biocontrol — Maui Invasive Species Committee (MISC)

Safe biological controls rely on specialized species

Posted on March 19, 2021 by Lissa Strohecker

Living creatures can be grouped as specialists or generalists based on their strategies for finding food and habitat: generalists thrive in a variety of conditions and eat a range of foods; specialists rely on a particular environmental condition or a food type. For example, specialist species like koalas only eat eucalyptus leaves, Kamehameha caterpillars rely on māmaki, and our iconic ʻāhinahina (silverswords) are found only in high-elevation alpine environments in Hawaiʻi.

When researchers look for a biological control agent – another living species that can be used to reduce a pest – they look for specialist species. This is part of an approach that began over 40 years ago with the goal of reducing unintended impacts. It works. Since 1975, over 50 different biological control agents have been brought into Hawaiʻi. “There have been no unpredicted non-target impacts in that time,” says Darcy Oishi, the Biological Control Section Chief at the Hawaiʻi Department of Agriculture. He oversees the efforts to find, test, and release biological control in Hawaiʻi.

“We worry most about specificity,” says Oishi. Host-specificity, the relationship between the pest and the natural enemy, is the creed of modern biological control. By seeking out species that have evolved to be dependent on the target host, there is less risk that the natural enemy will have unintended consequences.

Wiliwili are endemic to the Hawaii Islands and are a keystone species in the dryland forest. Photo courtesy of Forest and Kim Starr

As new pests arrive in Hawaiʻi (and sometimes even before), the Hawaiʻi Department of Agriculture compiles lists of possible natural enemies, specialist species that could act to lessen the invasiveness and impacts of the pest in Hawaiʻi. Scientists comb through the scientific literature, call and visit natural history museums, and consult with entomologists and researchers worldwide, learning what species live in close association with the pest in its native habitat.

Exploratory entomologists then travel to the pest’s native range to collect candidates. Each potential natural enemy is studied further in its host range. After ruling out potential candidates, entomologists collect several species for additional testing.

Back in Hawaiʻi, the biological control agents are quarantined, raised and tested again for host specificity. In a process called no-choice testing, a potential agent is evaluated throughout its life stages to see if It will eat species it is likely to encounter in Hawaiʻi. For example, in introducing a biocontrol for a plant, the agent is isolated with other non-target plants to find out whether any unintended plants could be affected.

Researchers evaluate host specificity by looking at genetically related species as well as unrelated species that evolved similar characteristics to the target. For example, pasture-invading fireweed is in the aster family, but the phytoalkaloid – the toxic chemical that sickens animals – is what attracts one natural enemy, a caterpillar, to the plant. The caterpillar is tested to see if it can feed on related plants in the Aster family as well as those containing a similar toxic chemical.

Fireweed, *Senecio madagascarensis,* is a pasture invading pest that contains a chemical poisonous to horses and cattle. Photo by Forest and Kim Starr.

Until the 1970s, biocontrol agents were selected primarily based on the impact they would have on the pest, an approach that has unfortunately biased people against biological control today. Since then, though, rigorous selection and testing has gone into preventing unintended consequence. Another challenge is caused by misinformation; some invasive pests are inaccurately equated with biological control. For example, ʻōhiʻa rust, a leaf fungus that threatens our native ʻōhiʻa, decimated populations of rose apple, leading some to inaccurately assume it was an intentional introduction; instead, it was another of the thousands of unwanted pests that arrive in Hawaiʻi accidentally.

Modern biological control provides long-term, cost-effective, environmentally safe control of invasive species. It’s an essential tool in protecting Hawaiʻi from the impacts of widespread invasive species. Biological control does not eradicate a pest; it balances the equation to lessen the harm. The biological control for prickly pear cactus hasn’t eradicated it; the plant is still here, but instead of blanketing upcountry pastures it occurs in patches. Biological control saved the wiliwili trees of Hawaiʻi from decimation by a leaf gall wasp. The problem-causing wasp is still here but does less damage with the biological controls working to keep it contained.

Take time to learn more about biological control in Hawaiʻi and contribute to the decision-making process. Visit the Department of Land and Natural Resources biological control page at https://dlnr.hawaii.gov/hisc/info/biocontrol/

Lissa Strohecker is the public relations and education specialist for the Maui Invasive Species Committee. She holds a biological sciences degree from Montana State University. Kia’i Moku, “Guarding the Island,” is prepared by the Maui Invasive Species Committee to provide information on protecting the island from invasive plants and animals that can threaten the island’s environment, economy, and quality of life.

This article was originally published in the Maui News on May 9, 2020 as part of the Kia‘i Moku Column from the Maui Invasive Species Committee.

Tiny golden butterfly could help halt miconia invasion

Posted on April 28, 2020 by Lissa Strohecker

Caterpillars of the golden miconia butterfly can only survive on miconia and related plants. The caterpillars get together in clumps and devour the leaves. In doing so, they may reduce the damage miconia can cause in the rainforest. — PABLO ALLEN photo

In the hills above Hāna, Nāhiku, and Keʻanae, the Maui Invasive Species Committee (MISC) crew hikes day in and day out looking for and pulling miconia plants. The team is about to grow as a kaleidoscope of golden yellow butterflies descends to assist with control.

Miconia is a notorious invader of Hawaiian forests. A single plant can produce 8 million seeds. Miconia seeds grow quickly into large plants with huge leaves that block out the sunlight preventing other plants from germinating. Miconia’s shallow roots do little to stabilize the soil. Eventually, miconia becomes the only plant in the forest; invaded sites are known for landslides and erosion that muddies streams and buries reefs.

Sam Akoi III pulls miconia from the ground in 2003. The shallow roots make the plant easy to pull but miconia does a poor job holding soil. Invaded forest slopes are prone to erosion–MISC file photo

When biologists first found this invasive plant growing in Hawaiʻi, it was a call to action. Retired state forester Bob Hobdy helped address miconia in East Maui in the early 1990s. Initially, crews focused on the area above Hāna known as “the core,” but reports started pouring in from multiple locations across East Maui. “The idea of eradication [removing every plant from the island] was set aside,” says Hobdy. “It was not feasible.” The shrubby tree was scattered from Huelo to Kipahulu, with two major infestations in Nāhiku and Hāna. Too widespread to eradicate, but too damaging to ignore, the long-term solution was biocontrol: the researched introduction of a natural enemy specific to miconia that could lessen the impact and spread of the plant.

Over the last 27 years, crews have worked to contain this invader in the field. It’s been a success: miconia never reached the West Maui mountains and it’s rare to find a plant along Hāna Highway. Meanwhile, researchers in Hawaiʻi and South America have sought out and tested insects and plant diseases in hopes of finding something that will permanently undermine the plant’s invasiveness.

In 1997, ecologists released a fungus that eats holes in miconia’s large purple leaves. In Tahiti, this fungal natural enemy opened up the canopy so that other plants could grow, but fungus didn’t have the same effect here in Hawaiʻi. The search continued.

Tracy Johnson of the U.S. Forest Service has worked to find miconia’s natural enemies for 20 years. He’s hopeful about another miconia pests, a tiny yellow butterfly that lays its eggs on the leaves. The caterpillars hatch out and to dine on the umbrella-like leaves until they become adults. “Itʻs very specific to miconia,” says Johnson. “We know from observation in Costa Rica and in Hawaiʻi that it’s one of the most damaging insects to leaves of the plant.”

Miconia’s huge leaves are major problems: they act like tarps, shading out the understory, collecting raindrops and funneling them to the ground. In comparison, native ōhiʻa and koa trees have clusters of little leaves that break up rainfall into small drops that gently water the understory. The raindrops that roll off of miconia leaves are some of the largest measured They hit the ground with extra force—and since the ground beneath miconia is bare—they contribute to increased erosion. In fact, scientists have found that erosion is greater in a miconia-invaded forest than if the rain fell on bare soil.

“Itʻs (the golden miconia butterfly) very specific to miconia,” says Johnson. “We know from observation in Costa Rica and in Hawaiʻi that it’s one of the most damaging insects to leaves of the plant.”

Though only the size of your fingernail, the golden miconia butterfly could have a big impact on invasive miconia. Native to Costa Rica, these butterflies could be a welcome addition to miconia control efforts here in Hawaiʻi. — KENJI NISHIDA photo

Enter the golden miconia butterfly, Euselasia chrysippe, —a voracious leaf eater. Johnson and colleagues from the University of Costa Rica tested E. chrysippe with 73 different plants to see what the caterpillars would feed on. In a process called no-choice testing, caterpillars are placed in a petri dish with a leaf of the plant being tested. When forced to feed on other plants, they died; only Miconia calvescens and closely related plants in the melastome family can sustain them. This is good news since Hawaiʻi has no native melastomes.

After gorging on miconia, E. chrysippe caterpillars metamorphose into butterflies and seek out another miconia plant on which to lay their eggs. Like the MISC miconia crews, they’re really good a finding the pesky plant.

The golden miconia butterfly could help halt Hawaiʻi’s miconia invasion. But there is still more to be done. Johnson is investigating other potential natural enemies, particularly an insect that eats miconia seeds. Until a suite of effective and safe natural enemies exists to control miconia, crews from MISC will continue combing the hillside in search of miconia. Any sightings of miconia can be reported to MISC at 808-573-6472.

April 2020 Update: The Hawaiʻi Department of Agriculture is soliciting comments on the draft Environmental Assessment for the release of the golden miconia butterfly. Comments are accepted through May 26, 2020. HDOA press release

This article was originally published in the Maui News on July 8th, 2018, as part of the Kia‘i Moku Column from the Maui Invasive Species Committee.

Natural enemies could tame invasive Himalayan ginger

Posted on June 5, 2018 by Lissa Strohecker

Though not invasive in India where it is native, Himalayan ginger can completely transform a Hawaiian rainforest like it has in this section at 4,000-foot elevation above Haiku. Inset: Ginger fruits are spread long distance by birds and rats. FOREST and KIM STARR photo

The subtropical rainforests in the foothills of the Himalayan Mountains are amazingly diverse. In sections of India and Nepal, the forests are similar to Hawaiian rainforests in both temperature and rainfall-but the flora and fauna are radically different: this is the land of elephants and red pandas; 600 species of butterflies live here and over 400 species of orchids. But amongst the exotic plants there is one

The fruit of Himalayan ginger is a tasty treat for non-native birds, but this means the seeds are spread throughout the forest. Photo courtesy of Forest and Kim Starr.

that might be familiar to residents of Hawai’i-a yellow-flowered ginger that covers vast sections of Hawaiian rainforests.

Himalayan ginger, Hedychium gardnerianum, is native to the Himalayan foothills. There, it evolved over millennia supporting a diversity of species: the sweet nectar is a food for the long-tongued butterflies of the region and the plant lives in harmony with the species that surround it. Yellow flower stalks dot the landscape amongst hundreds of other orchids, gingers, ferns, and trees.

But in Hawai’i, Himalayan ginger dominates the landscape-growing fast and paving its way into the forest in an unrelenting march.

“Himalayan ginger displaces critical native vegetation layers, limits canopy tree recruitment, and hogs water resources in their massive rhizomes (roots). As it takes over and forms monotypic stands, it negatively impacts native flora and fauna, including Hawai’i’s unique arthropod complex and the Hawaiian honeycreepers,” says Alison Cohan, director of the Maui Nui Forest Program with The Nature Conservancy (TNC).

Introduced as an ornamental, Himalayan ginger escaped backyards and began invading rainforests of East Maui in the mid 1950’s. With seeds dispersed far and wide by birds and rats, the weedy plant spreads by leaps and bounds into the forest. Today, much of the mid-elevation rainforest of East Maui is a patchwork of native forest and alien ginger. But there is a lot left to protect: many ginger-free areas remain, including most of West Maui.

Ginger is a formidable foe and removing the plant is no simple task. Roots pave the forest floor like asphalt and every part of the rhizome must be removed. Bagged rhizomes take years to decay and if there is the slightest hole in the bag, hardy shoots emerge. If using herbicide, every portion of the root has to be treated. Plants on steep slopes and cliffs are inaccessible and impossible to remove until the weight of the water-logged roots causes entire sections to collapse in a landslide.

Why would ginger be a pest in one place but not another?

Djami Djeddour, weed biocontrol scientist with the Centre for Agriculture and Bioscience International, inspects a lone Himalayan ginger plant in India while searching for insects and fungi that live on the plant where it is native. These insects may be responsible for keeping the plant in check. DJAMI DJEDDOUR photo

The answer to that question is on the minds of resource managers in Hawai’i as well as New Zealand, Australia, and South Africa where the plant is invasive. With funding from organizations like TNC and the Hawai’i Invasive Species Council, research scientists traveled to India and collected insects and fungi that live on Himalayan ginger hoping to discover what keeps the fast-growing herb in balance there. An effective natural enemy could be a game changer for Hawai’i.

An effective natural enemy wouldn’t eliminate the plant, just bring it into harmony with the surrounding environment, much like it is in India and Nepal.

One of the most promising insects is a Cloropid fly that lives only on Himalayan ginger. The larvae live inside the stem stunting the growth and reducing flower production. Ginger natural enemies may be ready for release in New Zealand soon, promising progress for Hawai’i.

“The Nature Conservancy had been doing ginger work in Waikamoi for over 30 years, systematically conducting ginger control—containing the core population at the western edge of Waikamoi and eradicating outliers in native forest,” explains Cohan. Crews with Haleakala National Park work on the flowering pest in Kīpahulu Valley but the plant is widespread and thrives unchecked in wet places throughout the state.

There are ways you can help. Consider what you call the plant: though known for years as kāhili ginger, a pest destroying the rainforest does not deserve a moniker reminiscent of Hawaiian royalty much less one that might suggest that it belongs here. Perhaps call it toilet-brush ginger, as suggested by Pat Bily of TNC after years of removing it. Do not plant Himalayan ginger in your yard and remove it from your property before it spreads. Finally, participate in The Nature Conservancy’s quarterly volunteer trips removing ginger from Waikamoi Preserve. Contact hike_waikamoi@tnc.org if interested.

This article was originally published in the Maui News on April 8th, 2018 as part of the Kia‘i Moku Column from the Maui Invasive Species Committee.

Natural enemies could tame invasive Himalayan ginger

Posted on April 23, 2018 by Lissa Strohecker

Though not invasive in India where it is native, Himalayan ginger can completely transform a Hawaiian rainforest as it has in this section at a 4,000-foot elevation above Haiku. Ginger fruits can be spread long distance by birds and rats. — FOREST and KIM STARR photo.

Himalayan ginger, Hedychium gardnerianum, is native to the Himalayan foothills. There, it evolved over millennia supporting a diversity of species: the sweet nectar is feed for the long-tongued butterflies of the region and the plant lives in harmony with the species that surround it. Yellow flower stalks dot the landscape amongst hundreds of other orchids, gingers, ferns, and trees.

But in Hawai’i, Himalayan ginger dominates the landscape-growing fast and paving its way into the forest in an unrelenting march. “Himalayan ginger displaces critical native vegetation layers, limits canopy tree recruitment, and hogs water resources in their massive rhizomes (roots). As it takes over and forms monotypic stands, it negatively impacts native flora and fauna, including Hawai’i’s unique arthropod complex and the Hawaiian honeycreepers,” says Alison Cohan, director of the Maui Nui Forest Program with The Nature Conservancy (TNC).

Djami Djeddour, weed biocontrol scientist with the Centre for Agriculture and Bioscience International, inspects a lone Himalayan ginger plant in India while searching for insects and fungi that live on the plant where it is native. These insects may be responsible for keeping the plant in check. — DJAMI DJEDDOUR photo.

Introduced as ornamental, Himalayan ginger escaped backyards and began invading rainforests of East Maui in the mid-1950s. With seeds dispersed far and wide by birds and rats, the weedy plant spreads by leaps and bounds into the forest. Today, much of the mid-elevation rainforest of East Maui is a patchwork of native forest and alien ginger. But there is a lot left to protect: many ginger-free areas remain, including most of West Maui.

Invasive Himalayan ginger taking over the east side of Maui. Ginger fruits can be spread long distance by birds and rats. — FOREST and KIM STARR photo.

An effective natural enemy wouldn’t eliminate the plant, just bring it into harmony with the surrounding environment, much like it is in India and Nepal. One of the most promising insects is a Cloropid fly that lives only on Himalayan ginger. The larvae live inside the stem stunting the growth and reducing flower production. Ginger natural enemies may be ready for release in New Zealand soon, promising progress for Hawai’i.

“An effective natural enemy wouldn’t eliminate the plant, just bring it into harmony with the surrounding environment, much like it is in India and Nepal.”

“The Nature Conservancy had been doing ginger work in Waikamoi for over 30 years, systematically conducting ginger control—containing the core population at the western edge of Waikamoi and eradicating outliers in native forest,” explains Cohan. Crews with Haleakalā National Park work on the flowering pest in Kīpahulu Valley but the plant is widespread and thrives unchecked in wet places throughout the state.

This article was originally published in the Maui News on April 3rd, 2018, as part of the Kia‘i Moku Column from the Maui Invasive Species Committee.

A possible solution for the weedy tibouchina

Posted on February 13, 2018 by Lissa Strohecker

The upper elevations of the West Maui mountains are home to unique plants and animals found only here. Among them, species of lobelia and dwarf ʻōhiʻa. Tibouchina is one of the persistent threats to the survival of these rare species. Photo by Lissa Strohecker.

Tucked away in the rain and fog of the West Maui mountains are uniquely Hawaiian treasures: high-elevation bogs carpeted by rare and restricted plants. The last few hāhā (Cyanea magnacalyx) existing in the wild anywhere in the world are found there. Dwarf ʻōhiʻa, two unique silverswords, and many other plants are restricted to the high summit bogs and have adapted to the wet substrate.

Conservation crews monitor these bogs closely–they are in a section of West Maui that is fenced and protected from pigs, goats, and deer. Nonetheless pinhead-sized seeds of invasive cane tibouchina (Tibouchina herbacea) blow into the bog from the lower elevations and threaten the fragile ecosystems.

If crews did not remove tibouchina, it would take over the bog, crowding out the Cyanea and other endangered plants. It’s only in these ecologically sensitive bogs that crews remove tibouchina–there is simply too much of it on the surrounding slopes. As a result, it’s a continuous battle.

“Tibouchina is scattered throughout the 50,000 acre watershed of the West Maui. It’s found from sea level to the summit of Puʻu Kukui, but thrives in the wet windward slopes between 2,000-4,000 feet,” says Chris Brosius, manager of the West Maui Mountain Watershed Partnership. His crew helps to protect the bogs along with the rest of the watershed.

“West Maui is the steepest land area in the state, more dissected by cliffs than any other watershed in the Hawaiian Islands,” says Brosius. Even if they had the capacity, “We couldn’t possibly control this species everywhere it grows.”

Tibouchina thrives where there is soil disturbance–whether from pigs or the landslides that helped shape the West Maui’s. Tibouchina is often the first plant to arrive after a landslide.

Tibouchina belongs to the melastome family, a group of plants that are notoriously invasive in Hawaiʻi–miconia and clidemia are both melastomes. An ugly second-cousin to miconia, tibouchina is often leggy and scruffy looking. The leaves are two inches long, fuzzy, and lack the purple underside that characterizes miconia; the purple flower is pretty, but small–unlike the closely related glory flower.

A member of the melestome family, tibouchina is a notorious invader thatʻs past the stage of containment. Photo by Forest and Kim Starr.

Biologists first noticed tibouchina in 1977 on Big Island and in 1982 near Waiheʻe Ridge on West Maui. Within a few years it had spread throughout Maui, Lānaʻi, and Hawaiʻi Island. By 2005 it was found on Oʻahu, likely introduced on dirty hiking boots. It has shown up on Molokaʻi as well. As a trailside weed, it can be problematic–hikers passing through a patch of tibouchina end up coughing as tiny hairs are knocked off and the plant can be a skin irritant.

Tibouchina is native to Brazil. It can be difficult to find there–occasionally appearing in wet areas and meadows. It only reaches three feet in height and dies back every year. But here in Hawaiʻi, tibouchina can be 9-12 feet high. When last year’s growth dies back, the plant re-sprouts from the roots, creating bamboo-like thickets and taking over habitat for native species.

Why would the plant behave so differently here? One explanation is the lack of predation. Tibouchina evolved in Brazil alongside insects that munch its leaves, seeds, and roots. These insects are not present in Hawaiʻi, so tibouchina grows and spreads unchecked. One of tibouchina’s natural predators is a small beetle–both the larvae and the adults devour tibouchina leaves.

The beetle, called Syphrae uberabensis, can only survive by eating tibouchina and select other melastomes, none of which are native to Hawaiʻi. After 20 years of work collecting and evaluating the beetle’s impacts on other species in quarantine, US Forest Service scientists are confident that the beetle poses no negative threat and are preparing to release it into the wild.

An insect that relies on tibouchina for survival is in the final stages of evaluation for release in Hawaii. The syphrae beetle could make tibouchina less invasive. Photo by Forest and Kim Starr

The syphrae beetle could be what takes tibouchina down a notch–reducing the threat it poses to the remaining habitat of Hawaiʻi’s rarest native plants and animals. “If we don’t intervene, this species will continue to encroach on high-value native areas, erode biodiversity and spread elsewhere in the state,” says Brosius.

Tibouchina is just one example of a widespread pest with dramatic impacts. You can help by cleaning your hiking and hunting gear to prevent spreading hitchhiking pests.

This article was originally published in the Maui News on January 14th, 2018 as part of the Kia‘i Moku Column from the Maui Invasive Species Committee.

Moving on from the Mongoose: the Success of Biological Control in Hawai‘i

Posted on April 18, 2012 by Lissa Strohecker 2 Comments

Achieving balance–in your workplace, at home, on your surfboard, or with your checkbook—makes life manageable. Natural environments depend upon balance as well.

Invasive pests have been disturbing the natural balance of Hawaiian ecosystems for centuries, ever since the arrival of the rat with early Polynesian explorers. Bringing invasive species into better balance with the environment is nothing new here in Hawai‘i. An effective biological control, or natural predator, can transform a devastating invasive species into a mild pest.

The invasive Erythrina gall wasp that threatened the native wiliwili trees, such ans this one, was brought into balance by a parasatoid wasp.

The vast majority of biological control efforts in Hawaii have been successful: pānini cactus that once choked pasture land is now checked by three predatory insects and a plant fungus; white loosestrife or pāmakani is continually attacked by two insects and another plant fungus; and recently, the Erythrina gall wasp, that wiped out ornamental coral trees and threatened the native wiliwili with extinction, was leveled by a parasitoid wasp.

Yet, just as impulsive actions sabotage balance in our own lives—think diet fads and over-exercising–the same kind of recklessness results in greater instability in our environment.

Such is the case with the small Indian mongoose, Herpestus javanicus. In 1872, a sugar planter released nine mongoose on Jamaica with the hope it would control rats in cane fields. The planter considered it successful and published a paper about it. Mongoose populations grew and offspring were sold to plantations throughout the Caribbean, Cuba, and Puerto Rico. In 1883, Hawai‘i plantation owners jumped on the mongoose bandwagon. With little regard for potential impacts, the now defunct Hilo Planters Association released seventy-two mongoose from Jamaica in Hilo. Another batch of mongoose from eastern India was brought to the Hāmākua coast in 1885. Subsequent offspring were released on Maui, O‘ahu, and Kaua‘i. For an unknown reason the crate delivered on Kaua‘i was kicked off the dock. To date mongoose have not established on Kaua‘i, though a single female was found killed by a car in 1972.

The mongoose is an opportunistic predator, introduced to Hawaii in 1883 with little regard to potential impacts on species other than the rat. Today, a potential biological control goes through years of testing to ensure it will have no unanticipated impacts.

Mongoose do eat rats, in Hawai‘i and elsewhere, but mongoose are opportunistic predators eating primarily insects, with birds, eggs, and a handful of plants mixed in. Additionally, mongooses are active during the day, rats at night. The introduction of the mongoose further tipped the balance of the environment in the wrong direction: now both mongoose and rats threaten populations of native birds, particularly ground-nesting species like nēnē and petrels.

The mongoose introduction was not an example of classical biological control; it was an impulsive, untested whim. Today, when researchers look for biological controls for a particular pest, they survey the pest’s native habitat for species that counteract the pest’s invasive characteristics. Before any new organisms are introduced in Hawai‘i, they are subjected to intensive testing in quarantine to determine potential impacts on any other species.

Successful candidates for biological control have evolved over millennia alongside their target; some are dependent solely on the target species for survival. For example, the Eurytoma wasp that saved the wiliwili will die without access to Erythina gall wasps. Consequently, Eurytoma populations will stop short of entirely eliminating the Erythrina gall wasp. Rather it will restore balance, keeping the pest wasp in check.

When mongoose were brought to Hawai‘i, there were no restrictions on plant and animal imports. Impacts on other species were an afterthought, if considered at all. It wasn’t until King David Kalākaua enacted the “Laws of the Hawaiian Islands” that any regulation existed to limit the introduction of new species to Hawai‘i.

Government-led pest management didn’t begin until ten years after sugar growers introduced the mongoose. The provisional government appointed Albert Koebele as the chief entomologist, the first of many tasked with preventing new and controlling existing pest populations

Biological control has a long and successful history in Hawai‘i. In fact, California and Hawai‘i lead the world in successful releases of natural predators. Ever since testing of biological controls began, there have been no incidences of “host-jumping” or biological controls attacking other species. Yes, the infamous mongoose ran amok, but it arrived during an “anything goes” era in Hawaiian history. The mongoose–or any opportunistic predator–would never be considered suitable for introduction by today’s standards. Biological controls are an important tool—sometimes the only tool—that can restore balance in Hawaiian ecosystems.

Originally published in the Maui News, April 8th, 2012 as part of the Kia‘i Moku Column.
You can find all the articles in the Kia‘i Moku series http://www.hear.org/misc/mauinews/

Biocontrol precision is weapon against invaders

Posted on September 6, 2011 by Lissa Strohecker Leave a Comment

Lloyd Loope

Last month I began to present my point of view as a conservation scientist relevant to current “controversy” over biocontrol of strawberry guava (Psidium cattleianum), Hawaii’s most damaging invasive plant species. I touched upon the generally accepted theory that many highly invasive plant species, held in check by insects and pathogens in their home range, become unbeatable competitors in their introduced range where those insects and pathogens are lacking. Strawberry guava exemplifies the “enemy release” theory; it is attacked by virtually no insects or pathogens wherever it invades on many tropical islands of the world.

Though I’ve always supported the concept of biocontrol as a potential tool for Hawaii’s most widespread and most invasive plants, I recall a personal pessimism in the 1980s that biocontrol success might be unlikely in this case because guava is in the myrtle family (same as Hawaii’s ‘ōhi‘a) and commercially important common guava (Psidium guajava) is such a closely related sister species.

A strawberry guava tree in Curtiba, Brazil is heavily infested with the galls of the scale insect Tectococcus ovatus. This is the typical effect of the insect on the plant. It was a result of a naturally developing infestation of the insect in the plant’s native range. U.S. Forest Service photo

But state and federal natural resource agencies in Hawaii have managed to cobble together a remarkably stellar program to address the rampant invader. In 1991, the National Park Service and the University of Hawaii began to collaborate with the Federal University in Curitiba, Brazil, to identify and evaluate potential biocontrol agents. After 10 years of field observations and other testing working within the native ranges of both strawberry guava and common guava in Brazil researchers found 133 insect species in 12 orders and 80 families that fed on strawberry guava. Thirty-one of those species fed only on plants in the myrtle family, and five species fed only on strawberry guava and not at all on common guava. The collaborative program zeroed in on Tectococcus ovatus, a scale insect that feeds on the new growth, creating galls on the leaves of strawberry guava. This scale insect was the choice for more intensive work based on the relative severity of damage inflicted on P. cattleianum and the ease of handling it.

Tectococcus ovatus was brought to containment facilities in Hawaii and Florida, where strawberry guava is also invasive, for intensive experimental testing to ensure its safety as a biocontrol agent. Many related native and non-native plants were tested as potential host species. Strawberry guava is the only plant in Hawaii that this insect is able to feed on. Dr. Tracy Johnson of the U.S. Forest Service in Hilo has brought the program close to fruition over the past eight years.

The insect reduces the plant’s energy and nutrients available for growth and reproduction. Heavy infestation is expected to accelerate leaf drop and reduce fruit and seed production. Some fruit will be produced and the plants are not expected to die. If the scale insect thrives, it will level the playing field between the invasive strawberry guava and native forest species.

What other species in the ecosystem will be affected by the expected decline in strawberry guava fruit production? Feral pigs and a few species of non-native birds will lose a seasonal carbohydrate diet supplement during the September-December fruiting season. These same species are fully able to thrive in areas where there is no strawberry guava.

Hawaii is confronted by intractable invasive species problems, but by integrating prevention, early detection, rapid response, and biocontrol we can begin to address these problems. Biocontrol is an essential part of invasive plant management strategies in New Zealand, Australia, and the U.S. mainland. Florida has become a leader in biocontrol in the past decade. For example I recently learned that thanks to two insects introduced about 10 years ago as classical biocontrol agents, the notorious Melaleuca, or paper bark tree is no longer invasive in the Florida Everglades! My scientific opinion is that biodiversity conservation in Hawaii will not succeed without the enlightened use of biological control.

Lloyd Loope is a research scientist with the U.S. Geological Survey stationed at the Haleakala Field Station. He holds a doctorate in botany from Duke University and is an active Maui Invasive Species Committee member.

Originally published in the Maui News, October 12, 2008 as part of the Kia‘i Moku Column.
You can see all the articles in the Kia‘i Moku series http://www.hear.org/misc/mauinews/

Strawberry guava sows seeds of infestation

Posted on August 30, 2011 by Lissa Strohecker 1 Comment

The fruit if strawberry guava are eaten by birds that spread the tiny seeds. Photo by Forest & Kim Starr

When I came to Maui 28 years ago to work as a research biologist at Haleakala National Park, one of the first things I learned was that strawberry guava (Psidium cattleianum) was regarded as the most damaging invasive plant in the state. A year later, I was in Kipahulu Valley and experiencing the amazing guava fruiting and dispersal season. The 10-30 foot tall trees left a sea of red fruits that still lurks in my memory. There were dense, extensive guava thickets of tens of acres at the 2,000-3,000 ft elevation level in the valley. One could scarcely walk through; there were literally no other species present. These devastated areas contrasted sharply with the rich biodiversity in nearby areas with intact native understory vegetation.

A dense infestation of strawberry guava, or waiawī , in the Makawao Forest Reserve. Photo by Forest and Kim Starr

At that time, C.H. Diong, a graduate student at UH-Manoa, was putting the final touches on his Ph.D. thesis. Diong showed that feral pigs had been the primary agent spreading strawberry guava from the mouth of the valley upslope for the past 30 years or so. The pigs fed almost exclusively on guava fruits during September-December. The seeds pass through the pigs’ digestive tracts with no loss of viability. Fruiting was occurring only below about 3000 ft elevation but the seeds could germinate and grow much higher, up to over 4000 ft in the valley.

Years later, my colleague Dr. Art Medeiros did his Ph.D. thesis on the biology of weeds in Kipahulu Valley and East Maui. Art estimated that strawberry guava already occupies over one-third, or 8900 acres, of its potential area of dominance on East Maui. Although feral pigs had been eliminated and fenced from Kipahulu Valley since the late1980s, Art found that non-native birds, primarily the red-billed leiothrix, were also spreading strawberry guava seeds. Strawberry guava plants were still not fruiting above 3000 ft, but seeds planted experimentally (or those carried by birds or pigs) germinate at much higher elevations. Strawberry guava now reaches as high as 5300 ft on East Maui in at least one location.

Strawberry guava has infested the outlined area on Mahana Ridge, just to the east of Honokahua Valley in West Maui. Photo by Randy Bartlett.

Newly established guava plants can spread vegetatively by root sprouts. On all the major islands, nearly monotypic guava stands infest thousands of acres of moderately wet (mesic) and very wet forest. Strawberry guava is considered a serious threat to native forests due to its ability to invade relatively undisturbed areas and form thickets with dense mats of feeder roots. Dense invasion allows only about 5% of sunlight into the understory. The guava at first invades under native canopy, then expands and closes the mid-level canopy position, preventing the establishment and regeneration of all other species, including the dominant native forest plants – ohia and koa. Although it continues to expand into relatively pristine native forest areas, strawberry guava is now so widespread in Hawaii that its future impacts are expected to consist mainly of filling in areas creating monotypic stands.

As one of the founding members of the Maui Invasive Species Committee, I never considered taking on strawberry guava as a MISC target given its wide distribution and abundance and MISC’s limited resources. We always hoped for the eventual possibility of identifying an effective biological control.

A generally accepted theory of biological invasions is that certain plant species, held in check by insects and pathogens in their home range, become invasive in their introduced range where those insects and pathogens are lacking. Strawberry guava seems to fit the “enemy release” theory perfectly. In Hawaii, it is currently attacked by no insects or pathogens.

The first biocontrol researcher for this species, Dr. Charles Hodges, traveled to coastal Brazil in 1988 and reported that strawberry guava occurs not in dense stands but as scattered trees and rarely in small clumps. He noted that “few trees were observed that had not been attacked by at least one kind of insect,” and “often four or five types of insect damage could be identified on the same tree.” After 20 years of research to determine the best potential biocontrol agent, the scale insect Tectococcus ovatus has jumped through all the hoops but one – public opinion.

Lloyd Loope is a research scientist with the U.S. Geological Survey stationed at the Haleakala Field Station. He holds a doctorate in botany from Duke University and is an active member of the Maui Invasive Species Committee.

Originally published in the Maui News, September 14, 2008 as part of the Kia‘i Moku Column.
You can find all the articles in the Kia‘i Moku series http://www.hear.org/misc/mauinews/

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