October 2010. The identity of a weevil causing secondary damage in oil palm trunks in Northern (Oro) Province, Papua New Guinea, was requested.
In India, secondary infestation of Red palm weevil (Rhynchophorus ?palmarum) occurs in oil palm that are infected by bud rot disease. Xishuangbanna Tropical Botanical Garden in South China has had significant problems from this pest on a range of palms. However, it was not thought to be this by the sender in PNG. Neither was it the African oil palm pollinator, Elaeidobious kamerunicusFaust (Coleoptera: Curculionidae), which is only about 3 mm; this insect is 20 mm.
It’s a genus of Dryophthorinae: Rhynchophorini: Sphenophorina close to Rhabdoscelus, but differs from all species of this genus in the Australian collection by having a shorter, broader scutellum. No other genus of Sphenophorina in the collections fits.
Red palm weevil (Rhynchophorus ferrugineus) was recorded from (intercepted in) Australia at least four times, but appears not to have established in Australia. It seems to be common in New Guinea though, so might be just a matter of time before it gets there.
There then followed a long exchange of emails on the records of R. ferrugineus from PNG. Is it present, and, if so, where was it recorded. PNG Oil Palm Research Association Inc., Dami Research Station, has not yet recorded it from oil palm. Australia (CSIRO) has a collection of Rhynchophorusfrom New Guinea, which all appear to be the same as those recorded as R. ferrugineusfrom Australia. However, there is need to check they are that species and not R. bilineatus, which seems to be the southern species in the Pacific region. But Wattanapongsiri also recorded R. ferrugineusfrom New Guinea (Port Moresby) in his 1966 revision of the genus. The external differences he gives between these two species are not clear-cut, and it’s possible that several specimens of R. ferrugineusin the Australian collection have been misidentified according to W’s differences. At the moment it is not possible to say what exactly Australia has that is from New Guinea (or from Australia, for that matter).
Lincoln University also made suggestions: It’s a member of the Dryophthorinae, and looks to be in the tribe Sphenophorini, possibly Sphenophorus.
A checklist of the weevils of PNG was published in 2007, which may be useful for narrowing the possibilities.
Another suggestion came from the NHM; as the insect is approximately 20 mm long, it matches Sparganobasis sp. (Curculionoidea: Dryophthoridae: Rhynchophorinae: Sphenophorini). There is only one species currently described, S. subcruciatus Marshall (the coconut bole weevil; distribution New Guinea – Solomons Islands). This seemed likely to be the identification.
References to Sparganobasis subcruciata are to be found in the following journals:
Arrow G J, Marshall G A K, Gahan C J, Blair KG (1915) Report on the Coleoptera collected by the British Ornithologists’ Union Expedition and the Wollaston Expedition in Dutch New Guinea. Transactions of the Zoological Society of London 20(16): 497-542).
Frogatt JL (1936) Coconut pests: pests of the trunk. New Guinea Agriculture Gazette 2(3): 18-21)
[Note: A machine that reads the DNA of the red palm weevil (but what species?) is said to have been invented as a means of detecting it in the trunks of oil palm. Successful detection will lead to lower rates of insecticide used. An article appeared online in SciDevNet 11 May 2011: http://www.scidev.net/en/news/weevil-detector-could-protect-palm-trees.html.
In another paper in PLOS one, Lohr et al. (2015) Rhyncophorus palmarum in disguise: undescribed polymorphism in the “black” weevil, the authors found five beetles in a pheromone mass trapping exercise that were typical of coloration of R. ferrugineus. But conventional taxonomy and molecular analysis put them in the R. palmarum group. (http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0143210).
And according a member who agreed that is morphological similarity between the two species and that some red palm weevils are totally black.