Chapter 2
Botanical Insecticides: A Global Perspective Downloaded by CENTRAL MICHIGAN UNIV on November 25, 2014 | http://pubs.acs.org Publication Date (Web): October 23, 2014 | doi: 10.1021/bk-2014-1172.ch002
Murray B. Isman* Faculty of Land and Food Systems, University of British Columbia, Vancouver, British Columbia V6T1Z4, Canada *E-mail:
[email protected].
According to the CAB Direct database of scientific publications, there has been enormous growth in research on botanical insecticides over the past 30 years. In 1980 less than 2% of all journal papers on insecticides dealt with botanicals whereas that proportion exceeded 21% in 2011. In particular there has been explosive growth in studies on insecticidal properties of plant essential oils; over half of the 2,200 papers on essential oils as insecticides have been published since 2006. In contrast, commercialization of botanical insecticides has continued to proceed at a relative snail’s pace, indicating a big disconnect between theory and practice. This is certainly the case in the jurisdictions with the most rigorous regulatory standards – the EU, USA and Japan. Using California as an example, use data for botanical insecticides also suggests a very modest market presence. According to Cal DPR data from 2011, botanicals constituted only 5.6% of all biopesticides used, and less than 0.05% of all pesticide use. However some recently introduced products have seen modest success. On the other hand, there appears to be increasing commercialization of botanical insecticides in China, Latin America and Africa, regions where socio-economic conditions have led to some of the worst examples of human poisonings and environmental contamination. Arguably, botanicals should be of greater value in developing countries where the useful plant species are often locally abundant, accessible and inexpensive. In many tropical countries semi-refined plant preparations are likely to be
© 2014 American Chemical Society In Biopesticides: State of the Art and Future Opportunities; Coats, et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2014.
relatively safe for users and more cost effective than imported conventional crop protection products. In G20 countries botanical insecticides will probably remain niche products for use in public health, urban pest control and in organic food production, but with considerable market opportunities.
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Introduction Insecticides continue to be the cornerstone of insect pest management, both in agriculture and in non-agricultural situations. And while regulatory requirements for approval of new insecticides have grown increasingly stringent in industrialized countries, a wide range of insecticidal products have been developed in the past twenty years that pose far fewer risks to human health and the environment. Among the types of insecticides that meet “reduced risk” criteria are microbials and microbial products, insect growth regulators, recent generations of synthetic insecticides, and botanicals – insecticides derived from plants. Plants produce a bewildering array of “secondary metabolites” – substances not involved in primary metabolism, but instead thought to play an ecological role in relationships between plants and other organisms. Perhaps a thousand or more of these substances have some demonstrated biological activity in insects, at least in laboratory tests. These include compounds with behavioral actions – those causing repellence, feeding deterrence or oviposition deterrence – and those with physiological actions – those causing acute toxicity, developmental disruption or growth inhibition. It is not uncommon for a plant secondary compound to have both behavioral and physiological effects in one insect species, or different effects in different species. Increasing academic interest in botanical insecticides was recently documented in a bibliometric analysis of scientific literature on this topic (1). Between 1980 and 2012, the proportion of published papers on botanical insecticides among all papers published on insecticides increased from 1.43% to over 21%. In absolute terms, the numbers of papers on botanical insecticides has grown over the same period from less than 100 per year to over 1100 per year. Much of that growth can be attributed to the voluminous literature (>5000 papers) on neem-based insecticides (based on the Indian neem tree, Azadirachta indica) starting in the mid-1980s, and since 2000, to papers on plant essential oils as insecticides. Of the approximately 2200 papers published through 2012 on essential oils as insecticides, over half were published since 2006. But commercialization of botanical insecticides has not kept pace with this explosive growth in academic studies that should provide the scientific foundation for the development of such products. In this chapter I discuss the current status of botanical insecticides on a global scale, as well as divergent regulatory environments that are impeding or facilitating the use of such products in different jurisdictions. 22 In Biopesticides: State of the Art and Future Opportunities; Coats, et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2014.
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Current Status of Botanical Insecticides in the U.S.A. Following the Second World War and the remarkably successful commercialization and implementation of synthetic organochlorine, organophosphate and carbamate insecticides, only a handful of botanical insecticides remained in use for the subsequent four decades. These included pyrethrum (from flowers of Tanacetum cinerariaefolium), rotenone (from rhizomes of Derris elliptica), nicotine (from foliage of Nicotiana tabacum), sabadilla (from seeds of Schoenocaulon officinale) and ryania (from stemwood of Ryania speciosa) (2). In recent years, the use of rotenone as an insecticide has declined and it is principally used at present as a commercial piscicide. Nicotine has fallen out of favor owing to its acute toxicity and high risk to humans. Sabadilla and ryania are little used at present. Among these original five botanicals, pyrethrum remains the only product in considerable use in the U.S.A. Some previous issues of uncertainty in supply of pyrethrum oleoresin, formerly sourced primarily from East Africa, have been mitigated by more recent large-scale production of pyrethrum in Tasmania, Australia. Two “new” botanical insecticides entered the U.S. marketplace in the past two decades, namely, neem-based insecticides and plant essential oils. Neem insecticides (herein defined as organic extracts of de-oiled neem seed cake, rich in azadirachtin) were first registered by the EPA in 1990 and are now represented by at least half a dozen products. These have, however, not enjoyed a great deal of commercial success in the U.S.A., in part owing to their relatively high cost, and in part to their relatively slow action against target pests. On the other hand, neem insecticides are produced and used on every continent. Plant essential oils were first commercialized as botanical insecticides in the late 1990s, facilitated enormously by the inclusion of specific common oils (viz. rosemary, cloves, cinnamon, lemongrass, thyme, mint) on the EPA’s List 25B of “Exempted Active Ingredients” (3). This legal distinction allowed products to be commercialized without meeting the EPA’s normal regulatory requirements, saving manufacturers millions of dollars and years in development. This opportunity was best exploited by EcoSMART Technologies Inc. who have become the industry leader in this area, with products for professional pest control, agriculture, animal health and consumer markets. One notable exception is an insecticide/acaricide (Requiem™) based on terpenoids from wormwood, Chenopodium ambrosoides originally developed by Codena Inc. and later licensed to AgraQuest Inc. This product, approved and registered by the EPA, became part of the pesticide portfolio of Bayer CropScience when that company acquired AgraQuest in 2012. To put these products in context, it is valuable to examine actual use data. In general such data is hard to come by (or very expensive to acquire), but the California Department of Pesticide Regulations maintains scrupulous records of all pesticides used in that state and publishes the data annually in a pesticide use report that is freely accessible from their website (www.cdpr.ca.gov). This is a particularly relevant database in that (i) California produces >400 agricultural commodities, including nearly one-half of all US-grown fruits, nuts and vegetables; (ii) California is the largest producer of certified organic crops in 23 In Biopesticides: State of the Art and Future Opportunities; Coats, et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2014.
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the U.S.A., producing >50% of organic fruit and vegetable crops in the country; (iii) California accounts for ~22% of all agricultural use of pesticides in the U.S.A.; and (iv) growers in California tend to be progressive – willing to try new products and technologies. Data for all pesticides used and selected groups of pesticides in 2006 and 2011 are shown in Table I.
Table I. Pesticide Use (Pounds Active Ingredient Applied) in California
a
2006a
2011a
All pesticides
187,754,207
191,969,313
Biopesticides
1,180,830
1,600,636
-- Microbials
260,885
259,300
-- Oilsb
422,444
611,800
-- Botanicals
56,130
83,100
data from refs. (4, 5)
b
includes clarified neem oil.
Within that five-year window, overall pesticide use (measured as pounds of active ingredient applied) increased by 1.7%, whereas the use of biopesticides increased by 35.6%. Within the biopesticide class, use of microbials remained stable (-0.6%), while oils increased by 44.8% and botanicals increased by 48.0%. Although the growth in biopesticides and botanicals appears quite impressive, their scale of use is less so. Overall, biopesticides constituted
