Arthropods agents

Phenoxazines — The microbial phenoxazines like actinomycins are well-known antibiotics. Actinomycin D produced by Streptomyces anibioticus is an effective antineoplastic agent that inhibits nucleic acid synthesis. The main function of ommochromes is to act as screening pigments in the eyes of insects and other arthropods, as pattern pigments in the integument, and as excretion products of excess tryptophan. ... 

There are known to be about 30,000 disease-causing agents (fungi, viruses, nematodes, bacteria) in 3,000 types of cultivated plants. More than 10,000 species of arthropods (insects, ticks, arachnids) affect agricultural plants and animals. Along with agriculture, pesticides are also widely used in forestry and fisheries, in energy and railroads (to clear plants), in construction (to protect wood structures), etc. 

The preceding falls far short of conveying a true impression of the chemical skills of arthropods. Excluded from our discussion are the diverse signaling agents that mediate such vital insectan functions as food location, mate attraction, social bonding, and alarm communication. Other contributors to this colloquium address some of these topics. While... 

Foil, L.D. and Gorham, J.R. 2000. Mechanical transmission of disease agents by arthropods. In Medical Entomology (B.F. Eldridge and J.F. Edman, eds), pp. 461-514. Kluwer, Dordrecht. 

This dual activity against both nematode and arthropod parasites of animals was an unexpected bonus from a screen for anthelmintic agents. The reason for this broad activity lies in their mode of action. They act by interfering with y-aminobutyric acid (GABA) mediated neurotransmission. When treated with avermectin, the nematode Ascaris suum becomes paralyzed although it retains normal muscle tone (17). Picrotoxin, an antagonist of GABA, can reverse the effect of avermectin on neurotransmission vitro. 

The microorganism was classified as a new species of actinomycete. Streptomyces avermitilis. Its anthelmintic activity was shown to reside in 8 closely related macrocyclic lactones, named avermectins, which were also found to possess activity against free-living and parasitic arthropods. One of the natural components, avermectin is now being evaluated as a pesticide for the control of mites of citrus and cotton crops and control of the Red Imported Fire Ant. A chemical derivative, 22,23-dihydroavermectin or ivermectin, has been developed as an antiparasitic agent. It is being marketed for use in cattle, horses and sheep and is expected to become available for swine and dogs. 

It is the purpose of this chapter to discuss the neuroeffector, octopamine, and its related biochemistry in the arthropod nervous system as a target area for the rational discovery of control agents in the light of the criteria listed in Table I. 

The known and postulated actions of OA in arthropods have been the subject of several recent reviews (8 9 12t13) and will be mentioned here only in as far as it helps to indicate the kinds of responses which may occur when octopaminergic drugs are presented to an arthropod, and how some of these responses may be utilized to develop assays for the discovery and evaluation of such agents. 

Adverse hygienic conditions favor human infestation with multicellular organisms (referred to here as parasites). Skin and hair are colonization sites for arthropod ectoparasites, such as insects (lice, fleas) and arachnids (mites). Against these, insecticidal or arachnici-dal agents, respectively, can be used. Endoparasites invade the intestines or even internal organs, and are mostly members of the phyla of flatworms and roundworms. They are combated with anthelmintics. 

Mechanism of Action A scabicidal agent that is directly absorbed by parasites and ova through the exoskeleton. Therapeutic Effect Stimulates the nervous system resulting in seizures and death of parasitic arthropods. 

Although any microbe that infects a human (virus, bacteria, fungus, etc.) could theoretically be considered to be a parasite, the term parasite tends to be reserved for three types of infectious agents protozoa, helminths, and arthropods. These may be subdivided as follows ... 

Guo, Chang, Li and Douglas82 have used 19F—NMR spectra and found that a 10% oxyhemocyanin (arthropod) solution caused a 38.7 Hz increase in the line width observed for a 0.125 M KF solution. That effect occurs without displacement of 0 2 from the oxyhemocyanin. Agents such as thioacetamide which induce conformational changes in the protein leading to the expulsion of 02 also expel fluoride ion from the active site even though F" is evidently bound in the active site quite differently than 02. 

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