Advances in Biocontrol Are Praised At Hilo Meeting on Invasive Species

posted in: September 2019 | 1
Koa bug. USFWS

One of the oldest arguments against biological control concerns the introduction of the mongoose to Hawai‘i.

True: mongooses were introduced to Hawai‘i in the 1880s by sugar growers who believed they would knock back the problem of rats in cane fields. But since the mongoose is active during the day, while the rat is nocturnal, the two rarely crossed paths.

The mongoose is now well established on most islands in Hawai‘i, where it has done much more damage to beneficial animals, including native birds, than to the islands’ still robust rat population.

But the misguided effort hardly qualifies as an example of biocontrol gone wrong. As the Hawai‘i Invasive Species Council points out on its website, “the introduction of this species by private individuals in the sugarcane industry was not part of any scientific biological control process.

“Biological control, or biocontrol, is a robust scientific field in which research is done to identify a predator or pest of a given invasive species from its home range, followed by extensive research to determine whether the predator or pest, if introduced to Hawai‘i as a biocontrol agent, would impact only the invasive species in question. Mongoose did not undergo this evaluation prior to entry and should not be considered an example of biocontrol.”

At a two-day conference last month on invasive pests in Hawai‘i, sponsored by the Cooperative Extension Service of the University of Hawai‘i’s College of Tropical Agriculture and Human Resources (CTAHR), just how rigorous today’s biocontrol efforts have become nearly a century and a half after the mongoose experiment began was apparent in numerous presentations.

And also, just how successful.

Addressing Fears Of Non-Target Attacks

Mark G. Wright is a professor at CTAHR’s Department of Plant and Environmental Protection Sciences. His presentation, coming at the close of the conference, looked at the long history of biocontrol, going back 125 years in Hawai‘i.

While acknowledging “unfortunate errors” in the selection of some biocontrol agents as well as some well publicized instances of the biocontrol agents hopping onto non-target species, “zero non-target attacks have been recorded in the field since 1975,” Wright told the 75 or so academics, land managers, and other interested parties in attendance.

In any event, “just because something attacks a non-target doesn’t mean there’s an impact,” Wright said. One of the best- known recent examples of this occurred when the endemic, jewel-like koa bug and its eggs were attacked by two parasitoid wasps that had been introduced in the 1960s as biocontrol agents to suppress the southern green stink bug, an agricultural pest.

Citing a study by Tracy Johnson, an entomologist now working for the U.S. Forest Service in Volcano, and colleagues, Wright said that predation on koa bug eggs by one of the wasps (Trissolcus basalis Wollaston) amounted to at most 26 percent of all eggs preyed upon. That was overshadowed by far by predation by other animals (ants and spiders), which accounted for 87 percent of predation.

Predation on adult koa bugs by the other wasp, Trichopoda pilipes, was near zero at 21 of the 24 sites Johnson and his colleagues surveyed, although at three sites, with a higher density of koa bugs, predation was as high as 70 percent among adult female bugs, 100 percent among males, and 50 percent among fifth instars. “Effects of intentionally introduced parasitoids were relatively minor,” Johnson and his colleagues found.

In any case, Johnson and his colleagues wrote, “Studies of purposely introduced biological control agents should not over- shadow studies of other natural enemies; the invasion of koa bug habitats by alien keystone predators such as ants poses perhaps the greatest risk to the long-term stability of koa bug populations. Continuing habitat degradation could compound the negative effects of enemy attack.”

Still, Johnson told Environment Hawai‘i, “I would not characterize the impacts of the parasitoids on koa bugs as negligible. … [There are] a number of reasons why Trichopoda’s impacts are concerning, even though on average they measured low.”

Wright noted that today’s strict reviews of prospective biocontrol agents, much tougher than they were half a century ago, and the successes of several introductions – notably the parasitoid wasps that attacked the wiliwili gall wasp – have swayed even some of the more outspoken opponents of biocontrol.

“Classical biocontrol can contribute to conservation efforts,” he concluded, adding that it now enjoyed “substantial support from previous biocontrol opponents.”

Moving Toward Biosecurity

While biocontrol can be effective, it’s the costly pound of cure when compared with the ounce of prevention that quarantine and other biosecurity measures can provide.

In 2017, the Hawai‘i Invasive Species Council, made up of designees of five cabinet-level department heads (Agriculture; Health; Land and Natural Resources; Business, Economic Development, and Tourism; and Transportation) and the University of Hawai‘i, adopted a 10-year biosecurity plan that calls for 147 specific actions to be taken over the next decade. Seventy-five of those (51 percent) deal with preventing potential pest species from being shipped here (pre-border) or intercepting them on arrival (border). And most of those tasks fall under the jurisdiction of the state Department of Agriculture (DOA).

Randy Bartlett, interagency coordinator for HISC, outlined progress made toward the plans goals. As of last January, he said, 50 percent of them had been initiated, completed, or were ongoing in perpetuity.

Completed actions include restoration of the vector control program in the Department of Health; a relaunch of the Department of Agriculture’s detector-dog program; and development of technology needed for the first phase of an electronic manifest program for incoming cargo shipments. Work still in progress involves beefing up the restricted-plant list of the DOA; developing emergency response plans for rapid ‘ohi‘a death; addressing vessel biofouling; and finding biocontrols for miconia, Himalayan ginger, and albizia.

Altogether, Bartlett said, the state spends about $57 million a year – four tenths of a percent of its operational budget – on current biosecurity measures. If full implementation of the biosecurity plan were to occur, it would take $38.7 million a year more, and still just amount to seven-tenths of a percent of the total operational budget.

At the close of his presentation, Bartlett was asked whether all the money in the state’s “cargo inspection fund” was being used for inspection.

“I don’t think so,” Bartlett replied.

That fund – technically, the Pest Inspection, Quarantine, and Eradication (PIQE) Fund – is the recipient of a fee of 75 cents for every thousand pounds of freight brought into the state.

Under Hawai‘i Revised Statutes section 145A-4.5(b), which establishes the fund, moneys are to be used by the DOA for “the operation of biosecurity and pest inspection, quarantine, eradication, and monitoring programs,” among other things.

The state auditor reported last October that as of the close of fiscal year 2018, the fund balance stood at around $8.3 million. According to a DOA report to the Legislature last December, the department collected about $6.1 million in fees and spent around half that on personnel costs in the Plant Quarantine branch. About $3 million was spent on “other current expenses.”

Those other expenses did not, apparently, include travel to Hilo. No one from Plant Quarantine or any other division of the department attended the conference.

Status Updates

Many presentations at the conference provided updates on the status of invasive species already present in the islands.

Just two vertebrate species were addressed – the rose-ringed parakeets of Kaua‘i and the mitred conures on Maui. No four-legged animals – mouflon, deer, or feral pigs, goats, sheep, cattle, and cats – merited mention.

Conjures and Parakeets

As for the mitred conures, Adam Radford of the Maui Invasive Species Committee (MISC) said, “We’re close to getting rid of them on Maui. There used to be about 200 birds, but now we’re down to about 15 individuals.”

The fact that all of Hawai‘i’s invasive species committees are on a firearms stand-down, Radford said, meant that it was not possible for his team to use firearms to kill off the remaining birds. Efforts to capture the cliff-dwelling birds using mist nets, lures, audio playbacks, and feeding stations, or by rapelling down cliffs – have been unsuccessful, he said.

In the meantime, some of MISC’s partners, including the Department of Land and Natural Resources and The Nature Conservancy, were helping to track down the last few conures. (The ISCs and other agencies affiliated with the Research Corporation of the University of Hawai‘i have not been allowed to use firearms since late 2016, pending a review by the deputy at- torney general assigned to RCUH.)

The rose-ringed parakeets on Kaua‘i pose a different set of challenges. The bird is found in Hawai‘i on the islands of Kaua‘i and Oahu, with a nascent population on the Big Island, said Sean Siers of the U.S Department of Agriculture’s Animal and Plant Health Inspection Service, reporting on the work of Page Klug, who works out of APHIS’s North Dakota wildlife research center.

On both Kaua‘i and O‘ahu, the birds have become a major pest of agricultural crops, but on Kaua‘i, they have become a threat to public health as well, with thousands of the parakeets congregating in urban areas.

“The bread-and-butter” tool to control the birds will be firearms, Siers said. “Shooting is the only way successful eradication has occurred,” he said, citing the experience of an island in the Seychelles.

“We’re looking at protocols for a shooting campaign” on Kaua‘i, Siers said. Perhaps airguns could be used in populated areas, and shotguns employed elsewhere, but “you can’t blast every parakeet out of every tree. Most habitat is in urban areas. There’s also the fear that if you just start blasting them in urban areas, they’ll move mauka.”

Other options could include toxicants, although no registered toxicants are available, Siers added. Falconry or other predators might also be used to control the population – although, Siers noted, this is an “unlikely” option.

Jane Anderson of Texas A&M University has been engaged to do further work on ways of controlling the rose-ringed parakeet, Siers said.

Little Fire Ant

“Throw a penny anywhere in Hilo and you’ll hit six little fire ants.”

That statement, from Cas Vanderwoude – who probably knows more about the species Wasmannia auropunctata than any other living soul – may have been exaggerating, but not by much, as any Hilo resident can attest.

Vanderwoude, director of the Hawai‘i Ant Lab, described the ant as a “three-dimensional invader.” No commercial control products address it, and practically no research has been done on ants in trees, where the LFA can live. And it’s those “canopy ants,” he said, that are responsible for most of the sting incidents: “Arboreal ants that fall out of trees do most of the damage.”

The LFA is resilient. “They have an extraordinary ability to recover from our best efforts to kill them,” Vanderwoude said. “Whatever I do has a maximum impact on ants for about eight weeks.”

The species “defies efforts to control it by conventional means for three main reasons,” Vanderwoude wrote in his abstract of the presentation. These are: “an abundance of queens (more than 50 pre square meter), a remarkable ability to recover from a catastrophic event in a short time frame, and a tree-dwelling component out of reach of conventional application equipment.”

“Hawai‘i is basically screwed,” he said.

“All of Hawai‘i below 3,000 feet elevation is ideal habitat” and the ant has not begun to fill out its possible range.

A survey of literature about the ant that Vanderwoude undertook showed that as recently as twenty years ago, the LFA was practically an unknown species: “Only one paper, in 1997, talked about the little fire ant as potentially invasive.”

Vanderwoude found just 341 papers on the little fire ant, fewer than 40 of which were relevant – and just 11 of those talked about control or impacts.

By comparison, there were 2,975 papers on Solenopsis invicta, the red imported fire ant.

The little fire ant was first detected on the Big Island in 1999. Since then, it’s spread all over the island and now has been found on Maui, O‘ahu, and Kaua‘i, where efforts to limit the spread of the ant continue to be made.

Key hub ports in the Pacific – in Hawai‘i, Guam, Tahiti, and Fiji – are now all infested, Vanderwoude said, “and this will most likely lead to the continued spread of this species.”

Vanderwoude’s lab has developed baits that can be applied aerially and other means of addressing the problems associated with LFA infestation. The lab’s outreach arm works with large landowners, farmers, and others to help in developing management strategies.

Rat Lungworm

Little fire ants are, as the name suggests, pretty small – about a millimeter and a half in length. Line up a hundred of them, end to end (pretty easy to do in Hilo), and the line will be around six inches long.

By contrast, the rat lungworm, An- giostrongylus cantonensis, is microscopic. Yet once in humans, it can cause devastating health effects, even death.

As Sue Jarvi of the Daniel K. Inouye College of Pharmacy at the University of Hawai‘i-Hilo explained, humans are an accidental host, along with dogs, horses, and other animals. The rat lungworm’s life cycle ideally involves snails or slugs, which are intermediate hosts, to rats.

Rat lungworm has been known to be in Hawai‘i for decades, but human infections were relatively rare until recently. Many have linked its spread to the arrival of the Asian semi-slug, which carries many times more rat lungworm larvae in its tissue than other snails and slugs. The semi-slug was not found on Hawai‘i island until 2004, but it has spread widely since then, particularly in the Puna district.

In East Hawai‘i island, 94 percent of rats tested were found to be infected with rat lungworm, while 70 percent of the semi-slugs were infected. Even a tiny piece of an infected snail can contain hundreds of larvae.

Larvae can live outside of snails or slugs and can be transmitted to humans in a variety of ways. Eating unwashed produce or snails can lead to infection, but also drinking water from catchment systems where larvae-carrying mollusks have fallen in. According to Jarvi’s research, live and infective larvae emerge from drowned slugs or snails within three or four days, and they can survive on their own in the water for at least three weeks.

Since most of the larvae sink, answering the question of what filters are effective in trapping the larvae is important for Puna residents on catchment. Just one of the five commercially available sediment filters proved effective in intercepting all larvae: the Matrikx Accucarb, which uses a carbon block filter. An ongoing study in Jarvi’s lab suggests that ultraviolet light systems, employed by many Puna households, may not immediately kill all larvae.

Another daunting problem in the treatment of rat lungworm infection has been diagnosis. Up to now, a definitive diagnosis involves a spinal tap. Jarvi and her colleagues are now working to develop a blood-based diagnosis, which would make diagnosis much simpler.

Rapid ‘Ohi‘a Death

Researchers and foresters are learning ever more about the ways in which two Ceratocystis fungi – C. lukohia and C. huliohia – work once they infect ‘ohi‘a trees.

Mark Hughes of the University of Hawai‘i’s College of Tropical Agriculture and Human Resources described the different mechanisms. The former, which is more quickly fatal to infected trees, is a wilt disease, with the fungus migrating through the tree’s vascular system even before symptoms – dying crown, dead leaves – become visible.

In the case of C. huliohia, the disease causes cankers, which eventually spread and join up with other cankers.

Robert Peck of the Hawai‘i Cooperative Studies Unit at the University of Hawai‘i- Hilo, discussed the role ambrosia beetles play in spreading both diseases. Frass from the beetles, caused when they clear out the tunnels they bore in the trees, can carry the spores of Ceratocystis. Those spores, he noted, are sticky and while not able to become windborne on their own, they can attach to frass. Peck and his colleagues found viable fungus in frass from the very tops of some trees.

Some of the frass that was collected in environmental samplers showed “fungal structures,” he noted, but none were viable in the lab. Peck was asked whether the long residence time in the samplers – up to several weeks – might have caused the spores to dry out and die. Peck acknowledged that possibility, and said more frequent monitoring of the samplers might be needed.

J.B. Friday, extension forester with the University of Hawai‘i-Hilo, noted that research is being done to identify ‘ohi‘a that might be resistant. Also, in very limited circumstances, where a single tree is highly valued, treatment with a fungicide might keep a tree healthy.

But in the meantime, more than a million ‘ohi‘a trees have died as a result of rapid ‘ohi‘a death, and more than 170,000 acres of native forests have been affected on Hawai‘i island alone, he noted. “Island-wide eradica- tion is out of the question,” he said.

Yet much can be done to halt its spread, he said. Quarantine of untreated ‘ohi‘a products from Hawai‘i island, washing of trucks and tools, cleaning of boots and gear – all will help in stopping the spread of ROD.

Equally important, if not more so, is the need to reduce wounding of ‘ohi‘a trees. “You need a wound for infection to occur,” he said. To underscore this point, he dis- played a map showing ROD-infected trees in the Kahuku area of Hawai‘i Volcanoes National Park. “Kahuku has 60 (ROD-) positive trees,” Friday said. “All are below the fenceline” that surrounds the ungulate-free area.

A similar map showed the park’s Ola‘a tract, near Volcano Village. Again, in the ungulate-free fenced area, no infected trees are found.

“Fencing, removing the ungulates, protects the forests,” he said. “We need to protect what’s healthy rather than restore what’s lost,” he concluded. “We don’t want to go the dry-forest way.”

—Patricia Tummons

One Response

  1. And just because the studies haven’t been done to examine the non-target impacts of these “safe” biocontrols doesn’t mean there aren’t any.

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