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Entomologists look to Hawaii controls

By Haidee V. Eugenio SAIPAN, CNMI (Saipan Tribune, April 26, 2010) - Erythrina Gall, a wasp, has been tagged as the culprit behind the decline in the number of coral or gao gao trees, while a certain moth has become a serious pest of fruits in the Commonwealth of the Northern Mariana Islands (CNMI), according to a local entomologist.

Dr. Marisol Quintanilla, an entomologist in the Northern Marianas College's Cooperative Research Extension and Education Services, says that controlling these insects by chemical can be costly.

"We have noticed the decline of gao gao trees, and we agree that this is a very unfortunate event," Quintanilla told Rep. Stanley Torres (Ind-Saipan), who had raised concerns about a number of coral trees dying on Saipan.

Torres thought the death of coral or gao gao trees may have been caused by the scarlet gourd weevil and the scarlet gourd vine borer, both biological controls imported for controlling the pest vine scarlet gourd.

Saipan has been having problems with the invasive vine scarlet gourd. Since 2003, the government has used parasitic insects to feed on and destroy scarlet gourds.

Torres said while he agrees with the Northern Marianas College-Cooperative Research, Extension and Education Service (NMC-CREES) assessment that the scarlet gourd situation on Saipan is improving, he has also witnessed damage done to a medicinal tree on Saipan called the coral or gao gao tree.

But Quintanilla said these biological controls do not successfully feed or reproduce on other hosts beside scarlet gourd.

She said the insect that is attacking the gao gao or Erythrina trees is the Erythrina Gall wasp. This insect was first described in Taiwan, and is attacking gao gao trees in Hawaii.

Quintanilla described the insect as "very small, almost as small as dust, and can travel inside a person's luggage, inside airplanes and possibly in plant material." She said Erythrina Gall wasp entered the CNMI accidentally.

She said Hawaii has released biocontrol agents to control the Erythrina Gall wasp, and the CNMI could potentially do the same.

But she said the gao gao tree is also a host for the fruit piercing moth, which is a "serious pest of fruits in the CNMI."

This moth attacks banana, citrus, guava, mango, tomato and others.

"If we introduce biocontrol to save the tree, we would also be saving this serious pest. Another solution could be to use chemical control, which would control both the Erythrina Gall wasp and the fruit piercing moth. This can be used only on selected trees because of the expense involved. Chemicals are expensive and if injection or application would have to be done to every single tree, the cost might be prohibitive," Quintanilla told Torres.

Torres said he had to cut down 13 coral trees on his property on Capital Hill before they fall on his head.

"I believe this situation needs your immediate attention, and please advise me of your current opinion and findings in this matter as soon a possible," he said. Quintanilla responded to his April 19 letter, and agreed to inspect the trees on Torres' property.

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