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BOTANICAL INSECTICIDES: REFLECTIONS AND PERSPECTIVES John E. Casida Environmental Chemistry and Toxicology Laboratory, Department of Environmental Science, Policy and Management, University of California, Berkeley, California 94720-3112, USA Importance and History. Insects are our main competitors for a limited supply of food and fiber. Pests destroy about one-third of the world food supply during growth, harvesting and storage, even with the use of pesticides and other control measures. The insecticides have evolved from inorganics to botanicals to synthetic organics. The inorganic insecticides have almost disappeared from use on crops for reasons of inadequate effectiveness and safety. The botanicals and synthetic organics have many similarities yet important differences and limitations. The author presents some reflections and perspectives on these relationships from a half century of personal experience in insecticide research. Five Major Botanicals. There are five major botanical insecticides, i.e. pyrethrum, rotenone, nicotine, neem and ryanodine. Pyrethrum extract from the flowers of the white daisy Chrysanthemum cinerariaefolium is the most important. The countries of production include Kenya, Tanzania and Australia. The effectiveness is enhanced and the economics improved by adding piperonyl butoxide for stabilization from metabolic detoxification in insects. Pyrethrum is also important because its active ingredients, the pyrethrins, provided the model for the synthetic pyrethroids which now constitute 20% of the market value of all insecticides. Rotenone from the roots of Derris elliptica and Lonchocarpus utilis has for 150 years been used to control chewing insects and as a piscicide to kill unwanted fish. Rotenone has been the prototype for Complex I respiratory inhibitors but not for economically successful structural modifications. Home gardeners recommend rotenone use. Nicotine, the alkaloid of tobacco plants (and cigarettes), has declined in use for decades but serendipitously served as the mode of action but not structural prototype of the new synthetic neonicotinoids of high effectiveness and apparent safety. Neem has important local uses in India and China and the extract with azadirachtin active ingredient is an effective crop protectant acting as an antifeedant. Ryania is the ground stemwood of Ryania speciosa. The supply is limited but the effectiveness is high for lepidopterous larvae. Supply and Composition. One of the limitations of botanical insecticides is consistent supply with adequate standards of effectiveness and safety. This is a constant challenge even with the best producer organizations. Pyrethrum once had an allergen now removed by a defined cleanup procedure. We analyzed cubé resin (the commercial rotenone supply) and found 11 stilbenes and flavonoids and 29 rotenoids (including one that incorporated chlorine from the solvent extraction conditions). Nicotine has been extensively studied except perhaps its environmental degradation products. Neem contains many active ingredients; we described nimbolide and epoxyazadiradione as cytotoxic agents. The principal active ingredient of Ryania was long described as ryanodine until we found that 9,21-dehydroryanodine was of even greater importance. Toxicology. Botanicals are more difficult to evaluate toxicologically than synthetic insecticides. They usually have one or two major active ingredients (e.g. pyrethrins I and II in pyrethrum extract) but there may also be many related bioactive compounds (e.g. in neem). Unless highly purified they also have hundreds to thousands of other extractives or natural products which can vary with the plant source and processing. Critical evaluation of toxicology requires production and use samples of consistent composition. Toxicology studies on pyrethrum extract meet current standards but those for other botanicals are lacking in scope, although this does not necessarily mean hazards are involved. Residues of botanical insecticides are rarely a known problem. The pyrethrins photodecompose rapidly to compounds of greatly reduced neurotoxicity. The same applies to the rotenoids and ryania components. Natural products are generally considered to be easily metabolized. They have few or no halogens or refractory substituents. Quite the contrary they have phenol, alcohol and ketone substituents, and alkene moieties that are amenable to ready degradation. The analyses are more difficult than with most synthetics: the lack of halogens limits the analytical detector sensitivity; multiple components and related but inactive analogs complicate the process. Mode of Action and Resistance. Mode of action is an important aspect of insecticide use, safety and toxicology. The same targets are involved in the most part with the botanicals and synthetics. Major insecticides act on four principal targets in the nervous system. PDF creato con FinePrint pdfFactory versione dimostrativa http://www.secom.re.it/fineprint 8
target botanical synthetic sodium channel – pyrethrins DDT, pyrethroids voltage dependent chloride channel - picrotoxinin* cyclodienes, lindane, GABA-gated fiproles acetylcholinesterase physostigmine* organophosphates methylcarbamates nicotinic receptor nicotine neonicotinoids *never a major commercial insecticide The synthetics indicated above constitute about 90% of the insecticide market. This has major implications in the selection for resistance leading to higher required doses and less effective control. Selection with the synthetics can lead to target site resistance to the botanicals, e.g. the use of synthetic pyrethroids and even DDT results in selection of strains resistant to pyrethrins. Prototypes. Botanicals and other natural products are primary sources and prototypes in the search for new insecticides. Screening of plant extracts enables the search of thousands of compounds as mixtures. This can be done at random or with knowledge of potential usefulness from practice or folklore. Bioassay-directed isolation and modern characterization techniques can often lead to a defined structure in weeks. This practice for a half century has turned up potent compounds usually with problems of inadequate selectivity for insects versus mammals. The variety and source of organisms are not infinite and limitations in this approach are already evident in the number of new isolates that turned out to be previously known components with insecticidal activity. Medicinal plants and herbs are frequently used or proposed to control insect pests. A literature search will usually reveal the active ingredient and often the mode of action. Isolation of the effective component will usually verify that one is using a new source of an old control chemical. The approach is still good but with increasing limitations. Botanicals are more likely than synthetics to give leads for completely new types of insecticides. With synthetics, the problem is to generate a new lead compound and then prepare massive numbers of analogs and rapidly optimize their structure. Combinatorial procedures help here. Fast throughput screening allows rapid sifting for effectiveness and mode of action. Organic Agriculture. Botanical insecticides and natural foods fit well together. Rapidly increasing knowledge helps choose the best materials and insures their effectiveness and safety. The natural chemical defenses of plants used as botanical insecticides offer continued benefits in organic agriculture with confidence that the consumer and environment will be adequately protected. PDF creato con FinePrint pdfFactory versione dimostrativa http://www.secom.re.it/fineprint 9
Page 1 and 2: International Congress BIOLOGICAL P
Page 3 and 4: 15:40-16:20 G. Lozzia Università d
Page 5 and 6: MAIN SPEAKERS • V. Rotondo FIAO,
Page 7: Il settore oggi è regolamentato in
Page 11 and 12: RELIABILITY AND PROSPECTIVES FOR TH
Page 13 and 14: Vineyard Passive diffusion Spontane
Page 15 and 16: of the host, a relatively limited n
Page 17 and 18: LOZZIA G.C., RIGAMONTI I.E., 1994 -
Page 19 and 20: DIFESA DELLE COLTURE DAI PATOGENI F
Page 21 and 22: THE FUNGAL PHYTOTOXINS AND THEIR PO
Page 23 and 24: NEED FOR RESEARCH AND APPROPRIATE A
Page 25 and 26: PRESENCE OF OCHRATOXIN IN EXPERIMEN
Page 27 and 28: 5. Hohler, D. (1998). Ochratoxin A
Page 29 and 30: Table 3: Pesticide treatments on
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Page 33 and 34: Xenorhabdus spp. and Photorhabdus s
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Page 39 and 40: PROTECTION OF GRAPEVINE FROM POWDER
Page 41 and 42: I MEZZI TECNICI PER L'AGRICOLTURA B
Page 43 and 44: POSTER 1. Agosteo G.E., Ambrosio M.
Page 45 and 46: 31. Pietri A., Bertuzzi T., Barbier
Page 47 and 48: 1 PROVE DI LOTTA ALL’OIDIO DELLO
Page 49 and 50: 2 LUPINUS ALBUS, AN ANCIENT EUROPEA
Page 51 and 52: Table 1. Benzo(a)pyrene and benzo(e
Page 53 and 54: 5 INSETTICIDI D’ORIGINE VEGETALE
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7 NATURAL COMPOUNDS IN THE CONTROL
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8 METHODS FOR EVALUATION, IN CONTRO
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Figure 3. Effect of Pseudomonas sp.
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9 IMPROVEMENT OF SOIL PROPERTIES AN
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(mg kg-1) (mg kg-1) 140 120 100 80
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10 NEMATICIDAL ACTIVITY OF AQUEOUS
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% cumulative hatch 40 35 30 25 20 1
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ROTENONE Il principio attivo è est
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- azadiractina nei confronti di F.
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Recovery and repeatabilty tests wer
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13 IMPIEGO DEL TIMOLO NEL CONTROLLO
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dello standard esterno. E’ stata
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Tab. III - Residui di timolo(mg/Kg)
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phytotoxicity index (%) Results In
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15 ORGANIC WHEAT QUALITY AND PRODUC
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16 IL CONTROLLO DELLA “ MOSCA DEL
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Nel primo anno si può notare un an
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17 Il contenimento della ticchiolat
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Obtained recoveries percent were: 8
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[Pb] (ng/g) 250,00 200,00 150,00 10
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Supelco Supelclean LC-18 SPE tubes
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12. Agullo, G.; Gamet, L.; Besson,
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Tab. 3 Flavonol content (µg/ml) in
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mg/L Fig.3 3,50 3,00 2,50 2,00 1,50
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Table 1 - Fungicides used during th
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Table 3 - Efficacy of different tre
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21 CONTAMINAZIONE DA MICOTOSSINE IN
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Ricerca: Aflatossine B1 B1+B2+G1+G2
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Campioni non Conformi 3,4 % B1 Camp
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22 PEPTIDATI DI RAME: PRODOTTI INNO
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23 CHARACTERIZATION OF ORGANIC VIRG
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24 CHARACTERIZATION OF ORGANIC VIRG
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25 EFFICACY EVALUATION OF BIOLOGICA
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Fig. 1 - Effects of Biological Cont
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26 IL CONTROLLO DELLE OPERAZIONI DI
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Results and Discussion S. carpocaps
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entompathogenic nematodes. CSC-EC E
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After this preliminary screening an
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FIGURE 3. Insecticidal activity of
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Several colonies of Lepidopteran, C
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M. Scribano research work was suppo
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Nematode isolate % Mortality 3 100
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In our trial organic wheat showed a
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per "strippare" i vapori nitrosi re
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L’ultima parte della ricerca è s
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33 INVESTIGATIONS ON THE BACTERICID
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Vengono qui riportati i risultati d
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while for dinocap is 10 pg/µL. For
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[Pb](ng/ml) Figure 1: Pb content of
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