To Fight Invading Beetle, Experts Recruit a Wasp

Traing District, Takeo Province – Surrounded by leafy walls of coconut palm trees, most with brittle dropping spears, Wilco Leibregts knows the silent enemy he’s been hunting across Southeast Asia and the Western Pacific is very, very close.

With the blade from his pocketknife, he slowly cuts opens a new palm leaf like a fan.  And sure enough, hidden inside the spear, carving scars on the epidermis of a developing leaf, is the 10mm long insect he knew he’d find: an invasive species of beetle that threatens the survival of the coconut tree as it sweeps across borders to gobble up new territory.

“They’re extremely efficient pests,” said Leibregts, a consultant for the UN Food and Agriculture Organization. “And coconut palms are its favorite food,” he said as he sliced open a squirming larval sack of the coconut beetle in a Traing district villager’s backyard grove.

The small brown and black beetle, which has caused massive losses to coconut palms from Vietnam to the Maldives, has infected more than 8 million of the estimated 12.8 million coconut trees in Cambodia since the invasive insect species arrived here from Vietnam in 1999.

To counter the infestation, the FAO has launched a project in Cambodia and other affected countries aimed at achieving long-term control of the rapidly spreading bug with the help of one of its natural enemies: A tiny parasitic wasp native to Indonesia and Papua New Guinea.

Here’s how it works: The wasp, about a millimeter long, bores into the larvae of the beetle and then lays its eggs. After killing the developing beetle in its larval sack, an average of about 50 new wasps emerge from the dried-out sack and fly off to other coconut palms to snuff out more beetle larvae.

“Biological control,” as the operation is known is the newest weapon in the war on botanical and insect invaders. To contain the spread of a foreign pest—reproducing without the predators and parasites that keep them in check in their native habitats—scientists choose a natural enemy from the area where the invader evolved to attack it in its newly-claimed territory.

“Without its natural enemies, there’s nothing to prevent an invasive species from reaching outbreak status,” said Leibregts, who led a team of local agriculture officials to let loose parasite wasps across Takeo province last week.

“By releasing a ‘host-specific’ enemy—which means that it doesn’t feed on anything else—you can bring it down to a manageable level,” he said.

Leibregts and FAO plant production officer Keith Chapman maintained that the wasp parasite does not attack other insects or plants, and that a one-time release of the parasite is all that’s required to bring about control of the beetle.

In Vietnam, the FAO said the wasp has rescued that nation’s coconut industry, which had suffered a $40-million loss in the coconut industry and 5-percent loss of coconut trees per year due to the voracious beetle. Current losses in Cambodia, where coconut is a common backyard crop, are estimated at more than 25 million coconuts per year.

But establishing the biological control takes time, anywhere between 8 to 11 months, according to scientists. However, once the wasps are established in an area, the chances of re-infestation of the coconut beetle, which is believed to have been imported into Cambodia with ornamental palm trees, is nil.

“Once it works, you don’t have to worry about it anymore,” said Leibregts, as he tapped the tiny wasps out of a plastic tube and onto a coconut palm spear. “It’s not like with pesticides, which you have to apply over and over.”

When the coconut beetle was first discovered in Cambodia, officials said government authorities responded with the application of insecticides to the crown and stem of infested coconut trees. But the pest continued to spread with the fervor and resilience of an invading army.

“The application of insecticides can only serve as a temporary control measure,” said Tran Tan Viet, a biocontrol specialist at Nong Lam University in Vietnam, where the parasite wasps have been mass-reared in boxes in a FAO-project laboratory. “Biological control is the most effective method, given the cost and benefit ratio,” he said.

Across the globe, however, there are some notorious examples of biocontrol having gone wrong. The cane toad, for instance, which is native to South America, continues to hop amok in Australia more than seven decades after it was introduced to control greyback beetles killing the sugar cane crop.

But past catastrophes involving predators should not cause worry about biological controls such as the parasite wasp, Leibregts said.

“Nowadays there’s a lot more research and more understanding of the way these things work,” he said. “There are very stringent control measures to make sure that the right host-specific enemy is introduced.”

Along with the release of the wasps in Takeo and Kampot provinces, where there are thousands of severely damaged trees, officials have launched a village awareness program to let  Cambodian farmers know about the coconut beetle damaging their trees and the way the parasite can prevent this.

Chapman, who is based in the Bangkok FAO bureau, said a key message to rural communities is not to transport palms from one area to another as this is the quickest way to help the coconut beetle spread.

“These beetles are terribly efficient, and it’s important that they’re not given a leg up by people transporting the bloody things around,” he said. “That’s when the trouble starts.”




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