Featured Pest — Maui Invasive Species Committee (MISC)

What if there were no mosquitoes in Hawaiʻi?

Posted on March 18, 2016 by Lissa Strohecker

The Aedes aegypti mosquito is the primary vector of dengue worldwide. This species is not widespread in Hawaii. Photo by James Gathany,CDC.

The news is abuzz with mosquitoes these days; outbreaks of dengue fever on Hawaiʻi Island have us all a little more nervous when the high-pitched whine of a tiny pest reaches our ear. Mosquito-vectored viruses like Zika and chikungunya are on the horizon. Health officials in both South America and Hawaiʻi Island are scrambling to find ways to reduce mosquito populations and protect human health. Scientists are busy making nearly daily advances in the lab as well. All of the energy focused on removing these pests raises the question: how would the total removal of mosquitoes alter ecosystems?

There are over 3,500 species of mosquitoes in the world, of which only a few hundred bite. Mosquitoes and their larvae are food for fish, bats, birds, and dragonflies. Male mosquitoes don’t suck blood, they daintily sip nectar. In return, they help to pollinate some aquatic plants. But despite their service as prey and pollinator, many scientists think ecosystems would recover just fine if mosquitoes were gone–other insects could fill that niche, and we’d have one less vector for disease. Good news globally, but it only gets better for Hawaiʻi.

The Culex mosquito, larvae shown here, is the mosquito responsible for spreading avian malaria between introduced and native birds. Photo by James Gathany, CDC.

In Hawaiʻi, mosquitoes are food for native bats (ʻōpeʻapeʻa) and dragonflies (pinao). Would these species go hungry without this imported food source? Not in the least, explains Dennis Lapointe, an ecologist with the US Geological Survey who researches the ecological role of mosquitoes and birds in Hawaiʻi. “[Mosquitoes] are all non-native and everything that is native and endemic got along fine without them.” Some species of native damselfly larvae eat mosquito larvae, but they have other food sources.

The greatest ecological benefit would be to our native birds. Disease-spreading mosquitoes are a significant factor keeping iʻiwi,ʻ apapane, and other Hawaiian honeycreepers from flitting through the trees in your yard.

Aedes albopictus is widespread in Hawai’i and is a vector of Zika among other human diseases. Photo by James Gathany, CDC.

Mosquitoes first arrived in Hawaiʻi when sailors dumped a barrel of water containing larvae of the Culex mosquito into the wetlands that once surrounded Lahaina. The Culex mosquito became the vector that spread avian pox and malaria from non-native birds to Hawaiian forest birds, precipitating their decline. The native passerines lacked any resistance against these foreign diseases.

Today, our few remaining native forest birds are relegated to high-elevation refuges, protected by temperatures cool enough to keep mosquitos at bay. But protection could be short lived; current estimates of climate change indicate these refugia could disappear within 80-100 years.

If mosquitoes disappeared, so would the threat of avian malaria.

Currently, the fate of native birds is not foremost in our minds as human-health threats loom: the Aedes mosquitoes, which are also found in Hawaiʻi, are in the news now. A. albopictus, widespread throughout the Islands, is the primary carrier the Zika virus. A. aegypti, a mosquito found only in a few areas on Hawaiʻi Island, is the optimum carrier of dengue. Both Aedes species carry chikungunya. Both of these mosquitoes cause harm, with negligible environmental benefit.

Meanwhile, scientists are working on a tool to reduce mosquito populations without pesticides. Using genetic technology, a self-limiting gene is inserted into the DNA of male mosquitos. Reared in labs, the mosquitos are released to seek out and mate with females, but the self –limiting genes is passed along and their offspring die as

Mosquitoes breed in standing water, and removing breeding sites is one way to help reduce the density of mosquitoes. Photo by Mary Hollinger, NOAA.

larvae. The existing adults die off and are not replaced. Though years from being ready for release into the wild, scientists predict that these altered mosquitoes could be up to 99 percent effective in reducing mosquito populations, with no risk of developing resistance to pesticides. Each species of mosquito has to be targeted specifically, but Hawaiʻi has only a handful of invasive mosquitoes, all of which are non-native.

It’s something to think about: Hawaiʻi without mosquitoes, without the threat of dengue, Zika, or chikungunya. And, as an added benefit, Hawaiian forests with a few more native birds.

Until then, continue with mosquito-control efforts: dump standing water, treat bromeliads and other plants that hold water and mosquito larvae, and regularly apply repellent. These actions can help keep these blood-suckers at bay in your backyard.

Eliminate mosquito breeding sites: https://health.hawaii.gov/docd/files/2017/01/Eliminate-Mosquito-Breeding-Sites.pdf
Ecological role of mosquitoes: www.nature.com/news/2010/100721/full/466432a.html
Avian diseases in Hawaiʻi: https://mauiforestbirds.org/avian-disease/

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.

Written by Lissa Strohecker. Originally published in the Maui News on February 14th, 2016 as part of the Kia‘i Moku Column from the Maui Invasive Species Committee.

Rapid ʻŌhiʻa Death – a new threat to our watersheds

Posted on May 19, 2015 by Lissa Strohecker

This ohia tree shows one of the characteristic symptoms of Rapid ʻŌhiʻa Death – the tree looks frozen or burnt, leaves still in place. Photo by J.B. Friday
This ʻōhiʻa tree shows one of the characteristic symptoms of Rapid Ohia Death – the tree looks frozen or burnt, leaves still in place. Photo by J.B. Friday

Five years ago, people living in the Puna district on Hawaiʻi Island started seeing native ʻōhiʻatrees in their yards dying. First, the leaves on a single limb or the whole tree would start to yellow and brown. Within days or weeks, the tree would be dead. “Trees look burnt or frozen,” explains Dr. Flint Hughes, a research ecologist with the USDA-Forest Service. He’s one of several scientists investigating the cause of Rapid ʻŌhiʻa Death, an apt description for a disease causing ʻōhiʻa to die so fast they don’t have time to drop their leaves.

Symptoms can appear in a single branch or the entire canopy of a tree. Pruning the affected brance will not save the tree since the Ceratocytis fungus is already established in throughout the tree. Photo by J. B. Friday

The disease spreads across landscapes nearly as fast. In 2012, it had killed ʻōhiʻa across about 1000 hectares (nearly 2500 acres). By last summer, it covered 6000 hectares. Healthy trees, young trees, old trees–it doesn’t matter—once symptoms appear, the tree will be dead within weeks.

A disease this virulent is potentially catastrophic for native species and watersheds. ʻōhiʻa are a keystone species for a Hawaiian rainforest. Like the uppermost stone in an arch, ʻōhiʻa is critical to the structure and function of the forest, both as refuge for native birds and other species, and as an effective way to transform what falls as rain into what comes out of the tap.

Last year, Hughes and his colleagues began to research what was happening. They knew it was a new phenomenon and not related to any previously known problems in ʻōhiʻa, such as ʻōhiʻa dieback or ʻōhiʻa rust. Within six months they had isolated the pathogen causing Rapid ʻŌhiʻa Death. The disease is caused by a fungus, Ceratocytis fimbriata. It gets into the sapwood of ʻōhiʻa, stopping the tree’s ability to transport water and sugars. “The fungus essentially strangles the tree,” says Hughes.

The ceratocytis fungus responsible for killing ohia accross 15,000 acres on Hawaii Island can be seen as a dark staining in the sapwood. Photo by J.B. Friday

Isolating the cause of Rapid ʻŌhiʻa Death, also called Ceratocytis wilt of ʻōhiʻa, is the first step. Ceratocytis has been present in Hawaiʻi for decades. In the Islands, it’s known only as a pathogen on sweet potato and taro, never before attacking ʻōhiʻa. In other parts of the world, Ceratocytis infects sycamore, eucalyptus, mango, coffee, cacao, citrus, poplar, fig, and rubber trees.

Researchers have yet to determine the origin of this recent outbreak—more than likely a new, more virulent strain of Ceratocytis was introduced but it is possible the existing strain jumped to ʻōhiʻa.

One of the researchers’ top priorities is determining how the disease is spreading. Other places

The Ceratocytis fungus spreads throughout the sapwood or vascular system of the ohia, eventually strangling the tree. The dark staining in this cross-section of an ohia is a symptom of infection by the Ceratocytis fungus. Photo by J.B. Friday

in the world, insects and contaminated equipment are vectors for spreading Ceratocytis, and that could be the case in Hawaiʻi. Until that’s determined, Hughes urges people not to move ʻōhiʻa—logs or seedlings. The fungus can survive in dead logs for a year or more. He suggests that it’s even possible that Ceratocytis spores may land on plants growing near ʻōhiʻa and movement of those plants may spread the disease

On Hawaiʻi Island some of the nicest stands of low-elevation ʻōhiʻa are gone, but researchers are not giving up. “One of the hopes is that we’ll see some genetic resistance in ʻōhiʻa, or there may be environmental constraints,” says Hughes. On Hawaiʻi Island, Ceratocytis has been found as high as about 1,400’ elevation in Mountain View, but that may reflect the relatively recent introduction rather than the full extent of its potential range.

Fungal spores of Ceratocytis on a dead log. The fungus can survive in dead logs for a year or more, and the disease can infect the plants for 2-3 months before symptoms appear. Help stop the spread by not moving ohia-logs or seedlings. Photo by J.B.Friday

They do know that the fungus can be present for months before any symptoms appear. During pathogenicity testing, ʻōhiʻa trees showed symptoms two or three months after inoculation. Pruning a symptomatic branch will not necessarily protect the tree as the fungus may have already spread throughout the tree and possibly to nearby trees.

Researchers have much to learn about Ceratocytis wilt on ʻōhiʻa. For now, they encourage people to clean boots and equipment after working on infested trees and caution against interisland movement of ʻōhiʻa logs and seedlings. Rapid ʻŌhiʻa Death is only known to occur on Hawaiʻi Island. If you are on Maui or elsewhere in the Islands and see symptoms: leaves quickly turning yellow or brown, dead trees looking burnt or frozen with leaves still in place, or tell-tale brown streaking on the dead wood, contact Hughes by phone, 808-854-2617, or e-mail fhughes@fs.fed.us Learn more online at http://www2.ctahr.hawaii.edu/forestry/disease/ohia_wilt.html

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.

Originally published in the Maui News, May 10th, 2015 as part of the Kia‘i Moku Column from the Maui Invasive Species Committee.

LFA – Insidious invaders that you can stop

Posted on August 7, 2014 by Lissa Strohecker

Ginger Johnson bought a hapu‘u fern late in 2013 to plant alongside others in her yard.

MISC employee Molly Wirth surveys for LFA in response to a Maui residents concern about little fire ant moving in hapuu. No LFA were found. MISC file photo

But when she heard the news in early January that inspectors found a new species of fire ant hitchhiking from the Big Island to Maui in hapu‘u , she thought of the hapu‘u she had just brought home. What if the ants had infested her yard? “I was very concerned. I went and looked at it and didn’t see anything.” Johnson left the hapu‘u in the shade of a tree, uncertain about what to do.

“I called a friend of mine who happened to be a biologist. He advised that I do the peanut butter and chopstick test.” The simple test, placing a peanut-butter smeared chopstick near material that may carry little fire ant, will attract many ants, including Wasmannia auropunctata, the little fire ant (LFA). Johnson tested but did not find any ants that resembled LFA, which are tiny (as long as a penny is thick) and uniformly light red in color. She was still concerned and called the Maui Invasive Species Committee (MISC) for further assistance.

Crews from MISC arrived, bagged the hapu‘u to contain any ants, and took it to the Hawai‘i Department of Agriculture (HDOA) where entomologists examined it for LFA. No suspect ants were found. But because the hapu‘u had been at Johnson’s house for a little while, MISC workers surveyed her property. They’ll return several times to ensure LFA weren’t introduced. This new pest is so damaging, it’s worth the extra effort to prevent it from becoming established on Maui.

Little fire ants can be hard to find when first introduced. Workers may not be foraging far from the queen, and even if several colonies are present, these miniscule insects are very hard to detect. Bait (like the peanut-butter-smeared chopstick) must be placed every two feet or closer. By the time the ants are stinging people or blinding pets, the population may have been present for months or years.

Little fire ants on the large end of a chopstick. Photo courtesy of the Hawaii Department of Agriculture.

These opportunistic ants don’t build mounds; rather they find shelter in leaf litter, under rocks, or in loose tree bark. Little fire ants are insidious invaders. They don’t announce their presence by swarming feet and legs; instead, they sting when they are trapped against skin or in clothing. Establishing nests in trees and amongst ground cover, LFA can reach densities of 20,000 workers per meter, or a whopping 155 ants in a square inch. At that level, painful encounters become unavoidable.

So: if it’s small, call. MISC will survey your property, using peanut butter to attract ants. Alternatively you can submit a sample to MISC. Expert taxonomists review all ants collected. If they suspect little fire ants, they’ll take the sample to HODA for confirmation.

Little fire ants are not known to be established on Maui, Lāna‘i or Moloka‘i; though small infestations have been detected and controlled on Maui and Lāna‘i. Resources exist to stop this pest in its tracks. An interagency team made up of the Hawai‘i Department of Agriculture, Hawai‘i Ant Lab, and Maui Invasive Species Committee will respond to any new infestation in Maui County.

Inspectors at the Kahului airport destroy any little-fire-ant-infested shipments they find, but some might slip through. No organization has the resources to survey all of the places or pathways LFA could travel. If you have brought any soil, potted plants, or vehicles from off-island in the last year, take time to test for LFA. Waiting until you are stung is too late.

“I’m tremendously careful now,” says Johnson. “Someone just told me the other day they got a magnolia tree from the Big Island. My first thought was: how well did you test it?”

To learn more about the little fire ant, including detailed instructions for how to survey, visit the Hawai‘i Ant Lab’s website at littlefireants.com. The HDOA site at hdoa.hawaii.gov/pi/main/lfainfo/ has updated information on spread. If you suspect you may have LFA, please don’t try to treat them yourself– contact MISC at 573-6472 or the Maui branch of HDOA at 872-2848. “The issue is so frightening,” says Johnson. “I’m born and raised here, so I’ve seen many things change. The only time to deal with something like this is before it’s a disaster.”

By Lissa Fox Strohecker. Originally published in the Maui News, May 11th, 2014 as part of the Kia‘i Moku Column from the Maui Invasive Species Committee.

What if there were no mosquitoes in Hawaiʻi?

Rapid ʻŌhiʻa Death – a new threat to our watersheds

LFA – Insidious invaders that you can stop

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