Wasps threaten to wipe out RP’s beautiful dapdap trees

Los Baños, Laguna — A newly identified parasitic wasp threatens to devastate the country’s beautiful dapdap trees.

Horacio San Valentin, an entomologist of the Department of Environment and Natural Resources-Ecosystems Research and Development Bureau (DENR-ERDB) based here, named the pest Erythrina gall wasp (EGW).

Dapdap (scientific name: Erythrina variegata) is an indigenous species widely distributed in the Philippines. It can grow up to 15 meters, with its radiant red flowers a sight to behold from January to May.

Today, however, only a few dapdap trees can be seen around because low regions, especially seashores (the species’ habitat), have been gobbled by human settlements in view of the country’s burgeoning population.

Early this year, the ERDB, headed by director Celso Diaz, reported that some dapdap trees in Laguna, Quezon and Metro Manila were observed to have gall-damaged leaves and stems. By summer, old and mature trees were defoliated prematurely, leading to the death of many of the trees.

"Our inspection of the dead dapdap trees inside the Ninoy Aquino Parks and Wildlife Center (last) July revealed that the trees died of severe gall (sore) wasp infestation," San Valentin said.

"The dead dapdap trees are still standing in the park, posing hazards to visitors and properties," he said.

The wasp attacking dapdap trees is very small, measuring only one to 1.5 millimeters.

It inserts its eggs into young leaves and stem tissues. Its larvae, which develop within plant tissues, induce the formation of galls in leaflets and petioles.

As infestation progresses, leaves curl and appear deformed. When feeding is complete, the larvae pupate within the leaves and stem tissues. After pupation within the galls, wasps cut an exit from the galls in the leaves and stems.

Severe infestations can cause defoliation and death of dapdap trees.

San Valentin became doubly alarmed when he read about scientific reports of similar cases in Singapore, Taiwan, and Hawaii, where Erythrina trees have been grown for decades.

The reports also identified the wasp as Erythrina gall wasp, which was originally described from Singapore. It has since been found in the Philippines, Hong Kong, China, Taiwan, India and Hawaii.

Accordingly, it seems to be moving around, severely attacking several species of Erythrina. The exact origin remains unknown.

"We hope to do something soon because the wasp might be another invasive species similar to the ipil-ipil psyllid, which wiped out the ipil-ipil throughout the Philippines in the 1980s," San Valentin said.

The ERDB said there are ways of eliminating the insect pest.

It, however, cautioned people on the use of synthetic insecticides, which may be effective agents but have hazardous effects on people.

More effective and safer control measures that can be combined with chemical treatments include thinning, intercropping, and multiple cropping of non-hosts.

"But the most effective means and a long-term solution is classical biological control using parasitoids from the gall wasp’s native region. But we are still conducting investigations to identify the wasp’s origin," San Valentin said.

The extent of damage to dapdap trees in the Philippines also needs to be determined.

San Valentin said, "Limited financial allocations in our research and development work hinder us from traveling throughout the country to find out the condition of dapdap trees."

He added: "Hence, we hope that concerned individuals or groups can report to us if dapdap trees in their localities are under the same infestations."

Information can be relayed to the ERDB at telephone number (049) 536-2269/2220, or e-mail addresses [email protected], [email protected] or [email protected].

"With your reports, we can promptly save every dapdap tree that is not yet heavily infested and prevent further infestation," San Valentin said.