Insecticides plant materials

Phenazine-l-carboxamide (137) is known as oxychlororaphine and has been isolated from cultures of Pseudomonas chlororaphisit has some limited inhibitory properties, but the inhibitory action of phenazines is generally disappointing. Some phenazine derivatives have insecticidal properties thus, phenazine itself has been found to be toxic to the clothes moth, the Hawaiian beet webworm, the rice weevil and larva of the codling moth, but under trial conditions its toxicity to plant material, as evidenced by severe burning of foliage, was found to be too high to make it of practical value. 

Y Williams. Carbamate insecticide residues in plant material Determination by gas chromatography. Residue Reviews 38 1-21, 1971. 

Some examples of the types of procedures used to determine insecticides and pesticides in plant materials are given below. 

Table 8.2. Determination of insecticides and pesticides in plant materials (from author s own files)... 

Carbaryl has been widely used as an insecticide on lawns or gardens. It has a low toxicity to mammals. Carbofuran has a high water solubility and acts as a plant systemic insecticide. It is taken up by the roots and leaves of plants so that insects feeding on the plant material are poisoned by the carbamate compound in it. 

Insecticides may act on direct contact with immediate effect or via the stomach of the insect with delayed efficacy. They can be deposited on surfaces or can be incorporated into the plant (systemic effect), killing the insects only when they feed on the plant material. 

Lime (calcium oxide) is widely used in the production of cement, steel, medicines, insecticides, plant and animal food, soap, rubber, and many other familiar materials. It is usually produced by heating and decomposing limestone (CaCOs), a cheap and abundant mineral, in a calcination process ... 

Some botanical insecticides are made by grinding raw plant materials, such as flowers, roots, stems, or seeds. Others are extracted from plant materials, then refined, purified, and packaged for sale. 

This is what we did at the American Cyanamid Research Center in Princeton, when we purified methyllycaconitine (an insecticidal plant alkaloid active on insect nicotinic receptors) from Delphinium plants. As reported by Dr. Chalmers in the Tuesday afternoon session, we were able to employ the in vitro cholinergic receptor binding assay to follow the active material present in small quantities on TLC plates. Results were available in a matter of hours. This type of strategy could expedite purifications of active materials from other natural sources. Also, knowing the mode of action of the insecticidal component at an early stage facilitated our decision to purify the active material. 

More elegant analytical methods exploit substances biological or biochemical properties. This is simple for acetylcholinesterase-inhibiting pesticides. Acetylcholinesterase is easy to measure, and the enzyme may be bought from suppliers or extracted from flies, earthworms, or vertebrate nervous tissue. The enzyme may be measured with and without addition of the extract containing the insecticide. Some plant materials may contain natural cholinesterase inhibitors (e.g., solanine in potato) that will interfere with this analysis if not removed. 

Veratrum plant material has also been used as an insecticide (Greenhill and Grayshan, 1992). Protoveratrine B (86) is a feeding deterrent to Syntomis larvae veratrine (94) is a feeding deterrent for Schistocerca (Wink, 1993). 

Atropine, the racemate of (S)- and (R)-hyoscyamine, is formed during the extraction of plant material. Although ( S)-hyoscyamine is more effective than the (/ )-enantiomer, atropine is more widely used for traditional reasons. In medicine, atropine is used against spasms during a biliary colic, as antidote against intoxication with organophosphorous insecticides, and as pre-medication before surgery to decrease salivation and respiratory secretion. (iS)-Scopolamine... 

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