Writing in a blog post, Bouman, a research director for the Global Rice Science Partnership (GRiSP), equated neonicotinoid pesticides with the rise of planthopper outbreaks and a drop in the pest’s natural enemies.
Last week, the European Commission announced that it will restrict clothianidin, imidacloprid, and thiametoxam for a period of two years. The main reason for the ban is that neonicotinoid chemicals are believed to harm bees and to be a major cause of the so-called honey-bee colony collapse disorder. But the effect of neonicotinoid chemicals may reach beyond bees.
Planthopper outbreaks
Since 2004, Asia has witnessed massive outbreaks of planthoppers, causing severe damage to rice fields. Bouman wrote that in China alone, planthoppers are responsible for annual losses of around 1m tonnes of production, while countries in Southeast Asia have also been badly affected.
“Between 2009 and 2011, more than 3m hectares in Thailand were infested, causing losses in excess of 1.1m tonnes of paddy rice, with an export potential of US$275m,” Bouman wrote.
“Planthopper outbreaks are primarily caused by a breakdown in ecosystem resilience or biological control functions. In a healthy rice landscape, invading planthoppers are controlled by natural enemies, such as spiders, aquatic bugs, predatory bugs, and parasitoid wasps.
“When such predators and parasitoids are absent, invading planthoppers have unconstrained exponential growth, which results in outbreaks. The principal cause of a predator and parasitoid decline is the overuse and misuse of insecticides that don’t target only planthoppers but that are also toxic to parasitoids and spiders.”
Bouman said that like European farmers, their Asian rice counterparts are also known to use neonicotinoid insecticides, although “urgent investigation” is required to learn if such chemicals affect the predators and parasitoids of planthoppers.
In an effort to control planthoppers, some Asian scientists and governments have proposed a ban on—or at least the control of—broad-spectrum insecticides like cypermethrin and abamectin.
Could things get worse?
“But, what if those measures only stimulate the use of alternatives such as neonicotinoid insecticides?” asked Bouman. “Does that only make things worse?”
The rice researcher is an advocate of using enhanced biological control functions—or ecosystem resilience—to combat insect pests, with an integrated pest managment approach used to teach farmers how to distinguish what he calls “good bugs”, like predators and parasitoids, from “bad bugs”, which are insect pests like planthoppers. The strategy should also show them non-chemical alternatives to fighting the bad bugs.
“Insecticides are still a powerful weapon in the fight against insect pests, but farmers need good advice on what chemicals to use in what quantities and at what times (and also on when NOT to use chemicals),” he stressed.
“In Asia, insecticides are often marketed by small shopkeepers who sell them as fast-moving consumer goods alongside products such as shampoo and soap. Training of these shopkeepers and other retailers will enable them to provide farmers with the right advice. A licensing system for selling pesticides would help regulate and control the market.”
In the field, Bouman urged farmers to use crop rotation and diversication, synchronous planting and the use of sufficiently long fallow periods. They should also deploy resistant and tolerant varieties judiciously by using a combination of varieties that differ in their resistance or tolerance mechanisms, and by avoiding the use of the same varieties for more than two consecutive years to prevent pests developing resistance.
Ecological engineering
He also advocated “ecological engineering” as a measure for farming communities, by introducing landscape elements like flowers to promote the build-up and sustenance of a healthy population of parasitoids and predators.
“[Rice research institute] IRRI and its GRiSP partners in Asia are pioneering the introduction of ornamental flowers and agricultural plants such as okra and sesame on bunds in rice fields to attract the good bugs to help control planthoppers.
“Ecological engineering not only helps combat planthoppers but also enhances the scenic quality of the environment, can provide additional income, and may attract bees that can stimulate a local industry of honey production.”
However, Bouman warned that farmers and governments are still “grappling” with the mixed blessings of pesticides. Even though alternatives are available, their are less marketable.
“This requires a concerted effort by the public and private sector, scientists, farmers, policymakers, extension agents, and pesticide companies to make it happen.”