Coconut Rhinoceros Beetle or Oriental Flower Beetle? New Genetic Test Gives Faster Answer

Just more than three years ago, the coconut rhinoceros beetle (Oryctes rhinoceros) arrived in Hawaii, on the island of Oahu. The invasive species is native to Southeast Asia and has not yet become widespread on Oahu, and insect scientists there are working to keep it that way, as the beetle is a damaging pest of the coconut palm tree.

That’s not an easy job, and complicating matters is that another invasive beetle, the oriental flower beetle (Protaetia orientalis), is widespread in Hawaii, and the eggs, first-instar larvae, and droppings of the two species are morphologically indistinguishable. That means identifying the two has required raising larvae specimens to their third instar (life stage), which can take several weeks.

Scientists at the University of Hawaii, however, have developed a new method—leveraging an increasingly common form of DNA test—that promises to make that process much quicker, and thereby better enable the identification emerging populations of the coconut rhinoceros beetle. Their method is reported in a new article published in the Journal of Economic Entomology.

Researchers Shizu Watanabe, Ph.D. and Michael J. Melzer, Ph.D., of the Department of Plant and Environmental Protection Sciences, College of Tropical Agriculture and Human Resources, at UH, identified genetic markers in the beetles that can be used for differentiation via a multiplex polymerase chain reaction (PCR) assay, and the DNA material necessary for the test can be extracted from the beetles’ eggs, larvae, or excrement. Once samples are brought to a lab, the PCR assay can be conducted in just a few hours, Melzer says.

The new method will help “ensure that eradication efforts are being directed at coconut rhinoceros beetle and not oriental flower beetle. This assay will help to prevent any misidentification in the field,” Melzer says. “Such misidentifications might result in resources targeting oriental flower beetle, or worse, ignoring a coconut rhinoceros breeding site because the specimens discovered were identified as oriental flower beetle.”

The molecular assay method for identifying insects, when developed for specific species, can be an important resource in efforts to stay one step ahead of invasive species—such as this recent example of a portable immunoassay test for red imported fire ants.

“For species that require highly technical expertise for identification, molecular assays represent a reasonably straight-forward approach for identification, either as stand-alone assays or in parallel with morphological identification,” Watanabe and Melzer write in their article. “For pests of regulatory concern, rapid and accurate insect identification is essential, and molecular assays can address these needs.”