By K.L. Heong
International Rice Research Institute
White-backed planthopper, Photo credit: S. Villareal (IRRI)
Pest storm in China, Photo credit: Z. Lu (ZAAS)
China loses about a million tons of paddy caused by planthopper outbreaks annually. This is despite the huge amounts of pesticides being used by farmers. On average, Chinese rice farmers spray at least 3 times more than farmers in the Philippines. In 2005, planthopper outbreaks were very extensive in 5 provinces and some estimates show that China lost 2.8 million tons of paddy. Some researchers attributed these extraordinary outbreaks to elevated summer temperatures. Is this an expected effect of climate change? Why does China experience such high intensive outbreaks of planthoppers, which most entomologists classify as “secondary outbreaks? In the 1970s, Californian entomologists, led by Robert van den Bosch, described how agriculturalists create an insecticidal treadmill because of the new pesticides that were used extensively. Three phenomena were observed: 1) target pest resurgence, 2) secondary pest outbreaks and 3) pesticide resistance. All these are related to the increasing “pesticide addiction”. Today we see the same three phenomena occurring in highly intensive rice production systems of China, Vietnam and India.
About 35 years ago, rice intensification programs in Asia, particularly Indonesia and the Philippines, had similar experiences with rice planthoppers. Through the introduction of IPM, insecticide reduction campaigns, farmer training and policy changes to reduce pesticide use, the planthopper problem had become insignificant. Subsequently, entomological research and planthoppers in particular, began to receive lesser attention In 2005, the planthopper problem was not only serious in China, but in Japan, Vietnam, Korea and Malaysia as well and it is a wake-up call. We seem to have neglected the basic ecological principles of IPM. The key question we now need to address is “Will planthoppers become a threat to the sustainability of intensive rice systems?”. This question was addressed in a paper “Are planthopper problems due to breakdown in ecosystem services?”
The International Rice Research Institute (IRRI) initiated an international scientific discussion by organizing an International Conference, which brought together 88 scientists, agricultural directors and pesticide company representatives from Australia, Bangladesh, Cambodia, China, FAO, India, Indonesia, Japan, Korea, Laos, Malaysia, Philippines, Singapore, Taiwan, Thailand, USA and Vietnam to develop new approaches, new techniques and management tools. Report of the Conference is available.
The ecological engineering or eco-engineering approach is a new direction in sustainable pest management introduced by Professor Geoff Gurr in the Conference. The principles and examples are discussed in his book “Ecological Engineering for Pest Management” published by CABI publishing. The eco engineering approach provides a framework to strengthen essential pest management ecosystem services that will improve crop health, thus preventing secondary pest outbreaks, like planthoppers. The utilization of these principles are now being explored in Guilin, China by the Ministry of Agriculture and in Jin Hua by the Zhejiang Academy of Agricultural Sciences (ZAAS).
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The recent plant hopper outbreaks are the result of an initial period of complacency when newer insecticide molecules seem to provide miracle pest control. Natural enemies of hoppers abound in nature. Yet the question most researchers in this field face is “Can such biodiversity really be the answer to pest management?” In rice it is a well establishes fact that conservation biocontrol works better. If some sound principles can be worked out taking into consideration regional differences in biodiversity , it would be the best way. The eco-engineering approach is a commendable step in this direction
I learned that IPM approach advised farmers to do not spray insecticide during the first 40 days after sowing or transplanting because the rice plant can compensate for insect damage during this time. However, I do not hear about the role of natural enemies in the field at this time. Do you have any reference for this aspect (?) because I would like to conduct a small research on the composition of pest and natural enemies at this duration on HYR varieties in Mekong Delta of Vietnam for halping me to explain to the farmers.
With my appreciation for posting the topic.
Dr Huynh
A lot of such research have been done. Most of them are summarized in the paper Heong and Schoenly (1998). Impact of insecticides on herbivore-natural enemy communities in tropical rice ecosystems. Pp 381-403 ( P. T. Haskell and P. McEwen Eds.) Ecotoxicology: Pesticides and Beneficial Organisms. Chapman and Hall, London.
This is a disturbing experience. Africa has to learn from this and define ecosystem services and how natural control can be sustainably used. Otherwise, such occurrence is not exclusive to Asia.
Africa has the same two planthopper genera, Nilaparvata and Sogatella as in Asia. We know very little about these species. From the ecological behavior of their sister species in Asia, it seems likely that they will respond in the same manner. Rice is being introduced into Africa at an alarming speed and most efforts focus on yields and production. If we dont learn from lessons of the past, i think we are bound to repeat the same mistakes. I think it is important that entomologists in Africa voice out their concerns to research and development agencies, so that some attention is paid to these impending problems.
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