Insecticides translocation

CaH24N.,03P2,(Me2N)2P(0)0P(0)(NMe2)z. It is not highly toxic to insects when used as a contact insecticide, but is readily absorbed by the roots and leaves of plants and translocated in the sap, so that the plant becomes toxic to species feeding on it. 

In this type of activation, which occurs in both animal and plant tissues, the original insecticide is relatively stable and can be translocated through plant tissues without destmctive hydrolysis until the oxidation has occurred, which then makes the insecticide both highly toxic and relatively unstable so that it rapidly is hydroly2ed to nontoxic products. 

The purpose of this work was to determine the toxicity to mosquito larvae of insecticide spray residues. That certain insecticides are translocated in plants (4, 5) adds impetus to this study. Fresh orchard fruit sprayed or dusted with preparations containing parathion (0,0-diethyl O-p-nitrophenyl thiophosphate), tetraethyl pyrophosphate (TEPP, HEPP), DDD [2,2-bis(p-chlorophenyl)-l,l-dichloroethane], DDT [2,2-bis(p-chlorophenyl)-l,l,l-trichloroethane], chlorinated camphene, and basic lead arsenate were shipped from California to Yonkers, N. Y., by air express for bioassay. 

In the field of organic phosphorus compounds there is a wealth of highly toxic compounds from which to pick a potential insecticide. The ultimate choice will be based not only on toxicity to a certain group of insect species, but on volatility, stability, safety in handling and applying, and freedom from plant injury, spray-residue and translocation hazards, and long-term toxicity to man and animals. 

The absorption of the ether bis(2-fluoroethoxy)methane from the soil and its translocation in plants in a concentration sufficient to kill insects is a recent discovery heretofore observed only in some selenium compounds and in the insecticidal esters of some polyphosphoric acids (4) Whether this property is shared by other organofluorine compounds will doubtless be determined for the purpose of studying plant metabolism and of evaluating any practical application. 

Modified from Markin, G.P. 1981. Translocation and fate of the insecticide mirex within a bahia grass pasture ecosystem. Environ. Pollut. 26A 227-241. 

The term systemic insecticide was introduced4 in connexion with compounds that are absorbed by the plant and translocated to other parts of the plant in such quantities that they have insecticidal action. 

Endolytic. After absorption in the plant and translocation the compounds are present to at least 98 per cent in their original form, and act in this form as insecticides until they are ultimately decomposed by the plant. 

The phenomenon of translocation within the plant has been widely studied and W. A. L. David, using 32P O.M.P.A. on broad beans, cabbage, hops, peas and strawberries has shown that the insecticide passes preferentially into the young parts of the plants, and upwards rather than downwards, although translocation in the downward direction does exist. Thus translocation of systemic insecticides has been attempted for the control of root aphis (e.g. lettuce root aphis). 

The organophosphorus compounds constitute one major group of insecticides, and a certain portion thereof may be transported to the aquatic environment resulting either from the actual use on paddy fields or from unavoidable transmittance to waterways. However, possibly because of its relatively shorter persistence, the translocation and transformation of organophosphorus compounds in the aquatic environment has not been extensively investigated as compared with more persistent organochlorine compounds. 

Biological. [ C]Phorate degraded in a model ecosystem consisting of soil, plants, and water (Lichtenstein et al, 1974). Under both nonpercolating and percolating water conditions, 12% of the applied amount migrated downward as the corresponding sulfone and sulfoxide. Phorate was absorbed in the roots of corn and was transformed primarily to the sulfone with trace amounts of the sulfoxide. Translocation of radioactive insecticide to the leaves was also observed but the major products were identified as phoratoxon sulfone and phoratoxon sulfoxide. 

There is, however, one means of achieving the conflicting properties required for apoplastic transport without resort to compromise. This is by using precursors which have characteristics favouring uptake and are then converted within the plant to active toxicants which are more readily translocated. The principle is best illustrated by the long-established organophosphorus insecticides of the systox type such as demeton, disulfoton and phorate which are relatively lipophilic... 

The half-life of the phosphamidon was a few days and by 4 days post spray, the insecticide was no longer detectable. The rapid loss of the material was attributed to weathering, breakdown, growth dilution, absorption and translocation within the tree. 

Systemic insecticide, absorbed by roots, with translocation to all parts of the plant... 

There are other advantages, too. With lower levels of insecticide, wildlife are not apt to be affected and environmental problems associated with pesticide use, e.g., groundwater contamination and pesticide translocation, will definitely be diminished or eliminated. 

Neurotransmitters are removed by translocation into vesicles or destroyed in enzyme-catalysed reactions. Acetylcholine must be removed from the synaptic cleft to permit repolarization and relaxation. A high affinity acetylcholinesterase (AChE) (the true or specific AChE) catalyses the hydrolysis of acetylcholine to acetate and choline. A plasma AChE (pseudo-AChE or non-specific AChE) also hydrolyses acetylcholine. A variety of plant-derived substances inhibit AChE and there is considerable interest in AChE inhibitors as potential therapies for cognition enhancement and for Alzheimer s disease. Organophosphorous compounds alkylate an active site serine on AChE and the AChE inhibition by this mechanism is the basis for the use of such compounds as insecticides (and unfortunately also as chemical warfare agents). Other synthetics with insecticidal and medical applications carbamoylate and thus inactivate AChE (Table 6.4). 

Granular formulations are used almost exclusively as soil treatments. They may be applied either directly to the soil or over the plants they do not cling to plant foliage. They may be used to control pests Uving at or below ground level or they may be absorbed by roots and translocated throughout the plant. The latter are, for the most part, either systemic insecticides or systemic herbicides. 

In the aphid M. perslcae, molecular evidence that insecticide resistance results from amplification of an esterase (E4) gene was provided following successful isolation and use of cDNA clones for the esterase. The degree of amplification of the structural gene was correlated with the activity of the esterase and the level of resistance. Quantitative differences between restriction patterns in different clones of resistant aphids were found to be correlated with the presence or absence of a specific chromosome translocation and with production of the esterase (22). 

This compound has unique systematic properties and is translocated both upwards and downwards in plants. Applied to the soil surface it has been shown to control soil-bom nematodes. In addition, it has an insecticidal effect. 

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