Life cycle questions, Oryctes, Palau Minimize

November 2011. Coconut trees on the small and remote island of Fanna, Palau have been devastated by the coconut rhinoceros beetle: only a few trees remain.  Fanna is located over 200 miles southwest of the main Palau archipelago, and is part of Sonsorol State.  The Lieutenant Governor of Sonsorol has asked for advice. Here are the questions:

  • If there are no more coconut trees on Fanna, will the beetles eventually die out, or do they have an alternate food source?  If no alternate food source, then the few remaining coconut trees could be cut down, and the immature beetles would complete their life cycle and starve.  
  • If there are alternate food sources for the beetles, what are they?
  • How long will it take the immature beetles to complete their life cycle and die out?
  • Can the beetles re-infest Fanna by flying one mile from Sonsorol Island?

Answers came from members as follows:

It was thought that the beetles ate Pandanus after killing all of the coconut trees on some of the smaller islands in Palau during the original invasion (reported in Gressitt's monograph). Adults will attack banana and sugarcane for sap, and larvae do well on a range of substrates with high organic content. Normal generation time in the lab is 9 months to 1 year, but this may be extended if grubs are malnourished. It would be best to wait at least 2 years, before replanting. The literature reports flights of a few hundred meters for rhino beetles, but possibly a beetle could fly a mile or more in a no-choice situation, such as being pushed out to sea by a strong wind.

Another menber told of tests made on the time that a beetle was indued to fly. A carousel was made and a male beetle attached which flew round and round at 5 mph for 40 minutes, after which it folded its elytra and refused to fly further. So that would give it a range of about 3.3 miles.