By Miller Zou
Originally published at ScientificAmerican.com
Marine and terrestrial ecosystems of the Indo-West Pacific are among the most biologically diverse regions in the world. Unfortunately, these areas are often ill prepared to combat non-native intruders, which, in many cases, can easily prey upon and out-compete their neighbors. These so-called ‘alien’ and ‘introduced’ species can quickly become invasive if environmental conditions are favorable (e.g., predators absent, nutrients abundant, etc.). Accordingly, the prevention and management of invasive species is a top priority for many geographically isolated ecosystems, including the Island of Guam.
Guam has a less than pleasant history with introduced organisms. During World War II the brown tree snake (Boiga irregularis) was unintentionally introduced while aboard a U.S. cargo ship, and have since caused the extinction of 10 of the 13 native bird species. Around the same time, Cane toads (Bufo marinus) were introduced to control sugarcane pests. Regrettably, the toads didn’t have their desired effect, as they spread to other areas and poisoned native predators with the toxin covering their skin (Fritts and Rodda 1998). Several frog species from Central America also have been detected that could pose a threat to crops. Guam’s biodiversity has been under siege for quite some time.
Currently, one of the biggest threats facing Guam’s native ecosystems is the invasion of the coconut rhinoceros beetle (Oryctes rhinoceros). Discovered in the Tumon Bay area in September of 2007, these organisms are notorious for their ability to decimate coconut palms. Adult beetles chew down into the folded, emerging fronds of coconut palm trees to feed on sap (Ridgell 2011). This boring behavior can be fatal to the tree if the meristematic tissue (i.e., where growth takes place) is jeopardized.
In other cases, the tree is left susceptible to secondary infection by pathogens (Hochberg 1991). Coconut rhinoceros beetles favor downed trees as breeding sites, so the mortality of young trees may be the first stage of a developing positive feedback cycle that would be essentially impossible to contain once initiated. To prevent this from happening young trees must be protected and dead ones must be cleared in areas of infestation.
The threat posed by these invasive beetles cannot be overstated. Guam’s native ecosystems lack the various biological factors (e.g., predation, disease) that control coconut rhinoceros beetle populations in their native range. With an abundance of palm trees and nothing to slow their growth, beetle populations are sure to explode if left unchecked.
If this invasive species is not controlled, massive mortalities of both cultivated and wild palms is expected. The coconut rhinoceros beetle has invaded other Micronesian islands before, with devastating results. Palau fell victim to the species in 1942 and on some islands coconut palms were completely eradicated, with overall mortality reaching 50% (Berringer 2007). Although managed by a few introduced infectious pathogens, in some areas the rhinoceros beetle has become permanently established and moved on to banana and sugarcane crops in areas cleared of coconut palms (Hochberg 1991).
Since the presence of O. rhinoceros was discovered in 2007, many methods of eradication and control have been implemented. The primary eradication program is a cooperative effort between the USDA, Guam Department of Agriculture, and the University of Guam.
The integrated eradication program uses pheromone-baited traps to capture adults, various methods to destroy infested and potential host material, and pesticides that can be applied to larvae, adults, or even uninfested trees as a preventative measure (Berringer 2007). Biological control has also been applied, using both green muscardine fungus (Metarhizium majus) and a baculovirus. While the beetles on Guam appear resistant to the baculovirus, the muscardine fungus showed a lot of promise when released in late 2011.
As of April 2011 the beetles are still spreading (Ridgell 2011), but newer methods give reason for hope. In addition to the green muscardine fungus, development is underway for the application of coconut beetle-detecting dogs and audio equipment that can quickly detect the presence of the species within trees (Mankin 2009). Guam’s battle against the foreign coconut rhino beetle is far from over, but at least now it has an arsenal of management tools to use.
About the author: Miller Zou is a junior working towards a bachelor’s degree in environmental studies at USC Dana and David Dornsife College of Letters, Arts, and Sciences. He is enrolling in a progressive master’s degree program in environmental studies and plans to take the scientific knowledge he has gained to law school to study environmental law and policy.
Berringer, Dallas. (2007) Coconut Rhinoceros Beetle Eradication Program: Guam. USDA Environmental Assessment.
Fritts, Thomas H. and Rodda, Gordon H. (1998) The Role of Introduced Species in the Degradation of Island Ecosystems: A Case History of Guam. Annual Review of Ecology and Systematics 29:1.
Hochberg, M.E. et al. (1991) A Model for the Biological Control of Oryctes Rhinoceros by Means of Pathogens. Journal of Applied Ecology 28:2.
Mankin, R.W. et al. (2009) Acoustic Characteristics of Dynastid Beetle Stridulations. The Florida Entomologist 92:1
Ridgell, Clynt (2011) Guam Losing Battle Against Coconut Rhino Beetle. Pacific News Center: Guam. April 6, 2011.
Editor’s note: Scientific Research Diving at USC Dornsife is offered as part of an experiential summer program offered to undergraduate students of the USC Dana and David Dornsife College of Letters, Arts and Sciences. This course takes place on location at the USC Wrigley Marine Science Center on Catalina Island and throughout Micronesia. Students investigate important environmental issues such as ecologically sustainable development, fisheries management, protected-area planning and assessment, and human health issues. During the course of the program, the student team will dive and collect data to support conservation and management strategies to protect the fragile coral reefs of Guam and Palau in Micronesia.
Instructors for the course include Jim Haw, Director of the Environmental Studies Program in USC Dornsife, Assistant Professor of Environmental Studies David Ginsburg,, SCUBA instructor and volunteer in the USC Scientific Diving Program Tom Carr and USC Dive Safety Officer Gerry Smith of the USC Wrigley Institute for Environmental Studies.