Pests > Pests Entities > Insects > Beetles > Weevils > Rhabdoscelus > Sugarcane weevil, Rhabdoscelus obscurus, CMNI

Pests > Pests Entities > Insects > Beetles > Weevils > Rhabdoscelus > Sugarcane weevil, Rhabdoscelus obscurus, CMNI

Pests Pests Entities Insects BeetlesWeevilsRhabdoscelus Sugarcane weevil, Rhabdoscelus obscurus, CMNI

Sugarcane weevil borer

March 2000. The weevils were taken from the upper stem of beetle nut, below the crown. As mentioned previously, they are not new to the CNMI, but the populations appear to be increasing.

CNMI has been experiencing a lethal yellowing and crown dieback of betel nut for the past several years. Isolations from symptomatic plants have resulted in a Pseudomonas and a possible mycoplasma (phytoplasma) presence. We have sent specimens to USDA-Beltsville for positive identification of the pathogens. We are treating it as a disease complex and have suspected several insect carriers, but have not proven transmittal or transference of pathogens at this time.

The identification of the weevils was requested as well as management strategies.

Members said that the smaller ones could certainly be a species of Diocalandra, but whether it was D tahitensis or D frumenti, was not known. Clearer pictures of the colour patterning on the Diocalandra and the Rabdoscelus are needed.

The Queensland Horticulture Institute, Centre for Tropical Agriculture, had a research project on Sugar cane weevil borer in palms about 6 or 7-years’ ago. The weevil had started to create problems for the palm nursery industry in north Queensland, following an increase in green cane harvesting in the sugar industry and some use of sugar cane bagasse in potting mixes and as mulch. A wide range of palms are known to be hosts of Sugar cane weevil borer, including the betel nut. Some good background information on this problem can be found in:

Halfpapp KH, Storey RI (1991) Cane weevil borer, Rhabdoscelus obscurus (Coleoptera:Curculionidae), a pest of palms in northern Queensland, Australia. Principes Vol. 35: 199-207.

The tachinid parasite of R obscurus, Lixaphaga sphenophori, was introduced from PNG to Australia early last century, but does not exert sufficient control on weevil borer in palms in the majority of situations. Therefore chemical and cultural treatments were developed against weevil borer for the nursery industry. These included:

1) application to run-off of chlorpyrifos (5 -10ml/l of 500 g/l EC) to the leaf bases, trunk and basal soil – 2 applications one month apart during major periods of weevil activity;

2) removal of old and dead fronds which shelter adult weevils;

3) destruction of heavily infested plants; and

4) cessation in the use of bagasse in potting mixes and as mulch.

Both prothiophos and bifenthrin were almost as efficacious as chlorpyrifos, and subsequently fipronil has been shown to have good activty against weevil borer too and is used in the sugar industry.

Also, there have been some relatively recent studies on the pheromones of palm weevils (including Rhabdoscelus) by Robin Giblin-Davis (University of Florida, Fort Lauderdale). An online publication can be accessed at:

Giblin-Davis RM et al. (1996) Chemical and behavioral ecology of palm weevils (Curculionidae:Rhynchophorinae). Florida Entomologist Vol. 79:153-167.

An aggregation pheromone is reported. See Pests>Pest Management>Chemical control> Pheromones.