![]() Downed trees and vegetative waste make ideal breeding sites for the beetle. ![]() The passing of Typhoon Dolphin over Guam in 2015 highlighted the dangers of an event like this triggering rapid growth in CRB populations. ![]() Smaller islands, where traditional, palm-dependent economies still operate, stand to suffer the most.įigure 1: “ The CRB-Guam biotype has invaded five Pacific Island countries and territories in only eight years compared to the CRB-Pacific biotype, which has not had geographical range expansion for 40 years“ There is now a real threat of a Pacific-wide outbreak of CRB. As well as Guam, the new biotype has now been logged in Papua New Guinea (2009), Palau (2014), Hawaii (2014) and the Solomon Islands (2015) (see figure 1). This resistance has proved paramount to the invasive ability of CRB. The Guam population was deemed a new biotype (CRB-Guam) and was found to be resistant to all available OrNV strains. Upon DNA analysis, the invading rhino beetles were found to be genetically distinct from CRB native to other Pacific regions. Early attempts at disseminating the virus in the new Guam population proved surprisingly ineffective. Up until Guam, 2007, it had been 40 years since an outbreak of CRB on an uninfested palm growing Pacific island, owing to the persistence of OrNV in beetle populations. As a biological control strategy, it has been highly effective at keeping CRB populations low and thus lessening palm damage by up to 90% ( Bedford, 2013). The principal method of rhinoceros beetle control is through the release of a virus specific to CRB known as Oryctes rhinoceros nudivirus (OrNV). The authors discussed the absence of international cycad experts from the contemporary conservation projects as a component of why the damage from the beetle was able to become established throughout the island without notice, and the continued absence of international experts from ongoing funded conservation projects will increase the probability of local extinction of the only native gymnosperm species in the region.A coconut palm damaged by CRB © Aubrey Moore The unexpected addition of the coconut rhinoceros beetle to the list of cycad herbivores reveals the need for continued observation of the cycad population by species experts so conservationists can best understand which of the threats are most in need of mitigation. "The damaged species included two families and four genera, so the dietary needs of the coconut rhinoceros beetle appear to be met at the cycad Order level," Deloso said. The beetle's burrowing activity in managed gardens at the University of Guam also includes highly diverse cycad species that originate from Asia, Australia, Central America, and the Caribbean regions. "When the CRB damage in our managed gardens began showing up on several cycad species, we knew that it was only a matter of time before the CRB host shifts included Guam's native cycad," said Benjamin Deloso, who curates the University of Guam's interpretive cycad garden. The WPTRC cycad team's sustained research has revealed that the severity of damage by each herbivore species has exhibited an undulating pattern, with the most severe damage at any point in time changing from species to species. Prior to the beetle's host shift, the cycad population on Guam was already suffering from chronic damage by numerous non-native insect and mammal herbivores, resulting in 96% mortality of the cycad population in the past 15 years. This kind of host shift is opportunistic and may occur without any co-evolution processes. "The CRB behaviors that we documented fit the 'ecological fitting theory,' which states that shifting to a new host species is due to compatible resources or signals in the new host," said Terry, who has been studying the relationships among insect herbivores and the native cycad plant since 2005. ![]() The authors used direct measurements of starch concentrations of the plant tissues to show that the island's heavily damaged coconut palms have declined in starch content so greatly that the host shift may have occurred in order to exploit the large doses of starch that are available in the cycad stems. "Where else have the most abundant and second most abundant forest species been threatened by the recent invasion of one non-native herbivore?" "Our initial alarm after documenting the CRB burrowing activity on cycad trees was the fact that Guam's cycad species was actually the most abundant tree on the island only 20 years ago," said Irene Terry, one of the authors of the study. The sustained efforts to develop an effective biological control program have not been effective, allowing the pest to establish a foothold throughout the island. The fact that coconut palms were the second most abundant tree on the island prior to the beetle's invasion was one factor that enabled the beetle's explosive population growth. ![]()
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