Orchids and ants, early invaders of lava flows: Bamboo orchid, Arundina graminifolia and an unidentified ant, Formicidae sp.

 

Non-native bamboo orchids and ants are early colonists to newly formed volcanic soils in Hawai’i.

 

Native to several countries in Asia, beautiful bamboo orchids are now found on continents and islands around the globe.

In last week’s visit to Hawai’i we met one of many species of small sucking insects known as psyllids that have evolved along with their iconic native host plant, the ʻŌhiʻa tree, one of the first colonists of lava flows. This week we return to the Kilauea volcano on the big island to meet two non-native invaders to these remote islands. Recall that this chain of land masses formed as the earth’s crust passed over a volcanic hot spot beneath the Pacific Ocean over the course of some five million years. Flora and fauna extant on this archipelago are comprised of descendants of ancient colonists or more recent travelers that arrived from elsewhere with or without assistance from humans. The stark beauty of the lava flow on Kilauea’s Iki trail is punctuated not only by the indigenous ʻŌhiʻa, but also by a drop-dead gorgeous orchid known as the bamboo orchid, Arundina graminifolia. Bamboo orchids are native to tropical biomes in several Asian countries but have been introduced to countries in Central America, the Caribbean, and several Pacific islands, including Hawai’i where they readily colonize newly formed volcanic soils. Plants are not alone in their abilities to colonize new lands. Insects are also renowned for their peripatetic abilities and amongst the best of these travelers are ants, anointed by famed entomologist and sociobiologist E. O. Wilson as the “little things that run the world.” Ants created quite a stir in the media earlier this year when scientists released their findings that we share our planet with some 20,000,000,000,000,000 members of this six-legged clan. Ants are found on every continent on earth except Antarctica, which seems strange as this continent is the only one with “ant” in its name (LOL). Several islands also lack ants, but not so for the Hawaiian Islands where more than 60 species of ants have been introduced over the last few centuries with an assist from humans, as imported plants and products arrived on the islands.

The lava lake on the floor of erupting Kilauea Volcano creates new land. Among the first plants to colonize a recent lava flow is the beautiful non-native bamboo orchid. Not surprisingly, an unidentified species of ant is one pioneer to make this newly formed land its home, where it searches orchid blossoms for sustenance.

While always on the lookout for bugs and their relatives, it was no surprise to find the non-native bamboo orchid colonized by one of the many non-native ants busily exploring its blossoms, apparently in search of a plant product like nectar or perhaps honeydew-producing insects like aphids. Described as “ecosystem engineers”, ants play vital roles in global ecosystems providing services such as seed dispersal for plants, biological control of crop pests, aeration of soil, linking trophic levels of food webs, and decomposition of organic matter. However, recent invasions of pestiferous “tramp ants” to Hawai’i, including little and tropical fire ants, pose threats to humans and pets by virtue of their memorable sting. These and invasive yellow crazy ants attack and kill other arthropods, including native and non-native invertebrates like spiders, crabs, and insects, and also small vertebrates, including birds, reptiles, amphibians, and mammals. They may also defend colonies of sap-sucking insects like aphids that damage ornamental plants and crops.  A small dedicated band of scientists at the Hawai’i Ant Lab are tracking the spread of invasive ants. Their mission is to protect Hawai’i from new ant invasions, prevent the spread of established invasive ants, eradicate new infestations, and help homeowners, resource managers, and businesses to find new ways to manage the ongoing influx of these emerging pests. Don’t know if the tiny ants attending bamboo orchids are a boon or a bane to Hawai’i’s’ ecosystems, but they, along with these orchids are one of the first insect colonists to gain a foothold on new land. 

Acknowledgements

Bug of the Week thanks the ranger crew at Volcano National Park for suggesting locations to enjoy the spectacular natural beauty of the geology and biology found in the park. Enlightening discussions with Drs. Dan Gruner and Paula Shrewsbury helped shape this episode. Thr wonderful articles “The Little Things That Run the World (The Importance and Conservation of Invertebrates)” by Edward O. Wilson and “The abundance, biomass, and distribution of ants on Earth” by Patrick Schultheiss, Sabine S. Nooten, Runxi Wang, and Benoit Guénard, were consulted for content presented herein.

To learn more about invasive ants in Hawai’i, please visit this website: https://littlefireants.com/  

Destination Hawai’i, where strange insects colonize new land: Psyllid galls on ʻŌhiʻa tree, Pariaconus spp.

 

Nestled inside a leaf gall, a tiny Pariaconus nymph with wing buds will soon molt to become an adult.

 

New land formed this week with ongoing eruptions in the lava lake of Kilauea and lava flows of Mauna Loa.

As the weather cools down throughout North America, let’s head to somewhere hot, really hot, to the Mauna Loa and Kilauea volcanos on the big island of Hawai’i, where lava erupts from vents at some 2000 degrees Fahrenheit and creates some of the youngest land on Earth. The Hawaiian Islands are an archipelago, a chain of land masses formed as the earth’s crust passes over a volcanic hot spot beneath the Pacific Ocean. The northernmost islands in the string, Kaua’i and Ni'ihau, were born around 5 million years ago but the youngster of the bunch is Hawai’i, which arose from the seafloor only some half million years ago. It continues to grow with ongoing eruptions and lava flows.

In the other-worldly landscape of a recent lava flow, sacred ʻŌhiʻa trees are among the first colonists to take root.

A hike across a lava flow on the Kīlauea Iki trail provides fascinating clues to the formation of the rich floral and faunal diversity of the Hawaiian Islands. One of the first colonists to a virgin larva field is the sacred ʻŌhiʻa tree, Metrosideros polymorpha. This keystone species comprises some 80% of the native forests on the big island and provides habitat and food for many of Hawai’i’s endangered birds and insects. Scattered across the moonscape of a 1959 larva flow are young ʻŌhiʻa trees whose roots miraculously pierce the ropy lava to collect water and nutrients, which support a leafy canopy and brilliant ʻŌhiʻa blossoms. While examining these remarkable trees, we observed several with Hershey-kiss-shaped galls on the lower surface of many leaves. Galls are abnormal growths on plants created by several species of insects and mites that secrete potent chemicals into the plant’s undifferentiated tissues. These chemicals derail the normal developmental processes of the plant and create food and refuge for the insect or mite at the expense of the unwitting plant host. We met other species on gall making insects in previous episodes on oaks, tupelo, spruce, and elm.

Spectacular eruptions of Mauna Loa and Kilauea volcanos on Hawai’i transport lava from deep within the earth to the surface to form new land. One of the first plants to colonize virgin larva flows is a keystone species, the sacred ʻŌhiʻa tree. Strange Hershey-kiss-shaped leaf galls are home to one of some three dozen psyllid species that evolved on the Hawaiian Islands. Tiny sap-sucking nymphs with wing buds will soon mature and pop the top of their gall to emerge as winged adults ready to mate and colonize new ʻŌhiʻa trees. Adult psyllids utilizing ʻŌhiʻa are similar in appearance to the adult boxwood psyllid depicted here next to its shed nymphal skin.

Galls on ʻŌhiʻa are formed by a clan of sucking insects called psyllids, members of a large order of insects known as the Hemiptera - stink bugs, assassin bugs, bed bugs and their pernicious relatives like aphids, whiteflies, adelgids, scale insects, and many others. The tiny gall-makers on ʻŌhiʻa are members of a genus of psyllids named Pariaconus, a taxon with 36 named species on the Hawaiian Islands associated with Metrosideros polymorpha. Many of these psyllids are free-living and don’t form galls, while others form unique and interesting galls on stems and leaves. Why so many species of Pariaconus on but one species of plant? Well, it turns out that ʻŌhiʻa has a remarkable ability to colonize and thrive in many different soil types, zones of varying rainfall, and at many different altitudes found on the Hawaiian Islands. From the time the ancient ancestors of modern day Pariaconus arrived on these islands, which are the most isolated islands on earth, they were able to evolve and diversify in the myriad habitats occupied by Metrosideros polymorpha. These varied and unique niches spawned the great diversity of psyllids seen on the islands today. This form of diversification or radiation of species on islands was made famous by Darwin and his observations of the Galápagos finches in “On the Origin of Species by Means of Natural Selection”.  

Rapid ʻŌhiʻa Death (ROD) caused by two fungi has killed tens of thousands of trees on Hawai’i, threatening not only this culturally important tree but myriad insects, birds, and other wildlife intimately associated with this keystone species.

But all is not well for the iconic and irreplaceable ʻŌhiʻa tree and the insects and other creatures that call it home. While it seems to tolerate its psyllid guests reasonably well, it is threatened by two species of lethal fungi, Ceratocystis lukuohia and Ceratocystis huliohia, causal agents of Rapid ʻŌhiʻa Death (ROD). First identified in 2014 on the big island, by 2019 it had infected more than 175,000 acres of trees. Through activities like moving infected wood, wounding trees with contaminated tools, and walking on or moving infected soil, humans are believed to help spread these fungi. Feral animals moving beneath infected trees and small bark beetles may also spread the disease. Efforts are underway to stop the spread of ROD and save this iconic tree so intertwined with Hawaiian culture and so important to the ecology and biodiversity of these unique and irreplaceable forests. 

Acknowledgements

We thank Dan Gruner for stimulating discussions about the ecology of Hawaiian flora and fauna and Paula Shrewsbury for images used in this episode. The great article “Making the most of your host: the Metrosideros-feeding psyllids (Hemiptera, Psylloidea) of the Hawaiian Islands” by Diana M. Percy was consulted for this episode.

To learn more about ROD and its management, please visit the following websites:

https://cms.ctahr.hawaii.edu/rod/THE-DISEASE

https://dlnr.hawaii.gov/hisc/info/species/rapid-ohia-death/