CURCULIONOIDEA, Latreille, 1802

Davis, S. R., 2017, The Weevil Rostrum (Coleoptera: Curculionoidea): Internal Structure And Evolutionary Trends, Bulletin of the American Museum of Natural History 2017 (416), pp. 1-76 : 1-76

CURCULIONOIDEA (figs. 16–50)

Aside from the aforementioned structures, other consistent features among the weevils include the following: two longitudinal rows of muscles (the pharyngeal dilator muscles) dorsolateral to the pharynx; the pharyngeal circular muscles, which essentially envelop the pharynx, though they are limited to the dorsal and lateral surfaces where the pharyngeal plate is present; salivary glands (mandibular glands sensu Dönges, 1954) and the associated canals located lateral to the pharynx; several pairs of nerves and tracheae, such as the dorsalmost and often largest tracheal pair, t8, which most often are situated dorsolaterally to the pharynx.

The following descriptions highlight the main similarities and differences within the major weevil families and subfamilies (confined to those taxa sampled) concerning internal rostrum morphology. Given the multiple sampling in several higher-level taxa conducted here, these observations may perhaps be extended to include remaining taxa within their respective groupings.

Nemonychidae (fig. 16)

Although Nemonychidae are known to be at the very base of Curculionoidea , the extant fauna (as with all of the extant weevil groups) appears to show a somewhat derived rostral form. As Dönges (1954) and Lyal (1995) clearly illustrated, a hypothesized weevil ancestor or early weevil linsensus of 3224 most-parsimonious trees, L = 87, CI = 40, RI = 67 (MP trees of L = 59, CI = 59, RI = 85). Unambiguous characters mapped.

Conoderinae Mesoptilinae Cryptorhynchinae Curculioninae exocuticle mesocuticle endocuticle tendon pharynx

C pleurostomal sulcus on the head, including distinctly separate subgenal and occipital sulci. While the study herein examined only one nemonychid representative ( Cimberis pilosa ), its features do not appear as primitive as had been suspected. If one could clearly visualize the head features of more basal genera or some of the extinct nemonychid lineages, it is probable that more primitive features showing closer resemblance to the hypothesized weevil ancestor of the aforementioned authors would be found. In extant Nemonychidae , the plurostomal sulcus is visible in cross section as a somewhat lateral line extending from near the anterior mandibular articulation. The frontal lines also remain, but are not observable in the presented sections. Remnants of the anterior tentorial arms are also visible as a pair of small circles of exocuticle near the dorsolateral corners of the rostrum, just posterior to the mandibles. The subgenal and occipital sulci are separate, though are situated much closer than one might suspect from examinations of the external rostral surface. The pharyngeal plate is robust and strongly sclerotized along the majority of the rostral length.

Anthribidae (figs. 17–18)

Anthribidae show a form similar to that of Nemonychidae , particularly in reference to the position of the occipital and subgenal sulci, though the subgenal sulci appear more reduced in anthribids. The enlarged, bilobed postmentum is a rather striking feature of this family and contributes to the well-developed scaffold formed from the pharyngeal plate and apodemes of the hypostomal-labial sulci, most similar to the condition present in Attelabidae in which these apodemes directly support some of the maxillary tendons. The pleurostomal and frontal sulci are distinct, also extending dorsolaterally in opposite directions as in Nemonychidae , and the pharyngeal plate appears to be rather thin, becoming weakly sclerotized posteriad. The antennae are supported by apodemes located along the dorsolateral corners of the rostral cavity.

Belidae (fig. 19)

The occipital apodemes are present, supsubgenal apodemes appear to have been lost. A peculiar feature of the belid rostrum lies in the arrangement of the mandibular tendons. The adductor tendons nearly always are situated mesally in the rostrum with the abductor tendons more lateral, and positioned along the rostrum according to their point of derivation from the mandible. While the positions of these tendons are normal along the anterior portion of the rostrum, they change posterior to the antennae, where the adductor tendons assume a more lateral position in the apodemes of the occipital sulci. The posterior arms of the pharyngeal plate are simple and rather elongate dorsally, more similar to the condition observed in Nemonychidae than in Anthribidae or Attelabidae . The pleurostomal and frontal sulci also are distinct and extend dorsolaterally. The pharyngeal plate appears to be rather thin and weakly sclerotized.

Attelabidae (figs. 1–7, 20–22)

ATTELABINAE (figs. 20–21): This group possesses separate occipital and subgenal sulci, although the latter (and the associated apodemes) may be indistinct and reduced in short-snouted taxa and may not support the maxillary tendons. As in Anthribidae , the posterior arms of the pharyngeal plate and apodemes of the hypostomal-labial sulci are fairly elaborate and support some of the maxillary tendons. The pleurostomal and frontal sulci are distinct and extend dorsolaterally. The pharyngeal plate is thin anteriorly and appears to become diminished posteriorly at least by the middle of the rostrum.

RHYNCHITINAE (figs. 1–7, 22): This group is similar to Attelabinae , although slightly different in that the occipital and subgenal sulci are distinctly separate and bear well-developed apodemes. While these pairs of sulci remain separate along the length of the rostrum, the lateral extensions of their internal apodemes fuse on each side and form intermittent bridges. The pleurostomal and frontal sulci are distinct and extend dorsolaterally. The pharyngeal plate, similar to its condition in Attelabinae , is short, distinct, and thin anteriorly, becoming weaker posteriorly.

C pleurostomal sulcus

C

D, E mandible F, G

H

I condyle pharyngeal postmentum anterior tentorial arm D postmentum pharynx

F G

ampullar ostium adductor tendon occipital sulcus pharyngeal

M28 circular abductor pharyngeal

subgenal sulcus plate process maxilla D E adductor tendon occipital sulcus abductor tendon posterior arm of pharyngeal plate hypostomal-labial sulcus G F

adductor tendon sulcus maxillary rostrum through mouthparts and proceeding posteriad to proximal area of mouthparts and antennal insertion; H, diagram of G; J, diagram of section just posterior to mouthparts and antennal insertion.

adductor abductor sulcus postmentum sulcus plate M28 G H

adductor occipital subgenal sulcus maxillary tendons posterior to mouthparts and anterior to antennal insertion; G, section near base of rostrum, posterior to antennal insertion; H, diagram of G.

Caridae (fig. 23)

In Caridae , the pleurostomal region extends more ventral than in all other weevils, a feature noticeable by the near ventral insertion of the antennae. Perhaps only the rostrum in Apioninae approaches a similar condition. Likewise, the occipital sulci have migrated ventrally and nearly touch mesally. This character is visible in sections adjacent to the sulci, and the tendons are located fairly closely as well as a result. The pleurostomal sulci are distinct and the frontal sulci extend dorsally. The pharyngeal plate is fairly robust and sclerotized. The posterior arms of the pharyngeal plate (apodemes of the postmentum) form a broad complex in proximity to the anterior arms, thus appearing to form a bridge with the apodemes of the occipital sulci just posterior to the mandibles (as they do in Nemonychidae , Anthribidae , Belidae , and Attelabidae ). Immediately posterior to the postmentum, the apodemes of the hypostomal-labial sulci (essentially extensions of and indistinguishable from those apodemes of the postmentum) are moderately developed, strongly sclerotized, and fused for a short distance at midheight.

Brentidae (figs. 10E, 11A–B, 24–27)

ITHYCERINAE (fig. 24): The middle part of the rostrum in Ithycerinae appears somewhat similar to Nemonychidae in the position of the occipital sulci and mandibular tendons, though it lacks distinct subgenal sulci and the associated apodemes. The pharyngeal plate also does not extend far, ending before midlength of the rostrum. Near the apex, the similarity more resembles the condition in the Brentidae , particularly in the weakly developed posterior arms of the pharyngeal plate. The pleurostomal sulci are distinct and the frontal sulci extend dorsally. A rather unique feature appears to be the position of the occipital sulci and the associated internal apodemes, both situated more dorsally in the rostral cavity than in other weevils.

BRENTINAE (figs. 11A–B, 25): The rostral structure of this group appears quite similar to that in Caridae along the middle portion of the rostrum (largely with respect to apodeme structure and tendon placement), though it differs substantially near the base (adjacent to the antennal insertion) and at the apex (particularly in form and robustness of the posterior arms of the pharyngeal plate). In relation to its diameter, the rostrum in this group possesses a thick cuticle in comparison to those of most weevils, with perhaps the rostrum of some curculionines approaching a similar form and thickness. Nearer to the rostral base, the mandibular adductor tendons assume a slight dorsal position above the abductors. Near the base of the occipital sulci, as they migrate laterally toward the compound eyes at the rostral base, evidence of their position is retained by the presence of their internal apodemes, even though the invagination of any exocuticle diminishes. Also, while the tendons of the antennae appear to usually move rather freely within the rostrum in most weevils, or at least along the sides of the rostral cavity, small cuticular canals (similar to those in some Anthribidae ) are present dorsolaterally in Brentinae to receive these tendons. The pleurostomal sulci are distinct and the frontal sulci extend dorsally. The pharyngeal plate is short and does not extend to midlength of the rostrum.

Other interesting features include the crystalline lens covering the ommatidia (also mentioned by Zimmerman, 1994), apparently a fusion and tremendous thickening of the cuticle of the individual lenses, and the cephalic glands on both sides of the head and immediately anterior to the compound eyes (Zimmerman, 1994). Fresh material unfortunately was not utilized for this taxon, and in the absence of preserved glands, histological detail was not obtained.

APIONINAE (figs. 10E, 26): This group is similar to Brentinae in which the occipital sulci and their apodemes are situated ventrally on the rostrum, though the apodemes are fused medially for nearly the entire length of the rostrum. This fusion of the apodemes is quite distinct and unique near the rostral apex, appearing as a nearly semicircular platform supporting all mandibular and maxillary tendons. Toward the rostral base, the curvature of this apodemal platform lessens. Any modifications for reception of the antennal apodemes do not appear to be present.

I, digram of H.

and slightly anterior to middle of rostrum; F, diagram of E; G, section at base of rostrum and antennal insertion; H, diagram of G; I, section through anterior part of head and eyes; J, section through middle of eyes and head.

parts and anterior to antennal insertion; F, diagram of E; I, diagram of G; H, section near base of rostrum at antennal insertion.

anterior condyle maxilla C frontal sulcus

mandible hypostomal postmentum hypostomal-labial pharyngeal plate abductor tendon adductor tendon occipital sulcus maxillary tendons tized than in Brentinae . The pleurostomal sulci are distinct and frontal sulci extend dorsally.

NANOPHYINAE (fig. 27): While Nanophyinae also maintains some similarity with Brentinae , the occipital sulci and their apodemes are more distanced from each other and positioned at the ventrolateral corners of the rostrum. These apodemes also do not join medially, but remain separate, their form and sequence of supporting the mandibular and maxillary tendons similar to those of many groups basal to and within Curculionidae . The posterior arms of the pharyngeal plate are similar to those of Brentinae in being quite thin and appearing rather frail, though they are apparently fused to form one medial apodeme in this subfamily. The pleurostomal sulci are distinct and the frontal sulci extend dorsally. The pharyngeal plate is thin near the rostral apex, becoming thicker and more strongly sclerotized posterior to the posterior arms, but does not appear to extend beyond midlength, or it is at least indistinct and weakly sclerotized near this area.

Curculionidae (figs. 28–50)

Although the subgenal sulci and apodemes are absent in this family, it perhaps possesses the most diversity in terms of internal rostral structure. The pleurostomal sulci are absent, possibly present only as remnants in the immediate area of the precoila. The frontal sulci are visible in at least Brachycerinae , Bagoinae , Hyperinae , and some Scolytinae . The occipital sulci seem to be similarly positioned ventrally in all curculionid lineages; however, the form of their apodemes varies rather dramatically between subfamilies and appears to remain fairly stable within subfamilies. The posterior arms of the pharyngeal plate are well developed and sclerotized, forming C-shaped supports (in cross section) at their dorsal extensions for the mandibular adductor tendons near the oral orifice and posterior to the mandibles. Probably due to the stronger curvature of the rostrum and not necessarily dependent upon its length, the pharyngeal plate is well sclerotized and extends along most of the length of the rostrum in several curculionid subfamilies; however, it may weaken and become indis-

BRACHYCERINAE (figs. 28–30). Brachycerini (fig. 28): The occipital sulci and apodemes are positioned more laterally and are somewhat elevated from the ventral floor of the rostrum in the Brachycerini . Somewhat similar to Apioninae , the apodemes of the occipital sulci form a broad platform. However, it is unclear whether the individual apodemes completely merge medially or merely touch. The placement of the apodemes and arrangement of the tendons are most similar to the conditions found in Nanophyinae and Raymondionymini. The pleurostomal sulci are distinct and the frontal sulci extend dorsally. The pharyngeal plate is thin but distinct and well sclerotized, extending to the rostral base. A short, wide cavity was found along the dorsal surface of the rostrum between the two distinct layers of endocuticle. It is possible that the cavity resulted from a distortion through desiccation of the specimen.

Raymondionymini (fig. 29): The occipital sulci, their associated apodemes, and mandibular and maxillary tendons are positioned similarly to those in Brachycerini and Erirhinini , although the apodemes are fairly short and do not approximate one another medially, a condition more similar to that in the latter lineage than the former. The posterior arms of the pharyngeal plate are weakly developed near the rostral apex, similar to those in Nanophyinae in which they fuse medially and form an elongated stalk ventral to the pharynx. Slightly posteriad they become separated by a thin medial bridge, then gradually become thicker and more robust before disappearing. Posterior to the hypostomal-labial sulci and toward the middle of the rostrum, the pharyngeal plate is thin and weakly sclerotized and does not appear to surpass midlength of the rostrum. The pleurostomal sulci are distinct and the frontal sulci extend dorsally.

Erirhinini (fig. 30): This tribe is similar to Raymondionymini, possessing more laterally positioned occipital sulci with short and separated apodemes. The apodemes, however, become slightly more elongated near the rostral base, but they do not merge medially. The arrangement of the maxillary tendons approximates that of arms of the pharyngeal plate are similar to those of Raymondionymini and Bagoinae , although perhaps more like the latter in the more robust form of the apodemes and fusion at the middle. The pleurostomal sulci are distinct and the frontal sulci extend dorsally. The pharyngeal plate is thin but distinct and moderately sclerotized.

DRYOPHTHORINAE (figs. 11C, 31–32): Continuing throughout the Curculionidae , the number and position of sulci remain moderately stable, and the pleurostomal and frontal sulci are indistinct (excepting the lineages noted above). In this group, the pharyngeal plate is well sclerotized with exocuticle, wide, distinct, and extends to the rostral base. The posterior arms of the pharyngeal plate are well developed and sclerotized, fused medially and forming a slender stalk. In cross section, these apodemes also form slightly distorted C-shaped supports at their dorsal extensions for the mandibular adductor tendons near the oral orifice and posterior to the mandibles. As the occipital sulci are positioned more ventrolaterally, the mandibular abductor tendons are held more dorsal to the adductors and maxillary tendons.

PLATYPODINAE (figs. 9, 33): This group superficially appears similar to Scolytinae in internal rostral structure, and to Ithycerus in terms of the general structure of the rostral apex in particular. The subgenal sulci are evident both externally and internally, forming moderately long apodemes internally that fuse near the paracoila, though the occipital sulci are rather indistinct. While there seems to be a faint line of exocuticle near the dorsal mandibular articulation, distinct pleurostomal and frontal sulci are not evident. As in Scolytinae , the hypostomal sinus is slightly internalized, though to a lesser degree. The pharyngeal plate is thin and sclerotized and the posterior arms of the pharyngeal plate are thin and closely situated, a condition present in only one anterior to antennal insertion; F, section at antennal insertion, posterior to mouthparts; G, section at middle of rostrum; H, diagram of section near base of rostrum.

immediately posterior to mouthparts; G, section posterior to mouthparts at antennal insertion; H, section posterior to antennal insertion at middle of rostrum; I, section near base of rostrum; J, diagram of section from I.

gram of E; G, section near middle of head, posterior to antennal insertion and anterior to eyes. other lineage, Dryophthorinae . Different from the condition in Scolytinae , the maxilla extends further into the head and the cardo articulates at the merged junction of the postmentum and apodemes of the subgenal sulci.

BAGOINAE (fig. 34): Along with Hyperinae , this group is closest to the remaining Curculionidae (fig. 13), but possesses distinct, dorsally extending frontal sulci. The cuticle is comparatively thin, similar to that in Mesoptilinae, Conoderinae , and many Entiminae . The apodemes of the occipital sulci are fairly elevated above the ventral floor of the rostrum, at least partially due to the relatively thin cuticle, and they merge medially. The posterior arms of the pharyngeal plate are similar to those in many other curculionids, rather robust, fusing and forming a bridge medially, and their dorsal extensions forming distinct C-shaped supports. A peculiar feature is the large size of the pharynx beginning around the middle of the rostrum, in which it extends to the inner dorsal surface of the rostrum, causing the pharyngeal dilator muscles to be greatly shortened.

HYPERINAE (fig. 35): Hyperinae is quite similar to Lixinae, as well as to Molytinae , differing mostly from the former in not possessing a strong basal constriction of the rostrum, which causes the apodemes of the occipital sulci to approach one another, such that they become positioned on the ventral floor of the rostrum (not elevated). As in the previous two subfamilies, the pharyngeal plate is short and weakly sclerotized, ending before the antennal insertion. The posterior arms of the pharyngeal plate also are robust, separated at their distal extensions along the rostrum, then fusing medially. Contrasting to Bagoinae , the frontal sulci are indistinct.

ENTIMINAE (figs. 10D, 11D–F, 36): Although members of Entiminae often possess a shortened rostrum, its structure is akin to that of Conoderinae and Bagoinae , in which the apodemes of the occipital sulci are slightly elevated from the ventral floor of the rostrum; in taxa bearing a longer rostrum, the mandibular adductor tendons also rest on these apodemes (fig. 36H). A major difference is that the posterior arms of the pharyngeal and are less robust. In those taxa with a short rostrum, the apodemes of the occipital sulci appear to stratify horizontally, with the mandibular abductor tendons situated laterally to those of the adductors. In longer rostrate taxa, the apodemal arrangement matches that in Cyclominae , in which they are stratified vertically and the mandibular adductor tendons situated dorsal to the abductors. The pharyngeal plate is short but distinct, appearing to extend at least beyond the antennal insertion and to nearly midlength of the rostrum. Interestingly, apodemes for supporting the antennal tendons are present in Entiminae , located along the dorsolateral corners in the rostral cavity. From this study, it appears that this subfamily is unique in possessing these antennal supports within Curculionidae . This feature was also found to be present in Brentinae ( Brentidae ) and Anthribidae .

CYCLOMINAE (figs. 10A–B, 37): As the occipital sulci are positioned more ventrolaterally in this group, the apodemes do not merge medially but do approach one another toward the rostral base. The mandibular adductor tendons are held dorsally, while the abductor tendons are immediately ventral, enclosed in a tunnel formed by the apodemes. The pharyngeal plate is distinct and strongly sclerotized, extending a short distance near the rostral apex and ending before the antennal insertion. The posterior arms of the pharyngeal plate are robust and only narrowly attach medially at two points to form the plate (figs. 10A–B). The form of the pharynx may also be noted, becoming large and circular near the rostral base.

MOLYTINAE (figs. 10F, 38): Molytinae display a fairly typical sulcus and tendon orientation, in which the occipital sulci are adjacent to the lateral corners of the rostrum and their apodemes short, separated, and resting on the ventral floor of the rostrum. The mandibular adductor tendons are located mesal and slightly dorsal to the abductor tendons. The pharyngeal plate is distinct and strongly developed, mostly visible near the rostral apex due to the short extension of the medial part of the plate, and is absent posterior to the antennal insertion. The posterior arms of abductor tendon mouthparts, immediately posterior to antennal insertion; E, diagram of D; F, section at base of rostrum; G, diagram of F; H, Diaprepes abbreviatus ( Curculionidae : Entiminae ), section at middle of pupal rostrum. parts; F, section posterior to antennal insertion, anterior to middle of rostrum; G, section slightly posterior to middle of rostrum; H, diagram of section at middle of rostrum.

rated at their distal extensions along the rostrum, then fusing medially and forming a thickened platform at the pharyngeal plate posterior to the endpoint of the hypostomal-labial sulci.

COSSONINAE (fig. 39): Cossoninae is fairly similar to Cyclominae and Cryptorhynchinae with vertically stratified apodemes. It is perhaps most alike to Baridinae, however, by the more proximal occipital sulci which allow for the medial fusion of the apodemes. These apodemes also have elongate apical extensions, although they are not so appressed to the inner rostral wall as in Baridinae. The posterior arms of the pharyngeal plate also fuse medially and are robust. The pharyngeal plate is distinct and sclerotized for only a short distance, extending approximately until the antennal insertion.

SCOLYTINAE (figs. 40–42). Xyleborini (figs. 40–41): As the rostrum in the extant members of this group is more or less absent, supposedly diminished from a fully rostrate ancestor with only remnants present in some taxa, much information has been lost in terms of sulci and tendon position, as well as degree of apodeme development. Internally the rostrum appears deceptively simplified and similar to a chrysomelid, in which the tendons no longer require supporting apodemes to facilitate movement and reduce damage. The occipital sulci, therefore, are fairly short (as observed by Lyal, 1995), their apodemes also short and appressed along the rostrum wall. The frontal sulci appear to be faintly present in this subfamily, though are suspected to be largely obliterated in most of the lineage. Due to the compaction of the head and rostrum, the pharyngeal plate appears to have been lost, but there are distinct remnants of the anterior and posterior arms. The postmentum and hypostomal sinus (into which the maxillae are positioned) are reduced and have become more internalized. The apodemes of the postmentum and hypostomal-labial sulci remain, though the internalization of the hypostomal sinus has slightly displaced and changed the typical form of these apodemes as they are seen in other weevils. The pharyngeal plate appears to be absent. The anterior arms are present and the articulation of the prementum. The maxillary cardo completely articulates with the postmental apodemes, whereas it jointly articulates at the base of the hypostomal sinus (paracoila) and fusion of the posterior arms of the pharyngeal plate in all other weevils. While not supporting any tendons, the apodemes of the subgenal sulci form a large internal ridge (these internal apodemes are also illustrated in Lyal, 1995).

Hylastini (fig. 42): Hylastini is thought to be more of a basal group within this subfamily and, in accordance with this hypothesis, the sections reveal that indeed has more primitive features. As the subgenal sulci are visible externally and their apodemes developed internally in Xyleborini , they are comparatively more distinct in Hylastini . The apodemes of the occipital sulci are slightly more developed and not as appressed to the rostrum wall. The frontal sulci also are distinct, appearing to extend dorsally as in other families and curculionid subfamilies intermediate in weevil phylogeny. The occipital sulci are fairly distinct and form abbreviated apodemes supporting the mandibular abductor tendons. As in Xyleborini , the pharyngeal plate appears to have been lost or highly reduced and weakly sclerotized.

LIXINAE (fig. 43): This group is fairly similar to Molytinae , although the apodemes of the occipital sulci hold the tendons slightly more elevated from the ventral floor of the rostrum. The posterior arms of the pharyngeal plate also are robust, initially separated at their distal extensions along the rostrum, then fusing medially. The occipital sulci are fairly visible externally in Lixinae. Toward the rostral base, the apodemes nearly merge medially due to constriction caused by the antennal scrobe. The pharyngeal plate is weakly developed and appears to end before the antennal insertion.

BARIDINAE (fig. 44): Baridinae and a few other subfamilies have evolved more derived and elaborate apodemal complexes for holding the mouthpart tendons. The occipital sulci are positioned rather closely and ventrally, while the apodemes have formed a tiered structure caused by the medioventral migration of the mandibular abductor tendons and their associated apodemes under to mouthparts, near antennal insertion; F, section near middle of rostrum, posterior to antennal insertion; G, diagram of E; H, section near base of rostrum; I, diagram of H.

hypostomal of pharyngeal sulcus paracoila hypostomalsulcus plate labial sulcus mandibular

F G

occipital sulcus sulcus mandibular hypostomal-labial sulcus esophagus mandibular adductor mandibular abductor mouthparts at antennal insertion; E, section immediately posterior to mouthparts and through middle of eyes; F, diagram of D; G, diagram of E; H, section through posterior of eyes and near middle of head.

antennal insertion, through mouthparts and anterior of eyes; G, section at proximal area of mouthparts, posterior to antennal insertion; H, section at middle of head and posterior of eyes; I, section just posterior to middle of head.

mouthparts; F, G, I, sections posterior to mouthparts and antennal insertion, anterior to eyes; H, diagram of F; J, section immediately anterior of eyes.

insertion; E, diagram of D; F, section at middle of rostrum, posterior to antennal insertion; G, diagram of F; H, section near base of rostrum, showing ventral portion.

A D C E, F G, H

C

F adductor tendon posterior arm pharyngeal plate hypostomalsulcus abductor pharyngeal circular tendon muscles pharyngeal plate adductor tendon abductor tendon occipital sulcus antennal insertion; F, diagram of E; G, section posterior to middle of rostrum and antennal insertion; H, diagram of G.

apodemes. The resulting structure is akin to a ventral tunnel through which the mandibular abductor tendons pass, and a dorsal platform supporting the mandibular adductors on the sides and the maxillary tendons in the middle. The posterior arms of the pharyngeal plate are fairly typical, namely moderately robust, separated along their apical extensions in the rostrum at the hypostomal sinus and fusing medially along their posterior extensions. The pharyngeal plate is rather well sclerotized and extends most of the length of the rostrum.

CONODERINAE (fig. 45): The structure of the apodemes and position of the occipital sulci along much of the rostrum in Conoderinae is nearly identical to Bagoinae , in which the apodemes form a platform elevated above the ventral floor of the rostrum (again perhaps at least partially due to the thin rostral cuticle). The major difference lies in a slight alteration in the arrangement of maxillary tendons. Also, as in the former few subfamilies (e.g., Cossoninae , Cryptorhynchinae, Molytinae , Lixinae), the posterior arms of the pharyngeal plate fuse medially. The pharyngeal plate is distinct, sclerotized, and moderately long, ending just before the antennal insertion.

CRYPTORHYNCHINAE (figs. 10C, 46): This subfamily appears nearly identical to Cyclominae , in which the apodemes and tendons are vertically stratified at the lateral corners of the rostrum. Near the rostral apex, however, the posterior arms of the pharyngeal plate fuse medially, forming an X-shaped scaffold as in Molytinae and Lixinae. The pharyngeal plate also is well sclerotized, extending most of the length of the rostrum and ending near the rostral base. Other interesting features include the elongate apical extensions of the apodemes of the occipital sulci, which fuse distally and extend along the inner lateral surface of the rostrum. The maxillary tendons also are particularly enlarged, nearing the size of the mandibular abductor tendon.

MESOPTILINAE (fig. 47): This family displays another distinct vertical stratification of the apodemes of the occipital sulci, similar to that present in Cossoninae , in which there is a short medial bridge linking the apodemes of the two occipital sulci. The apical extensions of these apodemes are basally divergent and separated from the lateral wall of the rostrum and apically merging with it. The medial fusion of the posterior arms of the pharyngeal plate is also present, though the apodemes are less robust and the C-shaped support for the anterior portions of the mandibular adductor tendons is diminished and weakly sclerotized. The pharyngeal plate is weakly developed and short, ending before the antennal insertion. The mandibular adductor tendons, as well as those of the abductor, are rather enlarged and oblong, a condition similar (though less extreme) to that found in Cyclominae , Cryptorhynchinae, Bagoinae , and perhaps also Cossoninae .

CEUTORHYNCHINAE (fig. 48): The internal rostrum structure in this group is remarkably similar along the entire length to that in Molytinae and Hyperinae . The occipital sulci are positioned ventromedially (as opposed to more ventrolateral as in the former two subfamilies) and are more close together, such as in Baridinae, in which the mandibular adductor tendons are situated mesal to the abductors. The posterior arms of the pharyngeal plate are robust, slightly less so more apically along the rostrum, and appear to remain separate, although the medial portions of the apodemes approach one another quite closely along the hypostomal sinus. The pharyngeal plate is distinct and sclerotized, extending most of the length of the rostrum and ending near the rostral base.

CURCULIONINAE (figs. 49–50): This group perhaps appears most similar to Ceutorhynchinae , particularly in the arrangement of the mandibular and maxillary tendons. The posterior arms of the pharyngeal plate, although distinct, are less robust and slender, fused and stalked medially. The pharyngeal plate appears distinct, well sclerotized, and fairly long, extending just beyond the antennal insertion and ending thereafter. The apodemes of the occipital sulci are ventral, approaching one another medially toward the base of the rostrum, and they seem to at least partially merge medially in some taxa. In Curculio , due to the lateral rotation of the mandibular articulations and almost vertical movement of the mandibles, the mandibular abductor tendons are larger and more robust than those of the adductors.

gram of D; F, section posterior to mouthparts, anterior to antennal insertion; G, diagram of F; H, section near base of rostrum and antennal insertion, showing ventral portion of section.

antennal insertion; E, diagram of D; F, section at base of rostrum, posterior to antennal insertion; G, diagram of F; H, section at base of rostrum, showing ventral portion of section.

posterior to mouthparts, anterior to antennal insertion; F, diagram of E; G, section posterior to middle of rostrum and antennal insertion; H, diagram of G.

section posterior to mouthparts, anterior to antennal insertion; F, diagram of E; G, section near base of rostrum, posterior to antennal insertion; H, diagram of G.