Tetraonyx fulvus, copyright Fydnar.

Belongs within: Meloinae.

American hitch-hikers
Published 11 June 2024

One of the major sticking points in the classification of the Meloidae, the blister beetles, has been the question of what to make of the Tetraonycini. This distinctive assemblage of blister beetles is unique to the Americas, and exhibits a number of features that stand out within the family.

Tetraonyx sexguttatus, copyright Hugo Neves Martinho.

Members of the Tetraonycini are distinguished by tarsi on the fore legs with the segments bilobed and padded underneath. The claws are divided between free, subequal dorsal and ventral blades, with the undersides of the blades being smooth (Pinto & Bologna 2002—hence, of course, the name ‘Tetraonyx‘ meaning ‘four claws’). Tetraonycins start their lives as kleptoparasites of bees, with first instar larvae reaching host nests by phoresy. In most species, eggs are laid on vegetation and the phoretic larvae climb onto visiting hosts after hatching, but in some species the eggs are laid in the bee nests themselves.

Meloetyphlus fuscatus, copyright el-insectarium.

The majority of tetraonycins are assigned to a single genus Tetraonyx, widespread across North and South America. Only two South American species are each assigned to their own monotypic genus, Opiomeloe flavipennis and Meloetyphlus fuscatus (Selander 1985). Both these species are flightless, with more or less reduced elytra and hind wings (much more so in Meloetyphlus than Opiomeloe). Meloetyphlus fuscatus is a parasite of orchid bees; the hosts of O. flavipennis do not appear to be clearly established but the collector of the original type specimens suggested an association with bumble bees. Opiomeloe flavipennis has the eyes somewhat reduced in size compared to Tetraonyx whereas M. fuscatus is completely blind. In both species, adults are thought not to feed but mandibles are enlarged, seemingly used for some other purpose such as intra-specific conflict or digging in the walls of the host nests. Whereas the flighted Tetraonyx lay their eggs on vegetation, the two flightless species lay eggs in the host nest, with larvae being carried by young host individuals emerging to establish their own colonies. In this way, they need never be forced to make their own way in the world.

Systematics of Tetraonycini
Tetraonycini [Tetraonycinae]
`--Tetraonyx Latreille 1805 [incl. Iodema Pascoe 1862, Jodema Gemminger & Harold 1870]PB02
|--T. bicolorLC40
|--T. bimaculatus [incl. T. quadrimaculatum]LC40
|--T. bipunctataLC40
|--T. collarisLC40
|--T. cruciatus Laporte de Castelnau 1840LC40
|--T. cubensisB90
|--T. femoratus Laporte de Castelnau 1840LC40
|--T. frontalisI92
|--T. fulvusK63
|--T. limbatus Laporte de Castelnau 1840LC40
|--T. maculatus Laporte de Castelnau 1840LC40
|--T. octomaculatusLC40
|--T. quadrimaculatus Fab. 1792FS90 [incl. T. cruciatusB90]
|--T. rupicollis Laporte de Castelnau 1840LC40
|--T. sexguttatusLC40
`--T. ventralisLC40

*Type species of generic name indicated


[B90] Beauregard, M. 1890. Notes synonymiques suivantes relativement à quelques espèces de la tribu des vésicants. Annales de la Société Entomologique de France, 6e série 9: ccxii–ccxiii.

[FS90] Fleutiaux, E., & A. Sallé. 1890. Liste des coléoptères de la Guadeloupe et descriptions d’espèces nouvelles. Annales de la Société Entomologique de France, 6e série 9: 351–484.

[I92] Imes, R. 1992. The Practical Entomologist. Aurum Press: London.

[K63] Kaszab, Z. 1963. Merkmale der Adaptation, Spezialisation, Konvergenz, Korrelation und Progression bei den Meloiden (Coleoptera). Acta Zoologica Academiae Scientiarum Hungaricae 9 (1–2): 135–175.

[LC40] Laporte de Castelnau, F. 1840. Histoire Naturelle des Insectes Coléoptères vol. 2. P. Duménil: Paris.

[PB02] Pinto, J. D., & M. A. Bologna. 2002. Meloidae Gyllenhal 1810. In: Arnett, R. H., Jr, M. C. Thomas, P. E. Skelley & J. H. Frank (eds) American Beetles vol. 2. Polyphaga: Scarabaeoidea through Curculionoidea pp. 522–529. CRC Press.

Selander, R. B. 1985. A new genus of blister beetles linking Meloetyphlus with Tetraonyx (Coleoptera: Meloidae). Journal of the Kansas Entomological Society 58 (4): 611–619.

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