From pets to pests: The case of the rice planthoppers

Published on Thursday, 22 August 2013

Published by on Thursday, 22 August 2013

Planthoppers feeding on a rice stalk. Photo credit: IRRI
Planthoppers feeding on a rice stalk. Photo credit: IRRI

Written by Lourdes Adriano, Agriculture, Rural Development, and Food Security CoP

In my childhood years, we considered planthoppers as pets. My brothers would catch, feed and train them for hopping races with other kids. Little did I know that these seemingly harmless insects can become crop destroying pests.

Large swarms of brown planthoppers (BPH) have surged in recent years, devastating rice fields across East and Southeast Asia. Since 2005, the People's Republic of China (PRC) has been losing an average of 1 million tons of paddy rice annually because of these outbreaks. In early 2012, the PRC’s southwestern province, alone, lost about 10 million tons of rice. 

Similarly, the rice bowls of Thailand and Vietnam have suffered huge losses from these tiny winged predators. At the peak of the food price crisis in 2008, Viet Nam lost 1 million tons of rice, resulting in a government freeze on rice exports which contributed to a surge in rice prices. In Thailand, for 10 consecutive growing seasons from 2008 to 2012, persistent BPH outbreaks were like a biblical pestilence, causing millions of dollars worth of crop losses. The planthoppers have crossed national boundaries to Myanmar, the South Asian economies of India and Bangladesh, and other parts of Asia. 

Like a blizzard: Planthoppers swarm near rice fields in People's Republic of China (PRC).

In all these countries the major cause of the outbreaks has been the excessive use of insecticides. Scientific studies show that BPH infestations occur 10 times more on sprayed fields. Ironically, these insecticides should have controlled and killed these pests. So, why aren’t they doing their job?

Planthoppers live and breed only in rice ecosystems. They thrive on rice plants at very low numbers of about 5 per plant. If they increase in number, natural predators regulate their population. However, too much spraying of insecticides at the early stages of planting only induces the population to increase exponentially. Too much insecticide spray  kills the natural pest controls in the rice ecosystem during the vulnerable growing stage of the rice plant. These induce the BPH which have also become resistant to the chemicals to freely multiply and attack the rice plant. 

Farmers tend to use more rather than less of the insecticides, which are readily available in village stores like food items. To make matters worse, they do not get proper technical guidance from extension workers or from the insecticide companies who sell the chemicals like fast-moving consumer goods. Some insecticides which are banned in developed economies are still sold in rural Southeast Asia. 

Dry, brown patch shows planthopper infestation. Photo credit: IRRI

But with technical assistance from ADB, the International Rice Research Institute (IRRI) is working on a two-pronged, natural method of controlling planthoppers. The long-term approach involves developing a rice seed variety that is resistant to BPH. In the shorter-term, another action is being taken to control the insect which is both ecology friendly and improving the landscape. With the help of IRRI scientists, farmers in Southeast Asia, especially women farmers, are being taught to plant brightly colored flowers on the sides of paddy fields and to reduce their use of insecticides. The flowers serve to attract rice plant-friendly insects like bees and other organisms, which are natural predators of planthoppers (like bees) , and so help control the growth rate of the BPH population. 

In Viet Nam, women farmers have readily adopted this ecofriendly practice. Insecticide use in project areas has dropped by 22% while spending for insect control has slid from $27 to $16 per cropping season. These farmer households are now saving as much as $50–$100 per cropping season. Not only do their paddy fields look picturesque, but they are also helping restore balance in the rice ecosystem. And, maybe, for a child somewhere in those fields, the days when planthoppers served as pets rather than pests will soon return.   

Author's note: The main reference of this blog is K. Heong et al. 2013. Addressing Planthopper Threats to Asian Rice Farming and Food Security: Fixing Insecticide Misuse. ADB Sustainable Development Working Paper Series.  No. 27. Manila: Asian Development Bank.