Insect toxicity

Alkali-Stable Polychloro Organic Insect Toxicants, Aldrin and Dieldrin... 

During the past 30 months two new compounds, aldrin and dieldrin, possessing great usefulness as insect toxicants, have been devised, synthesized, and studied in the laboratories of Julius Hyman Company. Both compounds are completely impervious... 

Kearns, Weinman, and Decker rate the more common halogenated insect toxicants in the following order of decreasing toxicity (7) dieldrin, aldrin, heptachlor, 7-hexachloro-cyclohexane, chlordan, toxaphene, and DDT. This rating follows as the result of rather extensive tests on ten species of insects and is believed to represent, in general, the order of their relative activity. 

In order to evaluate the actual magnitude of the insect toxicity of aldrin and dieldrin and the utility of these new compounds, additional data must be considered. (Many of the data herein presented have been obtained from letters and other unpublished communications. The details of the entomological investigations thus represented will, in most instances, be published in appropriate journals by their authors.)... 

The effectiveness of the insect toxicant aldrin to a wide variety of cotton pests has been determined through a large number of field tests. As a result of these tests, recommendations have been published suggesting the use of a mixture of 2.5% aldrin and 5%... 

Aldrin, like chlordan, exhibits residual effectiveness under field conditions for somewhat less than 3 weeks. Even when aldrin is applied at the uneconomical and unnecessary rate of 5 pounds per acre, leafy material so treated exhibits only slight insect toxicity after 3 weeks. Aldrin, therefore, falls into that class of materials which exhibit pronounced initial toxicity but relatively short residual action. 

The situation with respect to dieldrin is altogether different. No insect toxicant hitherto available, with the exception of DDT, has been characterized by the possession of insect toxicity which continued for long periods after its application. In this respect, dieldrin is unique in that, in addition to its high order of insect toxicity, it possesses a span of residual activity comparable to that of DDT. 

The residual effectiveness against flies of a number of formulations of insect toxicants was studied by investigators of the U. S. Public Health Service. Over a 2-month period the formulations containing dieldrin were found to give the best results (5). 

Two new insect toxicants, aldrin and dieldrin, provide new halogenated insect toxicants with an extremely high order of toxicity toward insects, combined, for the first time, with complete stability to alkalies. Under all the usual conditions of use these new toxicants are also stable to acids. Data illustrate the order of magnitude of the insecticidal activity of these materials and their utility. Aldrin is a relatively nonresidual material, in contrast to dieldrin which, because of its high persistence, exhibits prolonged residual activity. 

The recent announcements of the insect toxicants Compound 118, 1,2,3,4,10,10-hexa-chloro-l,4,4a,5,8,8a-hexahydro-l,4,5,8-dimethanonaphthalene (IV) (1, 15), and Compound 497, l,2,3,4,10,10-hexachloro-6,7-epoxy-l,4,4a,5,6,7,8,8a-octahydro-l,4,5,8-dimeth-anonaphthalene (V) (15) are of further interest. The official name aldrin has been designated for material containing at least 95% of IV, and dieldrin for material containing at least 85% of V. 

A colorimetric procedure is described for the determination of small amounts of Compound 118 (1,2,3,4,10,10-hexa-chloro - 1,4,4a,5,8,8a - hexahydro - 1,4,.5,8 - dimethano-naphthalene). Reaction with phenyl azide to form a di-hydrotriazole derivative and subsequent treatment with diazotized dinitroaniline in strongly acid medium produce an intense red color. Amounts of the insect toxicant of 10 to 40 micrograms in the final 10-ml. aliquot are readily determined with a spectrophotometer. Commonly used insect toxicants do not interfere. 

T he synthesis of an alkali-stable highly potent insect toxicant, tentatively called Compound 118, has been announced recently (2). Structurally Compound 118 is 1,2,3,4,10,-10-hexachloro-l,4,4a,5,8,8a-hexahydro-l,4,5,8-dimethanonaphthalene (I). The chemistry and applications of this material have been discussed by Lidov, Bluestone, Soloway, and Kearns (5). 

The aforementioned series of reactions provides a basis for a colorimetric analytical method for Compound 118 in which the commonly used agricultural chemicals do not interfere. The procedure described herein permits the estimation of as little as 10 micrograms of Compound 118, and has been successfully applied to the analysis of this insect toxicant in insecticidal dusts, in film residues on glass and paper, in human and animal urine, and in mixture with other insecticides. Application of this procedure to the determination of Compound 118 in milk and in spray and dust residues on plants appears promising. 

The commonly used organic insect toxicants do not interfere in the analysis of Compound 118 by this new procedure. Hexane solutions of chlordan, DDT, methoxychlor, hexachlorocyclohexane (BHC), and toxaphene treated according to the procedure for determining Compound 118 gave a pale yellow color similar to that of the blank. 

Fenvalerate is extremely toxic to representative nontarget aquatic organisms and to some beneficial terrestrial arthropods at concentrations substantially lower than those recommended to control pestiferous insects. Toxic effects are associated primarily with the 2.S, a.S -isomcr and are exacerbated at low temperatures. Birds, mammals, and terrestrial plants are normally tolerant. 

A newer class of insecticides is the pyrethroids. These are synthetic derivatives of pyrethrins, which are natural extracts from chrysanthemums. Pyrethroids have been developed to be more stable (and thus more effective as insecticides) than the pyrethrins, which are particularly instable in light. Pyrethroids are frequently used as broad-spectrum insecticides. They have high insect toxicity, but lower mammalian toxicity than their organophosphate or carbamate counterparts. Pyrethroids are still limited in effectiveness due to their environmental lability, their high cost, and their potential for resistance development. 

Devise a strategy to avoid or delay the onset of insect resistance using chemicals (both insect toxic and behaviour modifying), predators and parasites and transgenic crops ... 

The multiplicity of abiotic transformation products which have been detected for aminocarb has prompted a comparison of the anticholinesterase activity, in vivo insect toxicity and relative volatility of a series of oxidation products. Successive oxidations of the aryldimethylamino group resulted in increased toxicity whereas oxidation of the arylmethyl group or of the carbamate N-methyl group considerably reduced toxicity. Saturated vapour concentrations of the toxic transformation products were only slightly lower than the parent carbamate. 

Efrapeptins such as efrapeptin D (24 in Figure 5) were isolated from the entomopathogenic fungus Tolypocladium niveum. They have a unique linear peptide structure with a bicyclic amine moiety at their C-terminus and show insect toxicity by inhibiting mitochondrial ATPase.7... 

As can be seen from Table I a substantial number of alkaloids display significant insect toxicity, including nicotine, pipeline, lupine alkaloids, caffeine, gramine, strychnine, berberine, ephedrine, and steroidal alkaloids. Only the specialists can tolerate the respective alkaloids. The tobacco homworm (Manduca sexto), for example, can grow on a diet with more than 1% nicotine without any adverse effects. Most of the nicotine is either degraded or directly eliminated via the Malpighian tubules and in feces 182). Because nicotine binds to the acetylcholine (ACH) receptor, it is likely that in Manduca this receptor has been modified in such a way that ACH can still bind, but not nicotine (so-called target site modification). 

The toxic effects of alkaloids in insects (Table I) can be caused by their interference with diverse cellular and intracellular targets. Since most mechanisms have not yet been elucidated for insects, this issue is discussed below in the section on vertebrate toxicity (see Table IV). With some caution we can extrapolate to insect toxicity. 

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