K.L. Heong, International Rice Research Institute, Los Baños, Philippines
K. H. Tan, Retired Professor of Entomology, Malaysia
Neonicotinoids or “neonics”, developed in the 1990s, are neurotoxin insecticides that specifically block the nicotinic acetylcholine receptors in the insect nervous system, but not the muscarinic acetylcholine receptors which are more abundant in mammals. They have lower toxicity in mammals than insects although some breakdown products are toxic. Imidacloprid is now one of the most widely used insecticide in the world, particularly in rice ecosystems. However, because of misuse a rapid development of insecticide resistance had occurred; and it had fallen from “hero to zero” (Tan 2009) – contrary to “zero to hero” by Jeschke and Nauen, 2008). In China, use of imidacloprid, sold in more than 500 trade names in the rice ecosystems, has declined because rice hoppers have developed insecticide resistance exceeding 300 folds.
Publications in SCIENCE and NATURE and about 50 other studies published in specialist scientific journals over the past two years all showed a consistent pattern of high risk to bees in the normal use of neonicotinoids. These chemicals are killing pests, bees and hymenopera parasitoids during spraying and uses as seed dressing. In addition, at low levels they interfere with insect behavior due to “brain damages”. Two papers in Nature Communications and the Journal of Experimental Biology discuss these details. The European Parliament in 2012 published “Existing Scientific Evidence of the Effects of Neonicotinoid Pesticides on Bees”, and concluded that the risk to bees after normal applications of neonicotinoids is not acceptable. In Sichuan, China, some apple and pear orchards had to employ human pollinators due to lack of natural insect pollinators. Albert Einstein once said:
“If the bee disappeared from the surface of the globe then man will only have four years of life left”.
On 29 April 2013, the European Union voted to suspend for a two- year period 3 neonicotinoids (imidacloprid, thiamethoxan and clothianidin) for use in flowering crops where bees forage. Details are found here. Recently, a paper described a deleterious link between imidacloprid and aquatic fauna. They showed a significant negative relationship between macro-invertebrate abundance and imidacloprid concentration for all species pooled. A significant negative relationship was also found for several insect orders, namely, Amphipoda, Basommatophora, Diptera, Ephemeroptera and Isopoda which are non pests but beneficial species serving as important detritivores, alternative preys to generalist predators as well as predators themselves. Aquatic fauna in rice ecosystems provide valuable “pest invasion” ecosystem services.
In 2011, US researchers demonstrated that imidacloprid caused spider mite outbreaks through increasing fecundity and destroying its insect predators, and thus, relaxing natural regulatory mechanisms against the mite. Additionally, in May 2013 the same group of researchers found that applications of neonicotinoid insecticides have been associated with outbreaks of spider mites in several unrelated plant species. The study showed that the insecticide disrupted plant defenses and linked it to increased population growth of a non-target herbivore. Do neonics also disrupt plant defenses in rice crops and make them vulnerable to planthopper outbreaks as well? Rice planthoppers are secondary pest species with similar ecological characteristics as spider mites. The high potential of imidacloprid and other neonics in causing outbreaks can similarly trigger brown plant hopper (BPH) outbreaks in rice production.
Imidacloprid has fallen from being a hero to “zero” and now a potential “villain”. Although the neonics are being phased out in China’s rice production and suspended in EU, marketing of these chemicals in Asia has instead increased in intensity. Will this unprecedented increase in use of neonics be beneficial to or seriously threatening agriculture in Asia?
The neonics are available in the market either singly or in cocktails under hundreds of trade names. Some common ones include Actara, Agite, Alika, Adage, Centric, Cruiser, Flagship, Meridian, Platinum, Vifone, Virtako, Gaucho, Admire, Merit, Poncho, Votivo, Confidor, Solomon, Provado. Many local names are given to mixtures using neonics and many more product names in Chinese, Thai, Vietnamese and Indonesian.
Jeschke, P. and Nauen, R. 2008. Neonicotinoids – from zero to hero in insecticide chemistry. Pest Manag. Sci. 64: 1084-1098.