Insecticidal potency

When developing novel pyrethroids, particularly for household insecticides for indoor use, attention should be paid not to place too much importance on insecticidal potency and ease of use while giving sufficient consideration to the indoor persistence of chemicals and safety. 

Pyrethrin II was also detected in young leaves 2 months after seeding, similarly to pyrethrin I, but the content remained at about 0.05 wt% without seasonal change for 2 years. The insecticidal potency of pyrethrins obtained from pyrethrum leaves was confirmed with Musca domestica. 

Transfluthrin (30) [39] is a compound obtained by esterification of dichlorovinyl chrysanthemic acid with 2,3,5,6-tetrafluolobenzylalcohol. With very high insecticidal potency against mosquitoes and flies, it is used as a household insecticide however, as the promotion activity of the compound is known, its use should be restricted to preparations in which the issues of safety for humans and pets have been resolved. 

Natural pyrethrins, derived from pyrethrum, contain six insecticidal components. Due to their excellent insecticidal potency against insects in small amounts and their high safety for mammals, they are the only natural insecticidal components used for more than 100 years to date throughout the world as a household insecticide. 

However, we are concerned about the behavior, safety, and environmental problems of photostable synthetic pyrethroids remaining in and around houses, considering the present situation of their increased indoor use. In particular, compounds with strong insecticidal potency need long-term safety and residue studies for the health of infants and pets. 

Pyrethroids are a class of synthetic insecticides designed and optimized based on the structure of the pyrethrins found in natural pyrethrum extracted from chrysanthemum flowers [1, 2], Pyrethroids are widely used to control insect pests in agriculture and public health because of their relative safety for humans and high insecticidal potency [3]. 

Since 1995 some new types of pyrethroids with high insecticidal potency have been developed for practical use. For this reason we decided to publish a volume written by experts in various fields to review the development of new pyrethroids and offer future perspectives. This volume includes chapters on the progress and the future of pyrethroids, the biosynthesis of natural pyrethrins, newly developed polyfluorobenzyl-type pyrethroids with potent insecticidal activity, the mode of action, mammal toxicology, biotransformation and enzymatic reactions, environmental behavior, and ecotoxicology of pyrethroids. We hope that this book will contribute greatly to the further development of pyrethroids. 

The chief interest of petroleum chemists in the information presented here may be in the fact that, although the earlier kerosene type of petroleum derivatives mixture will produce insecticide fogs—and is still used successfully for them—an analysis of fog production and its use, from biological, physical, chemical, and mechanical standpoints, has resulted in the evolution of special fog oils which combine higher DDT solvency, specific insecticidal potency, greater safety, and greater chemical and physical stability with consequent limited and therefore more desirable particle size range, at known temperatures and pressures. 

S. Isayama, S. Saito, K. Kuruda, K. Umeda, K. Kasamatsu, Pyridalyl, a novel insecticide potency and insecticidal selectivity, Arch. Insect Biochem. Physiol. 58 (4)... 

The high insecticidal activity of Du 19111 against the larval stages of several lepidopterous, coleopterous and dipterous insects and its unique mode of action prompted us to synthetise several hundreds of benzoylphenyl ureas and to evaluate their insecticidal potency in laboratory tests and small scale field trials (4, >, j6). These and other studies led to the ultimate choice of diflubenzuron (il) as the optimal derivative for further development. 

The metabolism of neonicotinoids in vertebrates, insects, and plants has many common features. It may result in cleavage and the separation of the heterocyclic and pharmacophore moieties, or modifications of a pharmacophore in an intact parent molecule. Oxidations, reductions, and elimination reactions are the major mechanisms that result mostly in a reduced or diminished insecticidal potency of the metabolites. Dehydration of the 4-hydroxyimidazolidinyl resulting in a formation of the imidazolinyl (olefin) or reduction of the N-nitroimine ( = N—NO2) to N-nitrosoimine ( = N—NO) group (Figure 5) are examples of a... 

Hadaway, A.B., Barlows K and Duncan. J. (1963). Effects of piperoryl butoxide on insecticidal potency. Bull Eniomot. Res. 53. 769-777. 

Maintenance of high insecticidal potency while minimizing fish toxicity (e.g., the non-ester silafluofen)... 

One of the cleanest and most general reactions undergone by trivalent phosphorus compounds occurs with sulfur (177). For example, tri-alkylphosphines react vigorously with sulfur to yield trialkylphosphine sulfides. The analogous reaction of phosphorus esters has received considerable attention as a synthetic method, due largely to the insecticidal potency of the phosphorothioate esters. 

These compounds were tested against a series of Lepidoptera imder standard laboratory procedures. Activity on diamondback moth (PluteUa xylostdla, Px), fall armyworm (Spodoptera frugiperda, Sf), and tobacco budworm (Heliothis virescens, Hv) was evaluated. Insecticidal potency is reported as the LCjq in ppm. Comparison of the insecticidal activity for compounds D1-D3 identifies several key structural features of importance (Table 1). Our initial lead compoimd D1 was effective on the species S/and Px with LCjq values of 68.9 and 16.8, respectively, but with no activity on Hv. Incorporation of a 2-methyl group on the benzamide,... 

Table I. Insecticidal potency of anthranilic diamides against three species of Lepidoptera. ...

Sf, Spodoptera frugiperda Px, Plutella xylostella Hv, Heliothis virescens Insecticidal potency is reported as an in ppm based on larval mortality from leaves treated with serial concentrations of the experimental compounds at 96 hours post-infestation. 

Table II. Insecticidal potency and CMT values of anthranilic diamides D11-Dl 7.

The lead compound, which initiated interest in the neonicotinoids, is a nitro-methylene heterocycle, nithiazine (Figure 1) [1]. Nifhiazine, with its unique nitromethylene moiety, showed low mammalian toxicity, but its insecticidal potency and field stability were inferior to commercial organophosphates and pyrethroids. Thus, nithiazine was not of commercial use for pest control. However, the introduction of 6-choloronicotinyl and 2-nitroimino-imidazolidine moieties led to the development of the first commercial neonicotinoid imidacloprid (Figure 1)... 

Structural modifications of 4 regarding the substitution pattern of the TFM moiety, modification of nitrogen substituents or variation of the pharmacophore have indicate that this results in drastic changes in insecticidal potency [65] and that the incorporation of structural fragments known from previous neonicoti-noid insecticides does not necessarily lead to compounds retaining higher activity. 

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