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Plant-derived insect repellent
Most of the plant-based insecticides, whether used alone or in combination, not only reduced the rate of pests and plagues, but also significantly reduced the weight of pods compared with the control group. This indicates that the phytochemical insecticide not only interferes with pest feeding but also protects the leaves. , but also have a significant impact on the growth and development of larvae and metamorphosis. This makes sense for delaying or preventing insecticide resistance to insecticides and controlling the population of pests. After long-term coordinated evolution between herbivorous insects and plants, the diversity of the relationships formed between them cannot be explained because each insect exhibits a series of adaptability to its host plants; Hazard, a toxin that was previously produced by the plant chemist himself as a plant secondary compound, formed a self-defense checkpoint. As early as the 19th century, it was pointed out that: No plant has been able to feed on all herbivorous insects, and it has been observed later. It has repeatedly proved that certain food-eating insects have a tendency towards host plants and are addicted to food, and the tropism of non-host plants is not. Significant or repellent, refuse to feed even when exposed to starvation conditions. It was also found that the selection of host plants by herbivorous insects was due to secondary biomass contained in different plants (such as scopolamine, strychnine, methacroline, azadirachtin, and HUB The propyl propyl ester, pepper ketone, etc.) generally have the effect of preventing insects from feeding, causing them to abandon the plant or refuse to feed. For example, the adaptation of insect mouthparts to morphological characteristics and the changes in behavior and metabolic types that occur in response to physiological and biochemical characteristics of host plants. Although insects can tolerate or detoxify certain plant secondary biomass present in host plants, most of these substances present on other plants still function as toxins. Some people describe insects like an analytical chemist who can identify various chemicals encountered in their surroundings and identify foods and toxins. According to the physiological characteristics of insects and the fact that many plants in the natural world are protected from many insects due to bad smell, it was found that the leaves of the banyan tree contain substances that can strongly inhibit the feeding of the famous herbivorous desert cricket (Schistocerca gregaria). . Inspired by this discovery, it is believed that it is possible to seek compounds from plants as insecticides for feeding or laying eggs to control pests and protect crops. In recent years, due to the increasing demand for environmental quality, the side effects of some common insecticides due to residual problems, and the emergence of insect resistance. Therefore, these environmentally friendly pesticides are increasingly valued by chemists. Among them, research and development of plant-derived insect repellents have attracted particular attention. l. Insect repellents are generally considered to have an effect on the behavior of insects by stimulating attracting of insects for attracting or spawning attractants and stimulating insect avoidance to reduce repellent feeding or spawning, but such Classification cannot accurately describe the multiple behavioral responses of insects to compounds. In order to accurately describe the effect of the compound on insect movement, feeding, and spawning, it can be further divided into arrest, stimulant, attractant, repellent, and deterrent. Dethier believes that the act of causing insects to avoid evasive reactions is called repellent, and can be further divided into repellents and antifeedants according to the physical state of the compounds; in the same year, Kennedy pointed out that repellent reactions of insects are divided into random movements of insects (irregular motions). ) and movement away from chemical sources directly, insect repellent behavior is not a simple behavioral response, but should be the sum of a sequence of neural and behavioral responses. Repellent behavior should be divided into fast and slow or strong and weak, The probability of repellent and antifeedant insects appearing on the treated surface is considered to be divided. Dethier later stated that the response of insects to compounds can be divided into the movements directly away from the chemical source and the excitement of insects and the number of occurrences on the treated surface. The former is called repellent and the latter is called antifeedant. Insect feeding activities include biting the first, swallowing, and continuing feeding. Some people argue that the compound that inhibits the first bite is called inhibin, and the one that blocks further feeding is called hindered hormone. Because it is often unclear at what stage the feeding activity is being repressed, many authors will refer to the substances that prevent or interrupt the feeding of insects when they come in contact. Modern people use the term antifeedant to summarize inhibitors and inhibitors. The so-called antifeedant is a kind of compound that can make the insects permanently lose their ability to feed until they are starved to death, rather than kill it directly. If the insects are no longer fed, until they starve, the antifeedant is called an absolute antifeedant; the antifeedant that does not starve the insect is called a relative antifeedant. The above definition of the antifeedant is only defined from the apparent form of the insect, and the definition of the insect antifeedant from the physiological reaction of the insect is that the external nerve changes the behavior of the insect (ie, acts directly on the chemoreceptor) to cause feeding. Substances that are hindered by the process are called antifeedants, that is, the antifeedants can suppress the taste receptors of insects, affecting the recognition of food by insects, or stimulating the insects' anorexia receptors to cause insects to resist feeding. This definition excludes those chemical substances that inhibit the feeding process through the action of the central nervous system. Repellents do not belong to the category of antifeedants because the term repellents is used to include the directional movement of insects away from the source of the stimulus, ie to disperse them with their own special odors before the insects contact them. Volatile compounds. 2. Species of plant-derived insect repellents Plants are the most abundant source of organic compounds on the earth. Although only 10,000 secondary plant metabolites have been identified in the chemical structure, it is estimated that the total number of plant compounds can reach more than 400,000. Plant-derived substances with anti-feeding characteristics can be found in virtually all chemical types, such as terpenes, alkaloids, coumarins, flavonoids, terpenoids, phenols, glycosides, xylans, and woods, Some steroids, polyacetylenes and some amino acids, but mainly some quinones (including monoterpenes, sesquiterpenoids, diterpenoids and triterpenoids) and alkaloids. Including triterpenoid azadirachtin, sesquiterpenoid Hua Bomu suppositories, strychnine alkaloids, furanocoumarin anisotrope propyl ester, diterpenoid Hydroxygrindelic acid, neo lignans Pepper ketone. A plant may contain one or more compounds having antifeeding activity. 3. Characteristics of plant-derived insect repellents Antifeedants certainly have all the advantages of indirect insecticides, of which the most notable advantage is their high efficiency and non-toxicity. The activity of indirect insecticides on pests is generally highly specific. This means that beneficial insects (such as bees) and predators are safe even if they eat such compounds. At the same time, specificity also makes pests less resistant to insecticides. Capinera et al. [7] pointed out that antifeedants should actually have the following main properties: (1) should be more durable; (2) transfer to non-treated parts through plants; (3) have no harmful effects on non-target organisms. The ideal antifeedant should be absorbed and transported by the plant so that the newly grown part of the plant can be protected. All chewing, sucking or drilling insects can be contacted with this compound while other insects will not be affected. Prof. Van Beck from Dutch Agricultural University detailed the characteristics of antifeedants, which are listed below: (1) Non-toxic to plants; (2) Non-toxic to humans, animals, beneficial insects and other organisms; (3) Preventing as much as possible Pests invade; (4) work on specific pests; (5) activity at low concentrations; (6) long-lasting efficacy; (7) no toxic or odor metabolites; (8) can be absorbed or metabolized by plants; (9) easy to use; (10) cheap and easy to obtain; (11) does not conflict with other control methods; (12) does not change the taste, size or appearance of the product; (13) does not make the insect pest resistant; (14) Stable storage. 4. Effects of plant-derived insect repellents on feeding behavior The feeding behavior of herbivorous insects depends to a large extent on whether the food meets the needs of insect nutrition or the food lacks compounds that inhibit feeding, or both. . However, if any one of the two exists, it will affect the feeding of insects. It is well known that sucrose can stimulate many insects to feed on food. Many food-eating insects require the presence of specific compounds in their host plants. For example, several oligophagous insects on cruciferous plants require glucosinolates to stimulate their feeding, and non-host plants contain non-host plants that inhibit their feeding. Compounds, and polyphagous insects, are a result of the lack of compounds in many host plants that inhibit their feeding. Insect feeding activities are affected by the presence of many compounds, and many insects may perceive even subtle changes in a stimulus and use this recognition ability in feeding behavior. 5. Physiological effects of plant-derived insect repellents During the long-term evolution of plants, three types of chemical defenses against insects have been formed: (1) causing insects to repel and inhibiting their feeding; (2) affecting the digestion of food by insects. And utilization; (3) poisoning or dying insects or delaying their growth and development [1]. Plants contain a variety of secondary metabolites that can kill pests and protect themselves by affecting the insect's nervous system, respiratory system, muscle system, digestive system, reproductive system, and growth and development. Researchers believe that insect repellents generally affect insect feeding from the level of sensory perception. The perception of insect antifeedants may include different mechanisms that may stimulate specialized receptors or alter the activity of receptors in other compounds, thereby altering the sensations. Obviously, the types and numbers of susceptors of different insects are different. More precisely, each insect has its own sensation that is unique to its surroundings. Because of this unique system, it is physiologically best suited to distinguish between host and non-host plants [8][16]. Although the sensilla of different kinds of insects often overlap each other, there are no two species that are completely consistent in the nature of feeding. Some people studied the behaviors and neurophysiological mechanisms of five Lepidoptera larvae through a biguanidae antifeedant, suggesting that the reason of antifeedant is not the enzyme-substrate type but mainly affects the receptor cell membrane. And these results are explained as follows: The triterpenoids irritate and suppress most or all of the so-called feeding cells. It is also believed that the thiol-containing protein group on the susceptor film plays a decisive role in the antifeedant. This stimulation pattern varies depending on the type of insect and is more or less affected by the compound. Antifeedants mainly act on the sensilla on the antennae of the insects, on the lower whiskers, or on the lower lip whiskers, interfering with these sensory devices transforming the characteristics of the food into electrical signals and transmitting it to the central nervous system, resulting in antifeedants. Antifeedants can significantly inhibit the feeding of insects and have a relatively slow insecticidal effect. Generally, after 3 to 6 days of drug use, significant insecticides appear. The feed intake of pests gradually decreased with increasing concentrations. At higher concentrations (100 μm / mL Chuanxiongsu), the pests only bite tiny defects on the margins of the leaves. After that, the insects did not feed at all until the hungry. And die. At the lower concentration (250-600 μm / mL Chuanxiongsu), less food was taken, and as the starvation time prolonged, the feed intake of pests gradually increased. And the test worms were fed multiple times, but each time they ate less. 6. Prospects for the application of plant-derived insect repellents As an outstanding representative of antifeedants, azadirachtin has been put into the commodity market, and it has been favored and has achieved very good economic and social benefits. Azadirachtin has prominent advantages in terms of high insecticidal activity, broad insecticidal spectrum, and diversity of mechanism of action in the prevention and control of sanitary pests, warehouse pests, and vegetable pests. At low concentrations, azadirachtin can prevent males and females from recognizing sex pheromones or mating abnormally. It can also cause endocrine disorders, larvae, larvae, and phlegm to become permanent larvae or death. It can also protect pests in vivo. The titers of juvenile hormone decrease, yolk can not be deposited, ovarian tube atrophy and malformation; at high doses, the gluttonous larvae of the chewing mouthpart can be prevented from feeding, so that the number of insect pests can be reduced to achieve the purpose of controlling pests, and It has no pollution to the environment, it is safe to natural enemies of pests, and pests are not susceptible to drug resistance, which fully meets the requirements of comprehensive management. Therefore, many experts predict that antifeedants have broad application prospects in integrated pest management [12]. Environmentally safe pest control methods - Antifeedants have gradually attracted attention as part of sustainable agriculture. However, to fully utilize the role of insects' antifeedant compounds in the natural world, it is necessary for phytochemical workers and insect workers to establish a good cooperative relationship. Insect workers are responsible for conducting biometric work with clear objectives, reliability, and reproducibility, providing the basis for phytochemical workers to isolate active ingredients from the plants being studied. From the present point of view, insect insect repellents cannot constitute the last tool for pest control, and at best it is only an auxiliary measure for pest control in some cases, but from the point of view of the need to continuously develop new pest control agents, people The enormous potential of antifeedants cannot be ignored either. It can be foreseen that the development prospects of insect antifeedants are very broad because antifeedants do have many unique advantages and show good ecological, economic and social benefits. And with the rapid development of genetic engineering, the idea that plant's antifeeding genes will be transferred into crops will soon be realized. For example, the gene that forms the potato beetle antifeedant Leptine compound has been introduced into potato from wild plants and has become a resistant plant by cell culture. This research further expands the application prospect of insect antifeedant compounds. However, humans currently lack the basic knowledge of the exact mechanism of action of antifeedants, insect chemistry and physiology, and the impact of antifeedants on ecosystems. For the plant-derived insect repellent to play an important role in IPM, there is still a lot of work waiting for us to do it.