Fish parasite has increased its resistance to abamectin
In recent ten years, abamectin insecticide preparation, which served as the antiparasitic agent that has broad spectrum and high efficiency, has been widely used in fishery and animal husbandry in the world and has obtained good evaluation. However, due to the sustained use of this kind of preparation, many endoparasite and ectoparasite, especially the parasitic helminths and arthropods have generated resistance year by year. As a result, the pesticide effect has reduced sharply and even lost its effect. Therefore, this problem has aroused great attention of the international experts and they are hunting for effective measures that can overcome or decrease the resistance.
This article is mainly about the discussion and conclusion on the research about the resistance to abamectin carried out by scholars from Canada and America as well as many people who work in the same industry in China, which is only for your reference.
Abamectin, a kind of macrolides disaccharide compounds, has contact action and stomach action on many parasites, which can interfere in the neural physiological activity as well as inhibit and paralyze the nerve conduction by stimulating the release of γ-aminobutyric acid. However, due to the long-term use of abamectin pesticide, the drug has combined with the corresponding receptor of the parasite cell, thus its affinity and drug susceptibility will be reduced, eventually, it will reduce the pesticide effect or lose effect. In addition, as the protein and enzyme activity that can eliminate the drug in the parasite cell is increased as well as the dominant gene will effectively inherit generation after generation, thus it will generate strong drug resistance, which will lead to the complete inefficiency of the drug in the end.
Moxidectin is developed on the basis of abamectin and ivermectin. Although these three kinds of products all belong to the marcrolides biological agent, moxidectin has higher antherlmintic activity, longer efficiency and is safer than abamectin and ivermectin, besides, it can kill the vivo and vitro parasitic arthropod and helminths with very low doses. Its chemical structure characteristics are as follows: introducing N-OCH2 gene on C23 place, reducing one disaccharide base on C13 and so on, thus its water solubility and lipid solubility will be 400 times higher than abamectin and ivermectin. Abamectin miticide that has poor water solubility, of which the molecular weight is more than 350, it is very difficult to penetrate into the insect body and play the medicinal effect. However, moxidectin has high lipid solubility, it can penetrate into the insect body surface chitin and enter the arthropod body and generate a series of physiological and biochemical reactions, for example, it can stimulate the release of GABA of insect body synapse and change the chloride channel and kill the insect. The test shows that after moxidectin enters into the insect body, the drug concentration in the parasite cuticula and corium is more than 6 times higher than the subcutaneous tissue and the inside body, which proves that it will effectively prevent the insects by sprinkling or pouring and splashing moxidectin. The research and application that carried out by Donglas and other people shows that by sprinkling low concentration of moxidectin on worms and arthropod louse, the validity period can last about more than 40 days, which has much larger pesticide effect than abamectin and ivermectin.
Doramectin is formed by connecting Ch cyclohexyl on C-25 of abamectin (which is same as 25-cyclohexane AVM-B1a), which has been considered as the best insect-resistant drug in the new type of abamectin family. It is used for killing a kind of worms in America, Brazil, Argentina, Venezuela, New Zealand and other countries, of which the effective rate can reach 99.5 percents and even reach 100 percents for some larva.
The insect-resistance mechanism of doramectin is as follows: the glutamic acid of the insect body will control the opening of chloride channel, meanwhile, the chloride ion will also lead to the hyperpolarization of nerve resting potential, thus the nerve conduction will be blocked, the nerve will be paralyzed and the insect will be killed in the end.
As this kind of new compound has higher activity than abamectin and also due to its long validity period, safety and low dosage, it has replaced abamectin and has become the best drug in preventing and killing vivo and vitro parasitic arthropod and helminths.
In addition, the insect-resistant biological agents that are produced by mutational biosynthesis including emamectin, eprimamectin and other drugs, they all have very obvious pesticide effect.
The application of compound preparation
It can be a kind of effective approach in developing new drug by compounding and combining various insect-resistant drugs into a kind of preparation that has lethality. Practices show that by compounding levomisole, fenbendazole, albendazole and so on, which all will increase effect in varying degrees.
The topical anti-insect agents include efficient cypermethrin, fenpropathrin, bifenthrin, fenvalerate, deltamethrin, biphenthrin, malathion, acephate, triazophos, fenitrothion, methamidophos, emamectin benzoate, benzoate and so on, which all have large synergism.
According to the statistics, as early as in the late 1980’s, America and South Africa discovered that parasites had generated resistance to abamectin. With more and more use of abaemctin afterwards, the resistance became strong until the drug lost its effect. Therefore, the relevant departments in various countries strengthened a lot on researching new drugs, besides, vaccine inoculation and gene inoculation methods were studied and applied so as to prevent the insect attack. In china, dipterex and imidacloprid that used in preventing the parasitic helminths and arthropods, has greatly reduced their pesticide effects and even lose the effect now. Artemisia toosedarin, a kind of compound preparation that is developed and screened recently, has special effect on preventing dactylogyriasis of eel. Besides, extensive test on this kind of drug has been carried out at present.