The Guam Department of Agriculture has taken a major step onto the international scientific stage with new research confirming what beekeepers here have long warned. The invasive Vespa tropica, or the greater banded hornet, is firmly established on island and taking a toll on honey bee colonies.

The study, titled “Predatory behavior, nesting habits, and impacts on honey bees (Apis mellifera) of an invasive hornet (Vespa tropica) on the island of Guam,” was published this week in the peer-reviewed journal PLOS ONE. It represents nearly a decade of monitoring hornet activity across Guam.

Drawing from beekeeper logs, public reports, nest collections, and video recordings, researchers documented how the greater banded hornet hunts and harasses hives throughout the year. In peak years, up to 12 percent of managed honey bee colonies have been wiped out.

“We are excited that one of our very own DOAG State Entomologist led this work in cooperation with national and international scientists,” said Chelsa Muna, Director, Guam Department of Agriculture. ?“By contributing to peer-reviewed science, we are elevating Guam’s voice in understanding invasive species impacts in island ecosystems.”

Biosecurity Division Chief Christopher Rosario, the study’s lead local author, added that public participation has been critical.

“The relationships we’ve built between DOAG, beekeepers, and the public have been crucial. Without public reporting, many nests may have remained undiscovered,” Rosario said.

The findings likely come as no surprise to local beekeepers, who have been sounding the alarm for years. KUAM has reported on colonies being decimated by hornet attacks. Beekeepers have said they have to swat away hornets multiple times a day at their apiaries, a temporary solution unless nests are destroyed.

The threat isn’t limited to bees. Rosario has warned on KUAM that the hornets’ venom packs a punch, can sting repeatedly, and pierce through protective bee suits. In response, DOAG and its partners have begun testing tracking methods, including tiny radio transmitters attached to hornets to help locate nests before they spread further to sister islands.

In their next steps, DOAG plans to pinpoint the geographic location where these invasive hornets came from. Early analysis suggests they most closely resemble populations in Southeast Asia, though genetic testing is still underway.

DOAG says the publication highlights the need for stronger border control to prevent additional invasive species, while giving beekeepers data-driven guidance on hive defense strategies.

The department is urging the public to continue reporting hornet sightings through its Pest Hotline, especially during the wet season from July through December when hornet activity spikes.

The study is openly available to researchers worldwide, underscoring Guam’s role in contributing knowledge about invasive species on small islands, knowledge that could shape biosecurity strategies far beyond the region.