Anchylorhynchus Variabilis

''Anchylorhynchus'' is a genus of weevils belonging the family Curculionidae and subfamily Curculioninae. It currently includes 25 described species distributed from Panama to Argentina. Members of the genus are pollinators of palms in the genera '' Syagrus'', ''Oenocarpus'' and ''Butia'', with adults living in inflorescences and larvae feeding on developing fruits. The first instar larvae of ''Anchylorhynchus'' have an unusual morphology, being specialized on killing other larvae infesting the palm fruits.

Adult morphology

''Anchylorhynchus'' can be readily distinguished from other Derelomini by a number of features. The body is round, convex, and densely covered by scales varying from yellow to black. The rostrum is flattened dorso-verntrally at the apex, and exhibits 2-7 longitudinal grooves from the base of the rostrum to the insertion of antennae. The antennal funicle (segments excluding the first and the club) has only six segments, as opposed to seven segments in other genera. The antennae are inserted at the apex of the rostrum in both sexes, while it is inserted closer to the base in most other Curculionidae (at least in females).

Species of ''Anchylorhynchus'' are sexually dimorphic, with males usually being larger than females. In some species, males also have longer tarsi, and/or denser and longer hairs in the ventrites, metasternum and tarsi. In all described species, females have a retraction in ventrites III-IV of the abdomen. The shape and degree of retraction varies between species, but these segments are always flat in males.

Anchylorhynchus vanini female dorsal.png, ''A. vanini'', female, dorsal
Anchylorhynchus vanini female ventral.png, ''A. vanini'', female, ventral
Color variation in Anchylorhynchus eriospathae.png, Color polymorphism in ''A. eriospathae''

Larval morphology and behavior

Larvae of ''Anchylorhynchus'' go through 4 stages (instars) before molting into a pupa.
The most distinctive stage is the first instar. First-instar larvae of ''Anchylorhynchus'' are unique in Curculionidae due to their falcate mandibles (usually found in insects that feed on other insects). Additionally, they are flattened dorso-ventrally, living between sepals and petals of female palm flowers. After hatching, larvae migrate to the base of the female flower, drilling a hole into the developing fruit. After entering the fruit, larvae molt and start consuming plant tissues, causing abortion of developing fruits. First- and second instar larvae attack and consume other larvae upon encountering them. Later instars avoid other larvae and are not aggressive.
Starting on the second instar, larvae acquire the grub-like, cylindrical and C-shaped body characteristic of other Curculionidae. The mandible also changes its shape, becoming triangular and broad, adapted to crush plant tissues.

First instar larva of Anchylorhynchus eriospathae.png, First-instar larva
Fourth instar larva of Anchylorhynchus eriospathae.png, Fourth-instar larva

Interaction with plants

Adults ''Anchylorhynchus'' visit male and female flowers of several palm species in the genera '' Syagrus'', ''Oenocarpus'' and ''Butia''. ''Anchylorhynchus minimus'' might be associated with ''Euterpe edulis'', but this is still unconfirmed. Adults use their rostrum to open male flowers and feed on pollen. While resting, they remain in the branches of the inflorescence or hidden at its base. Unlike most Curculionidae, females do not use the rostrum to drill an oviposition hole in plant tissues. Instead, they lay eggs directly between petals and sepals of female flowers.

The first observation about natural history of ''Anchylorhynchus'' was published by Faust, who described ''A. burmeisteri'' from specimens collected from palms in Argentina. Gregório Bondar made most of the subsequent observations, recording host plants for many species. He considered ''A. trapezicollis'' to be a pest of the palm known as licuri (''Syagrus coronata''). He observed that adults fed on pollen and conjectured that larvae might feed on flowers, even though he never observed them. More recently, the full life cycle of ''A. eriospathae'' has been described, showing that larvae feed on developing seeds and adults on pollen. Also, species of ''Anchylorhynchus'' have been shown to be important pollinators of ''Oenocarpus bataua'', ''Oenocarpus balickii'', ''Oenocarpus minor'', '' Butia paraguayensis'' and ''Syagrus loefgrenii''.

Taxonomy

There are currently 25 valid species of ''Anchylorhynchus''.

The following list shows all valid species, with recognized synonyms shown indented:

* ''Anchylorhynchus aegrotus'' FÃ¥hraeus, 1843
* ''Anchylorhynchus albidus'' Bondar, 1943
* ''Anchylorhynchus amazonicus'' Voss, 1943
* ''Anchylorhynchus bicarinatus'' O'Brien, 1981
** ''Anchylorhynchus gottsbergerorum'' Vanin, 1995
* ''Anchylorhynchus bicolor'' Voss, 1943
** ''Anchylorhynchus leiospathae'' Bondar, 1950
* ''Anchylorhynchus bucki'' Vanin, 1973
* ''Anchylorhynchus burmeisteri'' Faust, 1894
* ''Anchylorhynchus camposi'' Bondar, 1941
* ''Anchylorhynchus centrosquamatus'' de Medeiros & Núñez-Avellaneda, 2013
* ''Anchylorhynchus chrysomeloides'' de Medeiros & Vanin, 2020
* ''Anchylorhynchus goiano'' de Medeiros & Vanin, 2020
* ''Anchylorhynchus imitator'' de Medeiros & Vanin, 2020
* ''Anchylorhynchus latipes'' de Medeiros & Vanin, 2020
* ''Anchylorhynchus luteobrunneus'' de Medeiros & Núñez-Avellaneda, 2013
* ''Anchylorhynchus minimus'' Bondar, 1950
* ''Anchylorhynchus multisquamis'' de Medeiros & Vanin, 2020
* ''Anchylorhynchus parcus'' FÃ¥hraeus, 1843
* ''Anchylorhynchus pinocchio'' de Medeiros & Núñez-Avellaneda, 2013
* ''Anchylorhynchus rectus'' de Medeiros & Vanin, 2020
* ''Anchylorhynchus trapezicollis'' Hustache, 1940
** ''Anchylorhynchus bleyi'' Bondar, 1941
** ''Anchylorhynchus botryophorae'' Bondar, 1941
* ''Anchylorhynchus tremolerasi'' Hustache, 1937
** ''Anchylorhynchus eriospathae'' Bondar, 1943
** ''Anchylorhynchus hatschbachi'' Bondar, 1943
** ''Anchylorhynchus pictipennis'' Hustache, 1937
* ''Anchylorhynchus tricarinatus'' Vaurie, 1954
* ''Anchylorhynchus vanini'' Valente & de Medeiros, 2013
* ''Anchylorhynchus variabilis'' Gyllenhaal, 1836
** ''Anchylorhynchus mutabilis'' FÃ¥hraeus, 1843
***''Anchylorhynchus mutabilis connata'' Voss, 1943
* ''Anchylorhynchus vittipennis'' Voss, 1943
** ''Anchylorhynchus nigripennis'' Voss, 1943
** ''Anchylorhynchus lineatus'' Bondar, 1943

References

{{Taxonbar, from=Q14925232

Curculioninae
Beetles described in 1836
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Beetles of South America