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  • By Johanna Salinas

More invasive species are coming into Guam and scientists can't keep up

On Oct. 23, 2017, Jake Manuel, a student of general entomology at the University of Guam, discovered a new butterfly species while collecting insects as a requirement for the course. The specimen, which Manuel found on a soursop leaf, had been identified as Doleschallia tongana.

“It was a new invasive species. I helped him get it identified,” said Dr. Aubrey Moore, a professor of entomology at UOG. “We contacted butterfly experts confirmed it.”

Also known as “Pacific orange leafwing butterfly,” the new species has the potential to do economic damage because it has been reported to feed on breadfruit. So far, it has not developed into a major pest on Guam.

As the region’s shipping and transport hub, Guam is a welcoming place for all planes and ships that come by. However, these crafts carry more than travelers and cargo. Invasive species find their way into Guam-bound carriers almost on a daily basis.

“Every day, we have new species coming in, but especially when they’re in cargo and produce coming from Asia or Christmas trees coming from Oregon,” said Dr. Ross Miller, a professor of Entomology at UOG, who works with Moore at the College of Natural and Applied Science.

“There’s always material coming in and a big problem that we have is that the rate of introductions has gone way up,” Miller said.

Each month, at least one or two new species are introduced to Guam. “Years and years ago, it used to be one or two every 10,000 years. Things happen very fast now,” Miller said.


He said UOG has been working with Dr. Russ Campbell, an entomologist with the Guam Department of Agriculture, to train Customs officials in recognizing invasive species and agricultural pests and to develop mitigation procedures to control their entry.

The most destructive invasive species on Guam are the brown tree snake, which is killing Guam’s native birds; and the coconut rhinoceros beetle which attacks palm trees.

Moore specializes in Guam’s rhino beetle problem and has hired entomologist Jim Grasela to help address the pest infestation on island.

“There are so many new insects I find when we’re out collecting on Guam. We have a lot of common insects but there’s still a lot I haven’t seen before,” said Moore.

Identifying every insect— even the ones native to Guam — can be challenging given their abundance. “When a new pest comes in with nothing to control it — no predators or parasites— and lots of food for them, it’s like paradise. We try to get it identified and look in the literature to see what controls it back home,” Moore said.

Miller said the new environment sometimes makes it difficult for pests to survive. “Most things that come into the island will die out on their own,” he said. “There are relatively new introductions that actually escape and become a problem,” he said.


Miller said almost every shipment of produce from off-shore comes with a certain insect. Many of them are species that are already present on Guam. “We don't worry about them too much,” he said.

What worries Customs inspectors and entomologists are the new species that could become pests.

Research and programs related to invasive species on Guam are funded by federal grants. “Science is expensive, but we get the money,” Miller said.

Last year, the Department of the Interior awarded the University of Guam a grant of $239,994 to establish biological control of the rhinoceros beetle population on Guam using two recently tested Nudivirus (OrNV) isolates (V23B and UOGT) that have proven to be effective in killing the CRB. The UOG grant formed part of the $942,200 awarded by DOI to Guam, CNMI, Palau and Yap through the 2020 Coral Reef and Natural Resources Initiative to eradicate and control the spread of invasive species that are disruptive to ecological systems and impacting communities and livelihoods in the islands.

But while grants may be available, Moore said the amount leaves much to be desired.

Over the last two years, Hawaii has received nearly $6 million to work on rhino beetle programs. Miller and Moore said Guam has had longer and more severe problems with the rhino beetle, yet it has received only $140,000.

The scientists also mentioned that in Hawaii, the rhino beetle isn’t killing trees but Guam is losing trees. “We still haven’t found a virus that is a catalyst for a biocontrol agent against the rhino beetles,” Moore said.

Moore and Grasela tried infecting the bugs with a virus that only kills rhino beetles. However, Guam’s rhino beetles are immune.

“We were hoping we’d have this stuff out in the field by now,” Moore said. “It’s not just Guam that’s impacted by this particular pest. It's islands in the South Pacific.”

The new strain called “CRB-Guam” is a growing threat to many Pacific islands, where the infestation is estimated to cost the region $169 million a year by 2040 if the pest invasion is not curbed.

“The Coconut Rhinoceros Beetle-Guam has ‘Guam’ in its name because it was discovered here. We introduced the rhino beetle virus but it didn’t do anything,” Moore said. “A scientist from New Zealand told us Guam’s beetle is different and that it’s connected to the resistance to the virus. We’re still not too sure.”


The little fire ant is another great pest infesting the islands. It is tiny — like a dot on a page — yet, it is considered one of the top 10 worst invasive species in the world. Fire ants can sting, causing red, swollen spots that blister, itch and hurt.

“What they do is go into an area, then gradually spread and kick out the other organisms that are there,” Miller said.

There are more than 60 ant species on Guam. Ten are native, the rest are what Miller calls “tramp ants.”

“They come here and get established and become pests,” he said. “If you see ants outside, most likely they’re from Central and South America or even Africa. They’ve been here for probably 100 years. The little fire ant just came a few years ago.”

If scientists are unable to identify a pest, they either use photography or send the pest through courier mail to another lab.

“Part of my job is being an identifier,” Miller said. “We help USDA and GovGuam and make recommendations on what they should do about whether shipment should be allowed or be cleansed or destroyed or sent back, and then they decide what they would do. It has to be done quickly because if a shipment is out in the harbor, they’re losing money every hour it can’t be unloaded.”

While it may seem logical for the pest's native country to assist “It’s usually the responsibility of the receiving country to keep things out or deal with it when it comes,” said Miller. “It only takes one insect to cause an outbreak—you don’t even need two. The economic cost of the environment is astronomical.”

Miller, for example, recalled the disaster caused by the arrival of the Asian cycad scale on Guam.

The Asian cycad scale was discovered on ornamental cycads on Guam in 2003 and spread to the native cycad. Without treatment, the mortality rate for native cycads was 100 percent within one year of infestation “We now lost cycad trees—it's on the endangered species list,” Miller said.

Though it is the duty of the receiving country to deal with pests, Miller said Guam must try its best to protect the rest of Micronesia from invasive species.


“The tropical fire ant is a pest on all of our islands in Micronesia. Because Guam is a hub for shipping and air transport, we get a lot of invasive species. Our big challenge is protecting the other islands from getting those.”

The Covid 19 pandemic has made it difficult to also collaborate with scientists throughout the region. “Research takes longer now and travel is impossible.

We're not able to do some projects because we can't get off islands without doing a quarantine,” Miller said. “We can't go to the mainland to pick up biocontrol agents to bring back. Now, we planned so that projects avoid traveling.”

Miller’s projects were primarily for Guam, Saipan, Tinian and Rota, in collaboration with institutions in Hawaii and the U.S. mainland.

Besides tackling invasive species, Moore’s biggest goal at UOG is to train students to become scientists. “One thing we need to do on Guam is grow our own expertise. That's what UOG is supposed to do. We need to train entomologist to take our place,” he said.

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