Understanding Invertebrate Diversity in Hawai`i is Still a Work in Progress

Hawai`i’s invertebrate species may not be as celebrated as its birds or flowers, but when it comes to numbers, they take the prize in a walk. Although naturalists have been studying the islands’ “inverts” for two centuries, what’s not known about them could fill volumes.

Or, as entomologist Dan Polhemus put the case with respect to Hawai`i’s true bugs (Heteroptera), “I don’t want to sound like Donald Rumsfeld, but we have the known knowns and the known unknowns.”

Polhemus, who heads ups the Department of Land and Natural Resources’ Division of Aquatic Resources, was referring to the fact that the rate of discovery of new species of invertebrates is outstripping the rate at which these species are formally described. For many groups of invertebrates, he said, the numbers of species for which formal descriptions exist “represent a significant underestimate of the true species richness” found in the islands.

“Over the last 15 years, 156 new species of Heteroptera have been described,” he told the Hawai`i Conservation Conference held last July in Honolulu. “At this rate, it will take 20 years to deal with the known, undescribed species.”

For the Heteroptera, some 200 species, amounting to 35 percent of the number of described species, await description. What’s more, Polhemus said, “new species continue to be discovered on a regular basis,” although the rate of discovery may be expected to diminish. “Similar issues exist in all the other major Hawaiian insect orders,” Polhemus said, giving Hawai`i a “hidden biodiversity” that is not reflected in the scientific literature. “Despite serious ecological perturbations,” Polhemus concluded, “the Hawaiian Heteroptera biota retains robust faunal integrity, and is not yet in an acute state of retreat or collapse.”

As if to underscore Polhemus’ point, Curtis Ewing from the University of California at Berkeley, noted that while some 140 species of Hawaiian sap beetle have been formally described, more than 50 still await description. All of them can be traced back to a single colonizer that arrived to the archipelago nine and a half million years ago, before Kaua`i had emerged, he said.

Unlike Polhemus and his bugs, Ewing was not upbeat about the survival of these beetles, all of which are closely associated with native plants and many of which have become nearly flightless, limiting their ability to evade predators.

“A group of six closely related species has not been collected since the 1930s,” he said. All of them occupied microhabitats associated with koa, which have been invaded by non-native isopods (such as sowbugs). In addition, he warned, if the fungi on which the sap beetles feed disappear, as could happen with large-scale disturbances, the survival of the beetles themselves – occupants of the islands for millennia – could vanish.

The annual arrival of shipments of Christmas trees to the islands is an eagerly awaited event for thousands of Hawai`i families. Yet the containers bringing trees from plantations in the Pacific Northwest can also harbor unwelcome hitchhikers, especially yellowjacket wasps.

According to David Foote with the USGS Pacific Island Ecosystems Research Center in Volcano, the yellowjackets were first spotted in 1919, on Kaua`i. By 1936, they were found on O`ahu. Yet their range in the islands didn’t really expand much until the 1970s, coinciding with the start of large shipments of Christmas trees. Now the Western yellowjacket, Vespula pensylvanica, is found throughout the islands.

The wasps prey on native insects, he said, and although their impacts are not well documented, they could reduce both the abundance and diversity of native insect species. The challenge for quarantine inspectors in Hawai`i now is to prevent new introductions of Western yellowjacket queens and also keep out other species of wasps now found on the continental United States. Even though the Western yellowjacket is already here, the arrival of additional queens could mean the introduction of new genetic material to the islands, which could increase the vigor of the strain already established here, according to Robert Hollingsworth of the U.S. Department of Agriculture’s Pacific Basin Agricultural Research Center in Hilo.

Hollingsworth elaborated on the nature of the problem in his presentation at the conference. From 1993 to 2006, the number of containers of Christmas trees shipped to Hawai`i averaged 350. Most of the shipments are accompanied by phytosanitary certificates, which indicate that the trees were shaken, to remove insects, before they were packed for shipment. On arrival in Honolulu, the certified shipments are given a cursory inspection, while those without certificates are inspected more thoroughly.

But the system is not foolproof: Hollingsworth noted that the Hawai`i Department of Agriculture intercepted 271 species of arthropods on Christmas trees between 1993 and 2006.

To investigate potentially more effective quarantine treatments, Hollingsworth and Gary Chastagner of Washington State University first determined the adequacy of current methods used to remove insects, particularly yellowjackets, from the trees before they’re shipped out.

Since 1989, both Washington and Oregon require the trees to be shaken as a condition of obtaining phytosanitary certificates. If the shaking is done manually, just 10 percent of the trees have to be shaken, and if no live yellowjacket queens fall out, the entire shipment can be sealed up and sent to Hawai`i. If live queens do turn up in the trees, every tree in the shipment has to be shaken. If the shaking is done mechanically, every tree in the shipment has to be shaken. Not surprisingly, Hollingsworth said, “shipments where 100 percent of the trees were treated had a lower percentage of infestation.”

“But,” he added, “there is evidence that even mechanical shaking does not remove all the queens that might be hibernating in Christmas trees.” In 2001, inspectors found six infested containers and recovered 19 yellowjacket queens, Hollingsworth said, and the majority of these queens were in containers certified as 100 percent mechanically shaken.

Hollingsworth and Chastagner tried treating Christmas trees immediately after they were loaded into shipping containers using an aerosol formulation of pyrethrum, a natural insecticide. Because the trees are so closely packed, however, some insects survived the treatment.

The following year, they sprayed the trees before they were harvested with pyrethroid insecticides to eliminate the wasps before the trees were taken from the field. This, they found, was the most effective strategy for removing or killing insects within the trees.

“Pre-harvest sprays of pyrethroid insecticides appear to represent a safe, effective, and practical method for controlling yellowjacket wasps in Christmas trees,” Hollingworth said in a brief write-up of his talk. “In combination with mechanical shaking treatments and improved inspection protocols, this control measure could be used to greatly reduce the risk that new yellowjacket species will become established in Hawai`i.”

For something so small, the red imported fire ant (Solenopsis invicta) is capable of inflicting serious damage, warned John Gutrich of Hawai`i Pacific University.

In Texas alone, it causes $1 billion in damage a year — $200 a year for every household in the state. In the United States as a whole, expenses attributed to dealing with the ant amount to $6 billion annually.

Now that the ant has spread to California, Gutrich said, the probability that Hawai`i could be the next place hit by an infestation of the ant has increased.

Gutrich, Ellen VanGelder of the University of Hawai`i, and Lloyd Loope of the USGS Pacific Island Ecosystem Research Center at Haleakala teamed up to estimate the potential economic consequences should the red imported fire ant arrive in Hawai`i. They concluded that if the ant became established, total costs per year to Hawai`i would come to more than $211 million: $48 million to agriculture and agricultural infrastructure; $18 million to other infrastructure (including electric lines); $7 million in lost tourism revenues; and $134 million in “foregone outdoor activity” (people electing not to go outdoors because of the risk of an encounter with the stinging ants). Over a 20-year period, total costs would be some $2.5 billion.

“The worst scenario is a late reaction,” Gutrich said.

On the other hand, if Hawai`i responded quickly and was able to eradicate the ant, initial costs might be high, but the long-term savings would more than offset the eradication costs, he said.

To illustrate the point, he cited the examples of New Zealand and Australia. New Zealand has successfully fought off introductions of the ant on three occasions. New Zealand aggressively responded to RIFA invasions on three separate occasions, spending $6.1 million, Gutrich said. Australia, on the other hand, allowed the ant to become established, and since 2001, it has spent more than $137 million to deal with the ants.

Even without the red imported fire ant, Hawai`i spending on invasive species falls short of the mark, according to Chris Buddenhagen of the Hawai`i Invasive Species Council. Buddenhagen attempted to determine just how much is being spent each year in Hawai`i on managing invasive species – prevention, eradication, control, research, and public outreach.

Overall, he found spending on invasive species comes to roughly $35 million a year. State and federal government agencies account for about $15 million each, going mostly for control (61 percent) and prevention (22 percent). Not included in the total was around $15 million in private spending to control agricultural pests, “and if you included household pests such as termites total spending exceeds $100 million,” he said.

What’s being spent today is three times what was spent in 1999, but is a long ways from the $50 million that was estimated in 1999 to be required to address threats from invasive species.

“Current efforts fall short of addressing key threats in the most cost-effective manner,” he said, including keeping new pests out and fencing to protect threatened native species from ungulates.

— Patricia Tummons

Volume 18, Number 3 September 2007