A temporary ban on mangoes from the Commonwealth of the Northern  Mariana Islands to Guam is in effect after researchers found an invasive insect chewing up the fruit in Saipan. Called the Mango Fruit Borer, this pest feeds on the mango’s pulp and seed, damaging the crop.  Experts cautiously suspect the pest may have already made its way to Guam, which could have a “devastating” impact on the beloved fruit. 

During a routine site visit to Saipan about two months ago, several researchers from the University of Guam made an unexpected discovery. "On one of the mango trees, there was this larva, this worm, chewing up the inside of the mangoes," explained Guam Department of Agriculture’s biosecurity chief and state entomologist Christopher Rosario. He added that a DNA analysis was sent to a lab off-island.

"It was then later identified as mango fruit borer. And mango fruit borer is a major pest of mangoes," he confirmed.

Following the discovery, the agency is temporarily banning the importation of mangoes from the CNMI to Guam until further notice. They say the strict measure is required to prevent the spread of what’s known to be a significant pest. 

Rosario says the Mango Fruit Borer is a moth that originates from Southeast Asia and the Northern Territory of Australia. It lays its eggs on the mango and when they hatch, the larvae bore into the fruit, damaging the crop. 

Rosario continued, "It’s very difficult to tell whether a mango is infested with mango fruit borer, because there is another mango pest that we do have. It’s called mango seed weevil, which generally they’ll bore into the seed. This bores into the fruit, so it eats the fruit itself."

Although a ban is in effect, Rosario says uog’s entomoglist DR. Daniel JOHNSON cautiously suspects this invasive pest may have already made its way to Guam. They’ve tested a sample found locally and are currently waiting for the lab results. 

"It’s still kind of in the works. We’re still trying to figure out if mango fruit borer has made its way to Guam," said Rosario. "I don’t want to start ringing the alarms yet until we get full confirmation. But Dr. Johnson suspects we may also have it already."

Mangoes hold a cultural and culinary significance for the island, so much so that the village of Hagat even has an annual festival dedicated to the abundant crop. "Mangoes are a huge way of our life. As far as its impacts, we know there is a lot of mango, so there’s a lot of potential growth for this mango fruit borer to also invade. So for me, I say the impact could be devastating," he added.

A potential devastating impact that’s a reality for another favorite backyard fruit hit hard by an invasive pest.  As KUAM News reported last July, the invasive hog plum beetles were discovered sweeping across the island defoliating spanish plum trees, locally known as siniguelas. 

Now over a year later, the hog plum beetles have grown out of hand. "It's really hard to see the impact only until about several years later. The hog plum beetle is an example where not a lot of people grow siniguelas in their back yards, but those who do, do see the impacts on their trees," said Rosario.

It’s why he says better integrated pest management for the mango fruit borer will be key, noting, "And this is why the research is very important, to look at what are potential biocontrol agents for this pest. What are safe pesticides or insecticides that we can use? And what other cultural methods can help us better manage this mango fruit borer if it is on Guam."

For the time being, DOAG says the ban is a temporary measure to ensure the safety of Guam’s mango industry and to allow time for the department to sufficiently inform, advise and train Customs and Quarantine inspectors at the borders to inspect and identify mangoes that may carry this pest. 

If you see any larvae munching on your mangoes, you are asked to call the Guam Pest Hotline at (671) 475-PEST (7378).