From discovery to eradication: the coconut rhinoceros beetle on Guam
March 30, 2012 12 Comments
It takes a large combined effort to successfully eradicate a plant pest. The Guam Coconut Rhinoceros Beetle Eradication Project has finally found a technique that could bring them their own eradication success story. The coconut rhinoceros beetle (Oryctes rhinoceros) was first discovered in Guam on 11th September 2007. Over the past five years it has caused severe damage to coconut palms, although its initial spread was slowed by the quick reactions of the government. It is now present in many parts of the island and, as coconuts are an important economic commodity for the US territory, is high priority for removal.
The beetles, which are native to south and southeast Asia, have devastating effects on palm trees at each stage of their life cycle. The adults bore into the trees to breed; as they bore through the growing points of the trees, new leaves can’t be produced so the trees die. This provides plenty of dead palms for the beetle larvae to feed on, allowing the life cycle to continue.
Many different techniques have been tried out in an attempt to rid the island of these beetles but, until last year, were largely unsuccessful in making a negative impact on the rhinoceros beetle population. Quarantine restrictions have been enforced, legislating that inspection and/or treatment of green waste and plants is required before it can be transported from an infested to an uninfested part of the island. Most of the control efforts have focussed on actively killing the beetles in various ways. More than 1700 bucket traps were hung up in palm trees, containing pheromones to attract the beetles and designed so they couldn’t escape. These traps didn’t result in sufficient numbers being caught to control the population but did give an opportunity to monitor spread. Sanitation procedures have involved removing all beetles and grubs from their breeding sites and destroying all infested live and dead plant material. Use of pesticides such as methoprene and cypermethrin was also implemented but with little effect.
There have also been some more novel ideas to control the beetles. The Coconut Beetle Eradication Team set up a hotline (475-PEST) for members of the public to report incidences of the beetles, rewarding them with T-shirts as an incentive. The first biocontrol attempt was in 2008, when a USDA-APHIS grant was provided to release a virus, which occurs naturally in Malaysia, that would kill the beetles. This has been successful on other Pacific Islands that have suffered from invasions of the rhino beetle but, on Guam, the virus had little or no effect on the beetles. As control efforts weren’t working and the beetles continued to spread, in 2009 four detector dogs were brought in to sniff out the beetle breeding sites. An expert in audio detection of insects from the USDA also made audio recordings of beetle communication sounds to develop a method of detecting the invasive species using acoustic monitoring devices.
By last year, none of the measures taken had led to eradication of the rhino beetle. This was when a biocontrol technique developed by the Philippines Coconut Authority was employed. Spores of Metarhizium, also known as green muscardine fungus, were imported at the end of 2011. This fungus was chosen because it only affects the rhino beetles. Following lab tests, powder containing the spores was distributed to farmers to apply to infested palms. A process of autodissemination has also been implemented – dusting trapped male beetles, which are then released so that they spread the fungal spores to undiscovered breeding sites. This has already been shown to be taking effect: sites that have been treated and revisited have been found with dead or dying beetles, and grubs found at previously unknown and untreated sites have been found dead as a result of infection with the fungus. This gives a good indication that the autodissemination method is working.
The coconut rhinoceros beetle population of Guam is now on the decline. According to the Eradication Program operations chief, Roland Quitugua, damage to coconut trees that can be seen now occurred about six months ago, before the fungus was introduced, and residents of Guam should soon notice a reduction in the number of newly damaged trees. It has taken much investment of time and resources, plus a fair amount of trial and error, but the continued combined efforts of the authorities should mean that, in Guam, the coconut rhinoceros beetle’s days are numbered.