Pyrethrums

PRENTOX , pyrethrum pesticides, 111 PRESPERSION PAB , zinc oxide, 111 Pressure Chemical Company, 245 PREVAIL , cypemietlu-in, 111 Priborlabs, 197... 

Bertram, m. pellitory (Anacyclus pyrethrum and similar plants). -(s)wur2el, -wurz, /. pellitory, pyrethrum (root of Anacyd.ua pyrethrum). 

The edible parts of parsnips contain a chemical of insecticidal and strong synergistic nature. This chemical, present in a concentration of about 200 p.p.m., was isolated and identified as 5-allyl-l-methoxy -2, 3-methylene-dioxybenzene or myristicin. Its toxicity to various insects (fruit flies, etc.) was established and compared with pyrethrum and aldrin. A second chemical, identified as 2-phenylethyl isothiocyanate, was found in the edible parts of turnips and rutabaga, which also have been consumed for centuries by humans without obvious harm. 

A review of the chemistry and biochemistry of pyre-thrum is presented based mainly on work done subsequent to 1945. The greatest advances in the chemistry of pyrethrum have occurred since the disclosure of the heterogeneity of pyrethroids. On the biological side, the most recent work has been made possible by the use of chromatographic column separation and gas chromatography separation of the four active components of pyrethrins. 

The great advance in the field of instrumentation, coupled with the discovery of the heterogeneity of the pyrethrolone radical, has advanced the knowledge of pyrethrum chemistry considerably beyond that known in 1945. LaForge and Barthel (24,25) have shown the structure of the active ingredients of pyrethrum, known collectively as pyrethrins, to be esters as represented by the structure shown in Table I. 

Recently a new constituent of pyrethrum extract was described by Godin et al. (9) jasmolin II, the cir-pent-2-enylrethronyl ester of pyrethric acid. Jasmolin II differs from pyrethrin II in that the terminal double bond of the alcoholic side chain is saturated. This constituent forms about 3% of the total pyrethrins. Jasmolin II is less toxic to the insects tested than a similar concentration of pyrethrins. The pyrethrum extract was 16 to 17 times as toxic as jasmolin II to Aedes aegypti and Fhaedon cochlearia adults, less than 17 times... 

Jasmolin II in pure form was nearly equal to cinerin II in toxicity to houseflies but much less when synergized. The synergistic factor of the synergized compounds is pyrethrum extract 9.6 jasmolin II, 7.0 cinerin II, 12.0. 

Godin et al. (10), working on the effect of insecticidal activity of pyrethrum flowers from fresh and dried flowers, showed that extracts from fresh flowers had little or no greater effect on pyrethroid content and insecticidal activity than extracts from dried flowers with drying temperatures up to 80 °C. However, some of all the pyrethrin was lost at 120°C. The principal loss was in pyrethin I and not pyrethin II. 

Sawicki et al. (33) prepared by reconstitution pure samples of pyrethrins I and II and cinerins I and II and compared the toxicity of these esters with the regular pyrethrum extract on houseflies 5 to 6 days old. 

Table II. Relative Toxicity of Pyrethrum LD50, and LD75 Levels Experiment A Constituents at LD25, Experiment B ...

A number of synergists are used with pyrethrum to increase its toxicity. Most of the better ones, as far as flying insects are concerned, are of the methylene dioxyphenyl type. The best known of this type is piperonyl butoxide. 

Piperonyl butoxide increases the absolute toxicity of the four constituents of pyrethrum. 

Table III. Relative Toxicity of Four Constituents of Pyrethrum at Six Ratios of Synergist to Active Ingredient...

The biochemistry or mode of action of pyrethrum is not as well known as its chemistry. There are several theories of the toxic action of pyrethrum. Lauger et al. (26) consider that a highly effective contact insecticide must possess a toxic component (toxaphore) and must have groups attached which absolutely insure pronounced lipid solubility. They consider in the case of pyrethrins that in the cyclopro-... 

Blum and Kearns (1) showed in the American cockroach that topically applied pyrethrum shows a negative temperature coefficient of action between 15° and 35°C. The 24-hour LDso for pyrethrum is about 1 g. at 15°C. and about 6 Mg- at 35°C. 

By employing C14-labeled pyrethrum, it has been determined that at 35 °C. the rate of penetration of pyrethrum is more than twice that at 15°C. Cockroaches prostrate at 15 °C. can be returned to normal by transferring them to 35 °C., a process which can be repeated for several hours. Since cockroaches transferred from 35° to 15°C. became prostrate more rapidly than those held continuously at 15°C., the insecticide (or some metabolic toxin) was probably in the vicinity of its site of action at 35 °C. but was ineffective. 

The development and adaptation of procedures for the separation, isolation, purification, identification, and analysis of the components of the pyrethrum mixture have been studied and evaluated. Results of studies to determine the molar extinction coefficient of pyrethrin I as well as a gas chromatographic procedure for the determination of pyrethrins are reported. The use of chromatographic separation procedures (including partition, adsorption, gas, and thin-layer chromatography), colorimetry, and infrared spectrophotometry are discussed. 

It is apparent from the literature on pyrethrum analysis that there is little agreement on what is needed or wanted in new methodology. As soon as it is possible to obtain complete information on all the significant components of the pyrethrum mixture, a better understanding of the methodology needed will be available. 

The purpose of this paper, then, is to summarize the present condition of some of the work done in this and other laboratories and present information on the separation, isolation, and identification of some of the components of pyrethrum. Work of others has, in part, been confirmed and some new evidence is presented on compounds isolated from the pyrethrum mixture. 

Column Chromatography. Liquid-liquid partitioning has been used by several investigators for several pesticides, including pyrethrum (1,2,3,5,10,13). The most useful procedure allows the... 

Partition column chromatography for separating several of the primary constituents of the pyrethrum extract has been reported. The elution pattern for some of the constituents of the pyrethrum mixture recovered from the partition column is shown in Table I. 

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