Chemical treatment of coconuts, Orytes, Samoa Minimize

January 2016. A question on what insecticide to use on Oryctes rhinoceros on young or short palms.

On Guam, young/short palms are treated with biweekly foliar application of cypermethrin.

A member gave some other information on the infestation and that is recorded here:

The virus and the rhinoceros beetle show what is called a typical density-dependent relationship. In low populations, there is little contact between beetles and therefore little chance for the spread of the virus. As the population of beetles increases, so does the virus, but this is generally slightly behind the increase of the beetle. When the population becomes large and there is more chance for beetles meeting, then the virus can spread rapidly, causing the beetle population to crash.

This is why during the Rhino Beetle Project, we still emphasized that getting rid of rotting logs and sawdust was important. Colin Little even developed a special kiln for making charcoal from coconut wood so that the wood could be removed. One was built at Faleata. Metarrhizium may have value in piles of sawdust.

It seems to me inevitable that should there be a sudden increase in the number of dead coconuts - after a cyclone, tsumani or drought - then sometime later there will be a proportionate increase in beetles.

As to the treatment of palm crowns this is very difficult - in 1950-1980, Fiji used to treat regularly the crowns of the street coconut trees in Suva with BHC. This was marginally effective - and nowadays we recognise the downsides of using organochlorine chemicals leading to pesticide residues and build-up of such chemicals in waterways and the lagoon, where they can kill fish. Milt Stelzner also looked at stem injection of chemicals for rhino beetle control - one danger was the possible build-up of such chemicals in the coconuts themselves.

The Rhino Beetle Project came to the conclusion that the best way to augment the effect of the virus was to remove as much of the breeding sites of the beetles - obviously this is a huge task after cyclone damage.