Pests > Pests Entities > Insects > Beetles > Weevils > Rhabdoscelus > Dead betel nut, Palau

Pests > Pests Entities > Insects > Beetles > Weevils > Rhabdoscelus > Dead betel nut, Palau

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Dead betel nut, Palau

September 2016. A homeowner reported that four betel nut (Areca catechu) trees, about 4-5 years old, were all dying at once. The trees are in a row, with less than 1 m between them, about 2 m tall. The leaves began turning brown in June, and now all four trees have died. When the dead leaves are pulled off, there were quite a few different insects inside, but it was not possible to tell of these came before or after death. There was no sign of external insect damage, such as boreholes. Two of the trees have rotted and bent over, while the two others are still hard and strong, but the shoot tips have died. There was no foul odour as has been reported from betel nut bud rot on Guam.

The farmer reported that the same thing happened with a few trees about the same age last year, but all other betel nut trees at her house – both mature trees and seedlings – appear healthy: this has only happened with trees that are just about to begin bearing.

One member asked about insect larvae in the stem as there were signs of frass. And, yes, some ooze was seen, but not holes. A possibility was the sugar cane weevil, Rhabdoscelus obscurus. It was not known why only those four were attacked, but it was said that any betel nut palms that were under stress seemed to be more susceptible to insect infestation.

Later, when the member reporting the problem in Palau went back to inspect the palms holes were found when the trees were split. Larvae were there, and there were many beetles. The head of the adults was orange-red and the thorax had black elytra. The largest larvae was almost 1.5 cm long; but the adults were only about 5 mm long, and likely to be unrelated.

And this was supported by other members. Rhabdoscelussp. [there are a number of species](note the spelling) weevils are commonly found in parts of palms which have been affected as a result of damage (wind, poor pruning, lightening, etc), and the best option is definitely to try to rear them through. (Remember not to kill the adults until they have properly hardened).

Adults should go to a specialist (for example, Drs Rolf Oberprieler-Australia or Chris Lyall-NHM, UK), but good photos will be needed, and preferably specimens in case dissection is required, or detailed taxonomy is required. It is always useful to know exactly what is causing the problem, even if it was secondary!

The grub is a weevil, probably involved in killing the betel nut palms, and the small adult beetle (a nitidulid, possibly) was probably attracted to the decaying crown.

For an identification of R. obscurus see:

  • F. A. BlANCHI. Observations on Rhabdoscelus obscurus (Boisduval) and Rhabdoscelus asperipennis (Fairmaire) in Micronesia, EXPERIMENT STATION, HSPA, HONOLULU, HAWAII.
  • R. P. Owen.trUST TERRITORY OF THE PACIFIC, KOROR, PALAU (Submitted for publication December, 1964). It mentions that R. obscurus is present in Palau.
  • Napompeth, B., T. Nishida, and W. Mitchell. 1972. Biology and rearing methods of the New Guinea sugarcane weevil, Rhabdoscelus obscurus. Technical Bulletin No.85. Hawaii Agricultural Experiment Station, University of Hawaii. 51pp.

    Find a diagram of the life cycle of the red palm here:

Finally, a question was asked by a Pestnet moderator: how about introducing the tachinid fly, Lixophaga sphenophori, from Hawaii (contact HDOA, Honolulu) or PNG (contact Dr. Kuniata at Ramu Sugarcane Research Center).