New insects released to help suppress ivy gourd

About 50 gall-forming weevils were released yesterday in Kagman to augment the efforts of leaf-mining weevils in suppressing the noxious ivy gourd’s population on Saipan.

Entomologist Dr. Rangaswamy N. Muniappan, Department of Lands and Natural Resources Secretary Richard Seman and Division of Agriculture director Donald Flores released the weevils as part of bio-control efforts to rid the island of the invasive plant. The ivy gourd now covers about 35 percent of plant life on Saipan, and small infestations have also been reported on Tinian and Rota.

Muniappan said the gall-forming weevils, acythopeus burkhartorum, lay their eggs on the petioles of ivy gourd leaves. The larvae then penetrate the petioles, causing it to swell as they develop to pupa stage, after which the petioles fall from the stem. Upon reaching adulthood, the weevils also feed on the ivy gourd.

“That’s how this weevil damages the ivy gourd,” he said.

Muniappan disclosed that 60 weevils were brought in from Hawaii, 10 of which were kept at the Division of Agriculture facility for culturing. Once the weevils at the division increase in number, more can be released in other areas.

Muniappan said that after about six months, the weevils released yesterday could be harvested and transferred to another location.

“With the 50 that we released today, it would take about six months before it will multiply to about 500. We can find some and release them somewhere else,” he said.

The weevils have a life span of six to nine months.

The project is being funded by the U.S. Department of Agriculture.

Muniappan indicated the possibility of adding another bio-control agent, the stemboring moth, in about a year.

“We’re looking for a combination of the agents,” he said “So we are brining three agents to suppress this weed, so we will see each one increase the effectiveness of suppressing this plant.”

He said efforts are primarily focused on suppressing the ivy gourd and that eradication of the ivy gourd is “not possible.”

The entomologist indicated that the leaf-mining weevils released in 2003 are the most effective in suppressing the ivy gourd.

“You see the defoliation [of the leaves],” he said. ‘It kind of dried up.”

The project is being funded by the U.S. Department of Agriculture.

He said, however, that the impact of the weevils won’t be seen until the insect’s population is great enough.

“It takes time, we put in 50 and it has to multiply,” he said. “By the time you see any impact on the plant, it has to multiply to closer to about half a million. The plant also keeps growing, but eventually they [weevils] have to catch up, and when the population of this weevils increase…that’s when you will see the impact.”

He said the impact of the first weevils introduced in 2003 was good but could not be determined in some areas because the ivy gourds were cleared by humans.

He also indicated that the typhoons experienced last year had little effect on the weevils that were earlier released. “It only kind of moved the weevil from one area to another.”

Muniappan cautioned against the use of herbicides to suppress the ivy, citing that it would affect the plants beneath the gourd.

An African vine of the melon family Cucurbitacae, the ivy gourd was allegedly smuggled to Saipan in the 1990s. The invasive vine destroys plant life and any other living matter underneath it.