RESULTS AND DISCUSSION
The following key should be considered preliminary, since it could be tested with South American representatives for some but not for all of the subfamilies.However, it was developed with the aim to be useful for as many regions as possible, and given the conservative nature of most larval characters, I am confident that most couplets are predictive to South America.