Parasitic bug could save wiliwili trees
By Rod Ohira
Advertiser Staff Writer
By Rod Ohira
A state exploratory entomologist may have found a natural enemy to destroy a rapidly spreading gall wasp that is threatening to wipe out Hawai'i's native wiliwili tree population.
For two months, Mohsen Ramadan roamed Tanzania in eastern Africa in search of a natural solution to fight the Erythrina gall wasp. He ended up finding a wasp of the Eurytoma species that feeds externally on gall wasp larvae and pupae.
"I'm very excited about this parasitoid," Ramadan said, "because it attacks 95 percent of the gall wasps in Tanzania."
Ramadan sent the parasitoid — which means it kills its host — to Hawai'i, where state agriculture biocontrol officials have been conducting tests on its effect and to ensure it doesn't pose threats to anything other than the gall wasp.
State Department of Agriculture Plant Pest Control Branch biocontrol section officials are encouraged by what they've seen in lab tests of the Eurytoma wasp, which doesn't have a name. The parasitoid produced its first generation in their lab last week, at the expense of gall wasps.
"If this proves to be specific," Ramadan said, meaning there's no threat other than to gall wasps, "it will save the wiliwili."
It could take up to a year for the testing process to be completed and to obtain approval from state and federal agencies for permits to release the parasitoid, Ramadan said.
State biocontrol section chief Kenneth Teramoto said the tests are "very promising."
"We know it works in the field but we still have to do the non-target (testing)," he said.
The parasitoid and gall wasp, each less than one-quarter the size of a mosquito, do not pose a threat to humans or animals, but the gall wasp could destroy the native wiliwili tree population.
The Erythrina gall wasp "is the fastest spreading devastating insect we've encountered, at least in my career," said Teramoto, who has been with the Plant Pest Control Branch since 1973.
The gall wasp is a new species, not only to Hawai'i, where it was first detected in April 2005, but worldwide. Teramoto said its presence was first documented three years ago in Taiwan, and in Singapore, Mauritius and Reunion in 2004.
So how did it get to Hawai'i?
"That's the million-dollar question," Teramoto said. "Speculation is it came from Taiwan because Taiwan has a developing ornamental-plant industry."
The Agriculture Department's 2005 annual report says information about gall wasps is limited to description, host plants, damage and current distribution. Its origin or native range is unknown.
The insect's name comes from the ulcer-like distortions called galls on leaves, stems and shoots caused by the plant's reaction to larvae developing within its tissue. In Hawai'i, the wasp is ravaging the native wiliwili, especially in Maui's dryland forest, and the "tropic coral," also known as "tall erythrina."
Plants can survive the galls, but the attacks on the shoots are stepping up a sense of urgency. "It stunts the growth," Teramoto said. "It puts so much pressure during dry times that the trees cannot withstand it."
Attempts at pruning on Maui have failed, so wiliwili seeds are now being collected in an effort to save the tree from extinction.
Ramadan, a 54-year-old native of Egypt who has been working for the state agriculture department since 1997, studied the situation and recommended searching for a natural enemy in Tanzania because the country, which borders the Indian Ocean, has more than 15 Erythrina species.
"The whole idea was to find the native region of gall wasps and go there to look for a natural enemy," said Ramadan, who earned his master's and doctorate at the University of Hawai'i.
Ramadan's search began with an eight-hour bus ride from Morogoro to Iringa. He had to rent cars and hire guides, who would request armed guards at different village stops. His work in Tanzania, where dangers range from contracting cholera to meeting with bandits, took him to Mwanza, on the shores of Lake Victoria, and Arusha, near Serengeti National Park, among other places.
Finding Erythrina was difficult enough but there were other challenges.
"Every village police will stop you and ask if you have permits or about what you're collecting," Ramadan said. "At the end, they'll ask you for soda money. Two dollars was usually enough for them."
The mission was rewarding, Ramadan said. "My first week, I found three different parasitic wasps," he said. "I was looking for galls but saw only 10 to 20 leaves had galls so I knew something was limiting their numbers."
His first trip was during the dry season, so Ramadan plans to return to Tanzania to look for parasitoids during a different climate period.
Ramadan is no stranger to exploratory missions.
In 1998, he traveled to Guatemala in search of a natural enemy for miconia. "He was unsuccessful," Teramoto said regarding the miconia solution, "but he sent back a parasitoid that is used to control the citrus black fly."
The following year, Ramadan went to South Africa and Madagascar and found two moths that are natural enemies of fire weeds.
Other trips were to Egypt, Thailand and Malaysia, and back to Madagascar and South Africa in search of answers to fountaingrass and melon fly problems here.
Reach Rod Ohira at email@example.com.