Melanterius

Melanterius pungalinae, from Pinzón-Navarro et al. (2017).

Belongs within: Cleogonini.

Melanterius is an Australasian genus of weevils that mostly attack the developing seeds of Acacia species. Exemplars have the pronotum finely punctate and the prosternum excavated to receive the rostrum (Pinzón-Navarro et al. 2017).

Melanterius weevils
Published 17 July 2022

Here in the Antipodes, we have a long history of environmental upheaval from exotic taxa unwisely released. As a result, one can’t help but feel an odd twinge of perverse patriotism when hearing of the inverse, some native of the Antipodes causing grief elsewhere. In South Africa, Australian acacias have become something of an issue, inciting a search for potential control agents. Among the candidates selected are weevils of the genus Melanterius.

Melanterius servulus, copyright Sally Adam.

Melanterius is a diverse genus of small black or brown weevils (ranging from about three to seven millimetres in length) that feed as both adults and larvae on the developing seeds of acacias. About eighty species have been recognised in the genus to date and possibly many more remain to be described. In general, Melanterius weevils are heavily punctate, usually without prominent hairs but with a covering of scales. The rostrum is reasonably long, reaching more or less back to the mesosternum at rest but not sitting in a distinct ventral groove, and may be variably curved (going by figures in Zimmerman 1992).

Melanterius semiporcatus, copyright Victor W. Fazio III.

As with other weevils, the prominent rostrum is used by females to chew into an appropriate spot on the host plant, in this case chewing holes into the developing acacia seed pods, into which eggs are laid. Melanterius species go through one generation per year. Larvae burrow into and feed on the developing seeds before emerging and dropping to the ground to pupate in the soil. Mature adults emerge well before the host acacias begin to set seeds, usually having to wait about six months (Auld 1989). They usually spend the intervening period largely inactive, sheltering in concealed places close to the host plant and occasionally emerging to briefly feed on developing buds.

Under peak conditions, Melanterius infestations may cause a complete failure of seed production. No wonder, then, that they have been considered a worthwhile instrument of biological control.

Systematics of Melanterius

Characters (from Pinzón-Navarro et al. 2017): Shape small, compact; colour brown to black, integument usually mostly bare but on pronotum and elytra with sparse small fine setae or rows or clusters of larger, ferruginous scales, rarely densely squamose; underside and legs somewhat more densely setose or squamose. Rostrum stout, subcylindrical, downcurved, retractable onto venter and there reaching metaventrite, longer and slenderer in female. Head with eyes slightly convex but not protuberant; ventrally not contiguous, there separated by width of rostrum at base. Antennae inserted in about apical third of rostrum in males, in middle in females; with scape folding into sharply delineated scrobe and not quite reaching eye in repose. Pronotum finely regularly punctate; prothorax laterally extended anteriad into ocular lobes covering eyes in repose. Prosternum excavate for receiving rostrum in repose; channel formed anteriorly by precoxal flanges (sometimes with “peep-hole”), medially by usually separate, mesally flattened and ventrally edged procoxae and posteriorly by flattened to concave or saddle-shaped median process of mesoventrite with small to large lateral flanges or butts, open posteriorly (not forming closed receptacle). Elytra with nine complete striae and abbreviated tenth (terminating before apex of metanepisternum), dorsal striae usually deep with large, narrow, confluent or subconfluent punctures, occasionally with very large, round and open punctures; interstriae usually costate to carinate to some degree, sometimes only odd ones, rarely flat. Metanepisternal sutures with row of fine sclerolepidia. Metaventrite with flattened to concave disc, laterally (between meso- and metacoxae) delimitated by blunt edge to sharp carina. Abdominal ventrites 1 and 2 enlarged, each often as long as 3+4, suture between them fused but distinct and complete; 1 usually slightly concave in male but convex in female; 5 usually with large, transverse, shallow median fovea in both sexes. Femora slightly flattened and medially inflated, with ventral tooth at about apical third and often with slight shallow groove on underside for reception of tibiae; tibiae narrowly subcylindrical, uncinate, uncus usually extending into apical flange (false corbel) with flat outer (upper) lobe, uncus in females occasionally arising from outer (upper) angle of tibial apex; setal comb usually long and oblique; tarsal claws fine, simple, divergent. Aedeagus with penis short and broad to elongate and narrow, flat, more or less downcurved; temones long and slender; endophallus usually with apical and basal pairs of small sclerites, sometimes without sclerites; tegmen narrow, with long slender parameres and short broad manubrium; gonocoxites usually elongate, narrow, with large, sometimes broad and flat, apical styli, sometimes membranous without styli; spermatheca weakly sclerotised, of subequal width throughout, often with ramus differentiated and large gland with short, sclerotised duct.

Melanterius Erichson 1842 [incl. Chaleponotus Casey 1892, Melanteriosoma Lea 1899]P-NJO17
| i. s.: M. carinicollis Pascoe 1875M86
| M. cinnamomeus Pascoe 1872M86
| M. floridus Pascoe 1875M86
| M. fugitivus Pascoe 1875M86
|--M. porcatus groupP-NJO17
| |--*M. porcatus Erichson 1842M94
| |--M. bidentatus Lea 1899P-NJO17
| |--M. conspiciendus Lea 1909P-NJO17
| |--M. leptorrhynchus Lea 1911P-NJO17
| |--M. semiporcatus Erichson 1842P-NJO17
| `--M. unidentatus Lea 1899P-NJO17
|--M. costatus groupP-NJO17
| |--M. aberrans Lea 1899P-NJO17
| |--M. arenaceus Lea 1928P-NJO17
| |--M. costatus (Lea 1899) [=*Melanteriosoma costatum; incl. Melanterius uniseriatus Lea 1899]P-NJO17
| |--M. costipennis Lea 1905P-NJO17
| |--M. inconspicuus (Lea 1899) [=Melanteriosoma inconspicuum]P-NJO17
| |--M. lamellatus Lea 1913P-NJO17
| |--M. psittacoides Pinzón-Navarro, Jennings & Oberprieler 2017P-NJO17
| |--M. pungalinae Pinzón-Navarro, Jennings & Oberprieler 2017P-NJO17
| |--M. rufus Lea 1928P-NJO17
| |--M. squamipennis Lea 1928P-NJO17
| |--M. tasmaniensis (Lea 1909) [=Melanteriosoma costatum var. tasmaniense]P-NJO17
| |--M. tibialis Lea 1928P-NJO17
| `--M. vinosus Pascoe 1872P-NJO17
|--M. laticornis groupP-NJO17
| |--M. atronitens Lea 1931P-NJO17
| |--M. compositus Lea 1909P-NJO17
| |--M. corosus (Boisduval 1835) (see below for synonymy)P-NJO17
| |--M. laticornis Lea 1913P-NJO17
| |--M. mediocris Lea 1913P-NJO17
| |--M. persimilis Lea 1909P-NJO17
| |--M. porosus Lea 1899P-NJO17
| |--M. strabonus Lea 1899P-NJO17
| `--M. vulgivagus Lea 1899P-NJO17
|--M. latipennis groupP-NJO17
| |--M. abbreviatus Pinzón-Navarro, Jennings & Oberprieler 2017P-NJO17
| |--M. aratus Pascoe 1885P-NJO17
| |--M. baridioides Lea 1913P-NJO17
| |--M. bicalcaratus Lea 1913P-NJO17
| |--M. curvistriatus Pinzón-Navarro, Jennings & Oberprieler 2017P-NJO17
| |--M. elusus (Casey 1892)P-NJO17 [=*Chaleponotus elususA08; incl. M. pectoralis Lea 1899A08, M. rufimanus Lea 1915P-NJO17]
| |--M. interstitialis Lea 1899P-NJO17
| |--M. latipennis Lea 1928P-NJO17
| |--M. legitimus Lea 1909P-NJO17
| |--M. maestus Lea 1913P-NJO17
| |--M. oleosus Lea 1928P-NJO17
| |--M. semiporosus Lea 1908P-NJO17
| |--M. solitus Lea 1899P-NJO17
| `--M. tesseymani Pinzón-Navarro, Jennings & Oberprieler 2017P-NJO17
|--M. maculatus groupP-NJO17
| |--M. acaciae Lea 1899 [incl. M. caledonicus Lea 1928]P-NJO17
| |--M. antennalis Lea 1899P-NJO17
| |--M. castaneus Lea 1899 [incl. M. compactus Lea 1899]P-NJO17
| |--M. ellipticus Lea 1913P-NJO17
| |--M. fasciculatus Lea 1913P-NJO17
| |--M. maculatus Lea 1899M94
| |--M. servulus Pascoe 1872P-NJO17
| `--M. submaculatus Lea 1928P-NJO17
`--M. ventralis groupP-NJO17
|--M. cardiopterus Lea 1913P-NJO17
|--M. parvidens Lea 1899P-NJO17
`--M. ventralis Lea 1899P-NJO17

Melanterius corosus (Boisduval 1835) [=Cryptorhynchus corosus; incl. M. adipatus Lea 1899, M. piceirostris Erichson 1842]P-NJO17

*Type species of generic name indicated

References

[A08] Anderson, R. S. 2008. The identity of Chaleponotus elusus Casey 1892 (Curculionidae: Molytinae: Conotrachelini). Coleopterists Bulletin 62 (1): 42–44.

Auld, T. D. 1989. Larval survival in the soil and adult emergence in Melanterius Erichson and Plaesiorhinus Blackburn (Coleoptera: Curculionidae) following seed feeding on Acacia and Bossiaea (Fabaceae). Journal of the Australian Entomological Society 28: 235–238.

[M86] Masters, G. 1886. Catalogue of the described Coleoptera of Australia. Part V. Proceedings of the Linnean Society of New South Wales, series 2, 1 (3): 585–686.

[M94] May, B. M. 1994. An introduction to the immature stages of Australian Curculionoidea. In: Zimmerman, E. C. Australian Weevils (Coleoptera: Curculionoidea) vol. 2. Brentidae, Eurhynchidae, Apionidae and a chapter on immature stages by Brenda May pp. 365–728. CSIRO Australia.

[P-NJO17] Pinzón-Navarro, S. V., D. Jennings & R. G. Oberprieler. 2017. Host associations of Melanterius Erichson (Coleoptera: Curculionidae: Cleogonini), with a diagnosis and delimitation of the genus and description of five new species. Zootaxa 4298 (1): 1–77.

Zimmerman, E. C. 1992. Australian Weevils (Coleoptera: Curculionoidea) vol. 6. Colour plates 305–632. CSIRO Australia.

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