Varroa Eradicated from Guam

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Photo 1 The honey bee colonies in the initial APHIS survey, line pointing at the initial detection, with second detection near it.

Photo 2 GU-12, the

first detection

I made a shocking discovery the other day … which was that Christopher Rosario made a shocking discovery a few years ago. I was browsing through a recent issue of Entomology Today, as one does, and there was an article1 that mentioned that Guam State Entomologist Christopher Rosario had “eradicated an invasive parasite,” but didn’t mention which one. Eradicating an invasive parasite is always a worthwhile activity so I thought I’d contact him to find out what he had eradicated.

“Varroa mites,” he wrote back.2 I about fell out of my chair. I recovered myself, repeating surely, surely it was just the less dangerous “Varroa jacobsonii” though. So I asked him. “Varroa destructor,” he said. For the next few days, “Have I told you about Guam??” was all I could say to anyone.

Now before I tell you his story, let me tell you about Guam. Guam is a small island in the west Pacific about 1300 miles east of the Philippines, 1000 miles north of Papua New Guinea, and 1,500 miles south of Japan, which is to say really far from the nearest “mainland” of any kind. The island is 210 square miles in size, which, to compare to an island you might be more likely to be familiar with, is about a quarter (well 29%) of the size of the Hawaiian island of Maui, with just a slightly

higher population. The population of Guam is relatively concentrated in the north, with the population of the more rugged south mostly limited to coastal villages. The south has, according to Rosario, “mostly lots of rivers, ponds, and waterfalls,” and having Googled it myself, the waterfalls look very pretty.

Which brings us to our story. Christopher Rosario, a native of Guam, had graduated the University of Guam in 2012 with a bachelor’s degree in biology and wanted to become a veterinarian. In 2013 he found a job opening as a field technician conducting the Project APHIS (USDA Animal and Plant Health Inspection Service) National Honey Bee Survey (NHBS, https:// ushoneybeehealthsurvey.info/) to see if varroa or Tropilaelaps mites were present in Guam and the Northern Mariana Islands. Not having a background in beekeeping, he was initially afraid of getting stung to death, but he had a lot of debt from his bachelor’s degree, and veterinary school would only have added to it, so he applied for and got the bee survey job.

Also relevant to our story here, Guam is not entirely alone in the Pacific; the Commonwealth of the Northern Mariana Islands (CNMIs) is another cluster of islands of which the main islands are 50-125 miles north of Guam. Both Guam and the CNMIs are U.S. territories — I for one had no idea the CNMIs existed, nor that we have a type of territory that is itself a commonwealth, but there you go.

Honey bees are, of course, not native to Pacific Islands. Apis mellifera ligustica, the Italian bee, was first introduced to Guam in 1907 from Hawaii (where bees had arrived in 1857 from California,3 where bees had only arrived in 1853,4 but I digress), with some follow-up importations of more bees until in 1954 the Organic Act of Guam was signed, which banned further importation of honey bees to Guam. The Northern Mariana Islands continued to import bees from Hawaii until 2010 … varroa had arrived in Hawaii in 2007.5

The NHBS wanted him to survey 24 apiaries, but there was a problem — there were only four established apiaries on the island! He put word out in the local media requesting the public to call in feral colonies, and soon three to four times a week people were calling him to remove colonies from their homes, or asking how to start keeping bees.

On the 3rd of March 2014,6 near the village of Malesso beside the Cocos Lagoon, he was called out to a large exposed colony 25 feet up in a monkeypod tree (Samanea saman, Photo

2). Up he went in a cherrypicker lift to reach the colony, calmed the bees with a smoker, and swept up flying bees around the colony with an insect net until he had about a quarter cup of bees. The bees were then funneled into a bottle with ethanol, to be sent to the University of Maryland for analysis.6 Job done, down he went and on to the next site; he was just a technician after all, it was for the lab to analyze. Altogether he took samples on Guam from 18 feral colonies and two domestic ones.

Then he proceeded to the Northern Mariana islands of Saipan and Tinian, where they sampled four colonies and three of them immediately, obviously, were positive for varroa. “Mites were crawling out of the bottle!” Rosario says.

Back in Guam a month went by before he heard anything more about that exposed colony beside the lagoon. Then he got the bad news in a call from his boss, the then State Entomologist of Guam, Dr. Russell Campbell. That and one other feral colony also on the southern coast had both tested positive for low levels (1-2 in the sample) of mites.

“I had no idea how bad they were until I was told that the bee colony needed to be eradicated,” Rosario relates. “I was a student fresh out of college that did not know anything about honey bees [or their pests].”

Photo 3 Christopher Rosario with a swarm reported by a resident, April 2021

Photo 4 Rosario sees a real varroa mite up close for the first time, looking at the sample from Tinian Island back at University of Guam’s Bioquarantine Lab.

The territory’s entomologists were all understandably shocked. This hive would need to be put down immediately! Fortunately they had a Coconut Rhinoceros Beetle eradication team led by invasive species specialist Roland Quitugua, with a truck-based insecticide sprayer and 40-50 gallons of cypermethrin. “It was so saddening to watch,” Rosario says of watching them hose down the colony.

were eradicated. (“It was then that I learned to do euthanasia with soap and water.”) Since 2017, despite constant monitoring, no mites have been detected.

Rosario believes the mites had probably come from the Northern Mariana Islands, where varroa is pervasive. Despite the import of bee stock being illegal, it is believed someone had smuggled bees in from the CNMIs or Hawaii, either by boat or air cargo.

Two sentinel hives were then put near the area and monitored. Nothing else was found until the following year, when mites were detected in one of the sentinel hives — again from lab analysis, because a low-level mite infection is less likely to show in an alcohol wash (in until-recentlymite-free Australia, samples from sentinel hives are also sent for lab analysis,7 and that’s how mites were first detected in June 20228). Despite doing alcohol washes at the time of sample taking, “I have yet to witness a mite in a bee colony in Guam,” Rosario says, as all detections have been at such low levels they were only caught in the lab.

Also Rosario, the Guam Department of Agriculture, and the University of Guam have been promoting managed beekeeping, so that local beekeepers will spot and report any further exotic pest incursions. When Rosario began surveying in 2013 there were only three beekeepers in Guam. As a result of his public calls to report bees, he was hearing from all these people who either had bees or wanted to get into beekeeping. He noticed “a harmony between people wanting to get rid of bees on their property, and people wanting to keep bees on their property.”1 So he rehomed the unwanted bees to the people who wanted them.

Two colonies with varroa were detected in 2016, and one in 2017. All

Photo 5 Christopher Rosario and apiary inspectors from across the U.S. made their way to Thailand for a Tropilaelaps detection workshop conducted by Auburn and Chiang Mai universities, and funded by the North Dakota Dept. of Agriculture and Project Apis, in January 2024.

The small community of beekeepers grew by about 10 a year, jumping from 55 to 105 during COVID as interest in hobbies one can do at home peaked. Now there are 115 beekeepers in the Guam Beekeepers Association (https://www.guambeekeepers.org/) managing about 250 hives, including six beekeepers commercially selling their honey. Rosario estimates that for every managed hive, however, there are 10 feral hives (which would equal the 1.7 hives per square mile estimated for Oceania in a recent meta-analysis of feral colony densities9).

This push for people to call in about bees may have helped detect another invasive pest — in June 2016 someone called in a bee colony that turned out to be something much worse. By the shores of clear and shallow Tumon Bay in the northern built-up part of Guam, where the Hyatt and Hilton overlook the beach, Rosario was called to look inside a hollow old avocado tree. There he found not a bee colony but an ugly nest of several tiers of dark paper mâché cells filled with bright white pupal cocoons like an arsenal of missiles ready to launch,

(as Dr. Campbell put it2). Today the Guam Department of Agriculture, Customs and Quarantine Agency, and U.S. Department of Agriculture APHIS Plant Protection Quarantine, work together for management and prevention of invasive species. It is estimated that every year a hundred invasive species arrive in Guam via the ports, with three successfully establishing themselves.1 Coconut rhinoceros beetles (Oryctes rhinoceros), little fire ants (Wasmannia auropunctata), and Asian cycad scale (Aulacaspis yasumatsui, an insect which attacks Guam’s native Cycas micronesica, a ferny plant) are a few examples of other invasive pests that have unfortunately become established. The rhinoceros beetles have destroyed over half the island’s coconut trees.

and covering this and flying around it were large inch-long brown hornets with a single broad yellow band around their abdomen: the greater banded hornet, Vespa tropica. Soon they were being found all over the island; it was already too late to prevent them from taking hold.10

It’s believed the hornets came in an empty cargo container on a ship from Southeast Asia. Rosario, sensing what a threat this species was, was “extremely devastated” when he found the hornets. Other entomologists assured him they weren’t a pest of honey bees, but that sadly proved untrue. These hornets’ first preference for prey is paper wasps, and the island’s wasp population (Polistes olivaceus and Polistes stigma — these wasp species were themselves introduced via Japanese vessels in WWII2 — known locally as “boonie bees”) immediately crashed. Running out of wasps to eat, the hornets turned to bees, and 55 managed colonies have been lost to hornets to date (one out of every six hives!).

Chris Rosario, you will recall, had wanted to be a veterinarian when he found work as a technician in the honey bee survey. “This survey opened my eyes to research because so little was known about honey bees in Guam. It then made me want to go into graduate school, where I used this survey as my research project,” Rosario told Entomology Today.1 In 2021 he received his master’s degree in environmental science with a focus on entomology. His boss, Dr. Campbell, happened to be retiring, and Rosario successfully applied for the position, becoming the first native of Guam to be the island’s state entomologist.

Guam is so far free from foulbrood (European or American), or small hive beetle, though they do suffer from chalkbrood due to the high humidity.

Guam does not have any specific biosecurity officers. In 2003 the Plant Protection Quarantine officers they had had were merged into the Guam Customs and Quarantine, “which essentially gutted the Department of Agriculture’s biosecurity program”

Photo 6 Rosario uses a bee vac to relocate bees from where they’re unwanted to where they’re wanted.

A version of this story first appeared in the August 2024 Australasian Beekeeper.

References 1 Serrano, J (2024) “How One Entomologist Works to Combat Invasive Species and Protect Honey Bees on Guam.” Entomology Today https://entomologytoday. org/2024/03/25/entomologist-invasivespecies-honey-bees-guam-christopher-rosario-standout-early-career-professional/ 2 All otherwise uncited quotes and details: from personal communication with Christopher Rosario June and July 2024 3 Roddy, K., Arita-Tsutsumi, L., (1997) “A History of Honey Bees in the Hawaiian Islands.” Journal of Hawaiian and Pacific Agriculture Volume 8 No 1 https://hilo. hawaii.edu/panr/writing.php?id=198 4 Harbison, J.S. (1919) “Introduction of the Honeybee to California.” American Bee Journal (59)9: 268-270 5 Prendergast, K., (2017) “Mites Hawaii and the Varroa Mite: A case study.” https:// blythewoodbeecompany.com/blogs/ news/mite-in-hawaii-and-the-varroamite-a-case-study 6 Rosario, C., Moore, A., & Miller, R. (2014).

Varroa mite, Varroa destructor (Acari: Varroidae). Guam New Invasive Species Alert No. 2014-04 (2014). Retrieved from https://guaminsects.net/anr/sites/default/ files/varroa%20mite_0.pdf 7 Huntsdale, J., (2018) “Sentinel Beehives Provide Coastal Defence Against Catastrophic Varroa Mite Invasion” Australian Broadcasting Corporation Feb 23rd https://www.abc.net.au/news/2018-02- 23/sentinel-bee-hive-program-defendingagainst-varroa-mite/9470992 8 Hilton, A., (2024) “Varroa mites have infested honey bee hives across NSW. The fight is on to contain their spread to other states” Australian Broadcasting Corporation July 6, https://www.abc.net.au/ news/2024-07-06/states-battle-againstvarroa-mite-spread/104014530 9 Visick, O. D., & Ratnieks, F. L. W. (2023). Density of wild honey bee, Apis mellifera, colonies worldwide. Ecology and Evolution, 13, e10609. https://doi.org/10.1002/ ece3.10609. [See also, “How Many Honey Bee Colonies are There, Really?” Alison McAfee, American Bee Journal, June 2024.] 10 Rosario, C., (2018) “Greater banded hornet (Vespa tropica) established at several

locations on Guam” [poster presentation] Meeting of the Entomological Societies of America, Canada, and British Colombia, Vancouver, BC, Canada 11 And not referenced in text because it came out just after this was written, but to read the “official” paper on this: Rosario, C. A., & Miller, R. H. (2024). The health of managed and wild-living Western honey bee colonies, Apis mellifera, on Guam. Journal of Apicultural Research, 1–8. https://doi.org/10.1080/00218839.202 4.2377829

Kris Fricke is the editor of the Australasian Beekeeper, Australia’s national beekeeping magazine. He is originally from Southern California.

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