THAILAND: Insect influx threatens rice production

Aug 25th, 2010 | Category: Environment

The brown planthopper is a major pest of rice in Asia/Photo: Courtesy of IRRI

Experts warn that a significant increase in the numbers of brown hoppers, a rice pest, in central Thailand, threatens production.

“The current situation is not good,” KL Heong, an insect ecologist from the International Rice Research Institute (IRRI) told IRIN in Bangkok. “Looking at the number of hoppers caught in light traps over the last two months, it’s clear that a massive immigration has occurred.”

Light traps are used to measure population levels of migrating hoppers within a 9.1-15m radius. On an average night, a light trap will catch 10-20 hoppers. During migration peaks (twice a year), this can rise to about 2,000 per night.

Heong recently spent three days visiting fields, farmers and agricultural experts in Suphan Buri, Chainat and Ang Thong provinces where he saw traps with up to 40,000 hoppers and “nymphs hatching all over the place”. Anything above 10,000 is alarming, Heong says.

“This will peak around December. I expect 30 percent losses in most rice fields,” Heong warned.

The hoppers, known scientifically as Nilaparvata lugens, remove plant sap with their mouths, causing the tillers – any of the extra stems or culms in a rice plant that arise from its base – to dry out and turn brown, a condition called “hopper burn”.

It also transmits two viruses, “ragged stunt” and “grassy stunt”, both of which render the rice crop infertile.

According to the Ministry of Agriculture, from November 2008 to May 2009 (the dry season) Thailand lost 1.1 million MT of rice due to hopper outbreaks, costing an estimated US$275 million. Thailand, the world’s top exporter of rice, produced more than 27 million MT in 2009, says the UN Food and Agriculture Organization.

With similar insect population numbers this summer, the Ministry of Agriculture warns of at least the same losses this year.

“Our estimates on production will have to be reduced,” Wantana Sriratanasak, an entomologist with Thailand’s Department of Agriculture, said.

Pesticide use

According to Heong, extensive pesticide use by farmers is the primary reason for the infestations. Pesticides have a limited effect on plant hoppers but kill off their natural predators, including several species of spiders. The insects have a high migratory ability and fast reproduction rates, exacerbating the threat.

Thai authorities are looking for regional and practical solutions to manage and prevent future outbreaks.

“We’ve been collaborating on a project for two years with China and Vietnam. Both countries still have a serious problem with outbreaks,” Sriratanasak said. The focus will be on improving biodiversity while simultaneously reducing pesticide use.

Vietnam lost four million MT in 2007 because of outbreaks, while China regularly loses a million hectares a year.

The Rice Department is working to encourage local farmers to reduce spraying, Kukint Soitong, a senior expert in the department confirmed.

“We have to change farmers’ chemical use,” he said, “but it’s not easy.”

IRIN News
cm/ds/mw

[This report does not necessarily reflect the views of the United Nations]

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