Larry L. Larson
Dow Elanco Discovery Research
9330 Zionsville Rd.
Indianapolis, IN 4628-1053
Novel Organic and Natural Product Insect Management Tools
Synthetic organic insecticides continue to be critical to the successful operation of pest management systems. These tools are effective, short duration, solutions when pests exceed our established thresholds and economic damage is occurring. The focus of the insecticide discovery and development efforts at various companies, however, has changed over the past decade. We are seeing the results of these changes in a particularly large number of selective pest control agents currently under development around the world. These new materials represent the beginning of a new era in both synthetic organic and natural origin pest control options. This era will be characterized by low use rate, highly effective, generally selective agents designed for tactical strikes. In many cases, these materials will require more management expertise, but will be far friendlier to the total environment including biological control organisms.
These new materials are the result of a pattern of innovation within industry that has been prompted by the public need for safer pesticide use. The total pounds of active ingredient used on US crops has been in decline since the advent of the insect managing synthetic pyrethroids in the 1970's and early 1980's (see Table 1). This decline has been pushed along by technological innovation and competition by the industry and greater use of pest threshold information in IPM programs. Together these factors have accomplished a dramatic reduction in insecticide usage not usually recognized by the general public. This reduction amounted to 51% less active ingredient used in 1991 than in 1979 according to US Environmental Protection Agency statistics (Gianessi and Anderson, 1993).
To track the course of the industry innovation over the last 20 years, materials tested in the Insecticide and Acaricide Tests (now the Arthropod Management Tests) 1975 and 1995 in the IA Tests (now AMT) were studied (see Table 2). These volumes are the best record of industry activity as they generally reflect university development programs supported by industry funds. The level of activity on various chemical classes in 5 year increments over the last 20 years were studied to look for trends.
The numbers of organophosphates, organotins, and chlorinated hydrocarbons peaked in 1975, the first year of the study. The numbers of citations for chlorinated hydrocarbons peaked in the 1980 sample while total numbers of materials peaked in 1975, the first year of the publication. Carbamate numbers peaked in 1980 and have been in decline ever since. The numbers of citations for organophosphates has consistently been higher than for any other class. The numbers of total materials peaked in 1975, the first year of the publication. Total citations peaked in 1980. Pyrethroid numbers peaked in 1990, but citations peaked in 1985. Bacillus thuringiensis products have shown a dramatic increase in numbers and citations in the 1990's becoming the second most cited class in 1995 and may not have peaked yet. In addition the 1990's has seen the resurgence of the nicotinoids with the discovery of imidacloprid by Bayer AG and the discovery of several new materials including: the mitochondrial electron transport (MET) inhibiting acaricides, the pyrolles, the fipronils, abamectins and the naturalytes. All of these newer materials have use rates considerably lower than the organophosphates, organotins, carbamates and chlorinated hydrocarbons of 1975.
The industry has also focused on more efficient use of traditional chemistry minimizing rates and maximizing target exposure through more effective delivery systems. An example of this is the new Sentricon Colony Elimination System for termites from DowElanco (Robertson and Su 1995). Subterranean termites account for 80 percent of the approximately $1.5 billion spent for termite control every year in the United States(Su, 1991). Barrier treatments at high use rates are generally used to prevent termite attack. These have very little effect on the termite colony and have to be broadcast uniformly to cover any potential entrance point. These sorts of applications often necessitate retreatments that can be difficult and costly(Robertson and Su, 1995). In 1989 DowElanco, in cooperation with Dr. Nan-Yao Su of the University of Florida, began a research program designed to evaluate hexaflumuron, a proprietary benzoylphenylurea insect growth regulator as a bait against subterranean termite species (see Table 3).
This cooperative program led to the registration of hexaflumuron as a termite control product in 1994.
Lufenuron (see Table 4) is a benzoylphenylurea from Ciba-Geigy currently being sold as an oral flea control product for small animals. It also has crop uses globally on cotton, vegetables, and fruit.
As a flea control agent it's systemic activity targets the dose lowering the use rate dramatically and virtually eliminates environmental exposure (Hopkins, 1994).
Imidacloprid (see Table 5) is a chloropyridinyl material from Bayer AG that acts as a nicotinoid.
It is highly effective systematically at 50-100 grams AI/Ha on a variety of sucking insects in fruits, vegetables and rice. Use as a systemic minimizes impact on beneficials. It also has a favorable toxicity and ecotoxicity profile (Hopkins, 1994).
Chlorfenapyr (see Table 6) is a pyrrole uncoupler from American Cyanamid.
It is effective on chewing and sucking insects and mites in cotton, vegetables, and fruits at rates of 50-300 grams AI/Ha. It is selective to beneficials due to its' predominantly stomach poison activity and so will have a place in insect and mite pest management (Hopkins, 1994).
Tebufenozide (see Table 7) is a diacylhydrazide ecdysone agonist from Rhom&Haas Company active at rates of 50-250 grams AI/Ha in fruits, vines, vegetables and forestry.
The original and selective mode of action together with a good toxicological; and ecotoxicological profile suggest that tebufenozide will be a valuable tool as a selective Lepidoptera control agent for the protection of tree and row crops (Hopkins, 1994).
Fipronil (see Table 8) is a phenyl pyrazole GABA agonist from Rhone-Poulenc active on chewing and sucking insects in row crops, vegetables and turf.
Use rates are from 25-150 grams AI/Ha and as a member of a new class of insecticides will be valuable in resistance management (Hopkins, 1994).
Fenazaquin (see Table 9), a quinazoline mitochondrial electron transport inhibitor from DowElanco is a broad spectrum acaricide for tree fruits, vines, and ornamentals.
It is effective at rates of from 56-560 grams AI/Ha. Its novel mode of action, short residual contact activity, lack of activity on predators, and safety to mammals and birds all make for an ideal mite management tool (Hopkins, 1994).
Pyridaben (see Table 10) is a pyridazinone mitochondrial Site I inhibitor from Nissan Chemical Industries Ltd. active on mites, aphids, whiteflies, and thrips of tree fruits.
Its use rates are from 50-200 grams AI/Ha. This material also shows a lack of predator activity and safety to mammals and birds allowing it to fit into mite management programs (Hopkins, 1994).
Pyriproxifen (see Table 11) is an alkoxypyrimidine juvenile hormone mimic active against scales and whiteflies on cotton, pome fruit, citrus, and vegetables from Sumitomo Chemical Company.
It is active at 25-100 grams AI/Ha and is very selective fitting well into Insect Pest Management systems (Hopkins, 1994).
Pymetrozine (see Table 12) is a pyridine azomethine antifeedent effective on Homopterous pests from Ciba Geigy Ltd.
It is effective at rates of from 100 to 300 grams AI/Ha. It's selectivity to the Homoptera makes it fit well into Homopteran pest management.
Diofenolan (see Table 13) is a dioxalane juvenile hormone analog with activity against scales and Lepidoptera in tree fruits from Ciba Geigy Ltd.
The original mode of action and good selectivity together with good toxicological and ecotoxicological profile make it especially useful for Integrated Pest Management (Hopkins, 1994).
Emamectin (see Table 14) is an abamectin semi-synthetic analog providing Lepidoptera control capabilities from Merck & Co. Inc.
As is the case with avermectin, it increases chloride ion flux at the neuromuscular junction. The targeted crops are row crops and vegetables at 5-25 grams AI/Ha. Due to the low to moderate contact activity of the material and rapid dissipation of surface residues most beneficial species are not effected. Thus the material is expected to fit Insect Pest Management Programs (Hopkins, 1994).
Spinosad (see Table 15) is a fermentation-derived natural product affecting receptors in the central nervous system of Lepidoptera, Diptera, Thysanoptera, and some Coleoptera and Hymenoptera from DowElanco.
Targeted crops are cotton, vegetables, tree fruits, and nuts at use rates of from 50-180 grams AI/Ha. In the field, safety to beneficials led to several instances in the 1995 Experimental Use Permit studies where fewer applications in cotton and tree fruits were necessary for secondary pest outbreaks on the spinosad plots. It is also safe to mammals, birds, and fish. Spinosad, with its unique characteristics, does indeed fit a class of its own, and will offer an exciting pest management alternative for the future. No other naturally sourced material has its combination of excellent contact and residual efficacy on target pests and safety to beneficials, aquatic organisms, and mammals. It will fit IPM in cotton, vegetables, and tree crops very well (Jantz et al, 1994).
Future Transitions for Organic IPM Tools
As reported by the US. EPA (see Table 16) the trend has been toward fewer organic Insect Management Tools being registered over time (Aspelin, 1994).
According to Stetter (1993), the numbers of materials required to find a new active is rising exponentially, probably due to higher standards necessary for product registration and market success (see Table 17).
Fortunately, driven by the pharmaceutical industry, synthesis and screening technologies continue to improve, allowing rapid synthesis and testing of a diversity of chemistries against insect selective targets. This technology promises to allow the industry to keep pace as we make the transition towards an exciting future with new IPM tools.
Due to changes in public perception and customer attitudes favoring higher activity and greater applicator and environmental safety, the industry has responded with more highly active and selective Pest Management Tools. These already have made a dramatic reduction in the pounds of conventional insecticide applied to crops in the US. The materials in the pipeline have never been more impressive and carry the promise for even better Pest Management Systems in the future. Sprayables will always be necessary to lower pest outbreaks and through the use of Pest Management techniques we can preserve these new tools for many years to come. Thanks to new innovations from a variety of companies, and better recognition of the value of IPM, the future for synthetic organics and natural products as tools for Pest Management has indeed never been brighter. However there are still no magic solutions. The crop protection industry will need to use resistance management and all available IPM tactics to stay ahead of our insect competitors.
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