Use In Europe As An Extract Of Sophora Flavescens Bioinsecticides

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The scientific literature continues to document the biological diversity of plant secondary metabolites that are known to affect pest insects. Botanicals have a long history of use and are referenced in recordings from ancient civilizations and folklore.1,2 Likewise, the natural history of insect-plant chemical interactions spans the past 400 million years, or as some authors like to say, terrestrial plants have engaged in chemical warfare against insects and other herbivores over that vast period of time. Therefore, to the non-expert, it would seem intuitively obvious that higher plants should be a source of unique natural chemicals with potential utility for the anthropocentric management of insects and related pests. Indeed, prior to the discovery of the insecticidal properties of DDT in the middle of the 20th century, some of the most important insecticides used in agriculture and related industries were of botanical origin. Almost completely displaced by synthetic insecticides in the DDT era, interest in botanicals was rekindled in the 1970s once the detrimental effects of synthetic insecticides on human and environmental health were fully realized.3

RSC Green Chemistry No. 11 Green Trends in Insect Control

Edited by Oscar Lopez and Jose G. Fernandez-Bolaiios © Royal Society of Chemistry 2011

Published by the Royal Society of Chemistry, www.rsc.org

At the same time, interest in the chemistry of plant secondary metabolites and their ecological roles blossomed, spawning a voluminous scientific literature on the effects of plant allelochemicals on insects that is growing exponentially at present. For example, according to the Web of Science database, a search for "plant extract and insecticidal activity'' in mid-2010 generated a list of 62 journal papers over the five year interval from 2005-2009; searching for "essential oils and insecticidal activity'' yielded 115 papers over the same interval ( = 23 papers per year), and the key words "botanical insecticide" yielded 116 papers.4 Much of the prior research in this field has been reviewed extensively, in volumes such as Insecticides of Plant Origin,5 Phytochemicals for Pest Control,6 Botanical Pesticides in Agriculture,7 Phytochemical Biopesticides8 and Biopesticides of Plant Origin.9 Given the effort and resources expended in this area of scientific investigation over the past 35 years, it would be reasonable to ask - has much of this knowledge found its way to the actual practice of pest management? And if not, why not?

The simple answer to the first question is that this vast body of scientific inquiry has generated only a handful of commercially viable pest management products (viz. azadirachtin, essential oils), at least in North America, Western Europe and Japan. At the same time, some areas of pest management have been transformed through the genetic modification of crop plants, the discovery of new and powerful insecticides of microbial origin, and the discovery of new and potent synthetic insecticides with novel modes of action and dramatically reduced risks to human health and the environment. Botanical products rarely match conventional synthetic or microbial insecticides in terms of absolute efficacy, speed of action, or cost - considerations of the utmost importance to farmers whose crop production practices have long included conventional pesticides.3 This is not to say that botanical insecticides cannot be useful in highly mechanized or intensively managed agricultural systems. In certain crop-pest contexts, botanicals have been shown to have an efficacy comparable to conventional pesticides as stand-alone products, but the former products may have greater utility in tank mixes with conventional products, in rotation with conventional products (to mitigate the development of insecticide resistance in pest populations), or for early season application in conjunction with augmentative biological control when pest pressures are low.10

In regions and countries where product standardization and consistency, and regulatory scrutiny are not as rigorous (compared to the G7 countries), many more botanical insecticides are being produced and used in agriculture. For example, several companies in China produce insecticides based on the qui-nolizidine matrine, obtained from the roots of Sophora flavescens (Fabaceae), and these products are exported to several other Asian countries (see Table 7.1). In India it is often mixed with other botanical products, synthetic insecticides or microbial insecticides, although it can be used as a stand-alone product.11 Another botanical insecticide produced in China contains nicotine and toosendanin, the latter a limonoid obtained from the bark of the Chinaberry, Melia azedarach (Meliaceae).12 In Thailand, more than a dozen locally produced botanical insecticides are used, including those based on

Table 7.1 Botanical insecticides currently in use on a commercial basis.

Pesticide

Source plant (s)

Major constituent (si*

M ode ( s) of action against insects

Region where cultivated

Pyrethrum

**LD50= 1400 mg kg"1 Neem

LD50= >5000 mg kg"1 Essential oils LDso = 4400-5100 mg kg" (limonene)

Nicotine

Rotenone

LD50 = 39.5-102 mgkg"1 Ryania

LDso =1200 mgkg"1

(powdered stems) Sabadilla

LDso = >5000 mg k"1 Quassia

LDso = 800 mgkg"1

(quassin) Matrine

LDso =1200 mgkg"1 (Sophora alkaloids) Toosendanin Mouse LDso = 250-500 mgkg"1

Tanacetum einer ariaefolhim Azadirachta indica many, esp. families Lamiaceae,

Myrtaceae, Lauraceae, Poaceae Nicotiana species

Derris, Lonchocarpus Ryania speciosa

Schoenocattlon officinale

Quassia, Aeschrion, Picrasma

Sophora flavescens Melia azedarach

Major products

Pyrethrins, jasmolins, cinerins

(chrysanthemic acid esters) Azadirachtins, other limonoid triterpenes Monoterpenes and sesquiterpenes

Nicotine, related alkaloids

Minor products

Rotenone, related isoflavones

Ryanodine (alkaloid)

Cevadine, veratridine

(alkaloids) Quassin (triterpene lactone)

Matrine (quinolizidine alkaloid)

Toosendanin (limonoid)

Axonic poisons (sodium channel agonists) Moulting inhibitors (ecdysone antagonists), antifeedants Neurotoxins (octopamine agonists), repellents

Neurotoxin (acetylcholine agonist)

Mitochondrial cytotoxin

Neuromuscular poison (calcium channel agonist)

Axonic poisons (sodium channel agonist)

unknown unknown

Antifeedant, stomach poison

Kenya, Tanzania, Ecuador,

Australia India, West and East Africa,

Central America, Brazil worldwide worldwide

Southeast Asia, South

America Caribbean

Latin America Venezuela, Brazil

China

China

*see Figures 7.2 and 7.3 for structures of these major constituents.

**LD50 values are representative of rat acute oral toxicity, unless otherwise noted.71"73

lemongrass oil (Cymbopogon species; Poaceae), saponins from tea (Camellia sinensis; Theaceae), and Stemona alkaloids (Stemonaceae).13 In many (perhaps most) tropical and subtropical countries in Asia, Africa and Latin America, a wide variety of indigenous crude plant preparations are often used to thwart insect pests in fields, in stored food and in human habitations. Indeed, it can be argued that use of these indigenous botanicals by subsistence farmers is of far greater value than the use of more refined botanical insecticides in more advanced agricultural systems in the Northern Hemisphere.14

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