Necessary cookies are absolutely essential for the website to function properly. These cookies ensure basic functionalities and security features of the website, anonymously. The cookie is used to store the user consent for the cookies in the category "Analytics". The cookies is used to store the user consent for the cookies in the category "Necessary".
The cookie is used to store the user consent for the cookies in the category "Other. The cookie is used to store the user consent for the cookies in the category "Performance". It does not store any personal data. Functional Functional. Functional cookies help to perform certain functionalities like sharing the content of the website on social media platforms, collect feedbacks, and other third-party features.
Performance Performance. Performance cookies are used to understand and analyze the key performance indexes of the website which helps in delivering a better user experience for the visitors.
Analytics Analytics. Analytical cookies are used to understand how visitors interact with the website. These cookies help provide information on metrics the number of visitors, bounce rate, traffic source, etc.
Advertisement Advertisement. Advertisement cookies are used to provide visitors with relevant ads and marketing campaigns. These cookies track visitors across websites and collect information to provide customized ads. Others Others. Other uncategorized cookies are those that are being analyzed and have not been classified into a category as yet.
The cookie is set by GDPR cookie consent to record the user consent for the cookies in the category "Functional". The result has been the disappearance of many attractive ones that have never been serious weeds. Species such as wild delphinium Delphinium ajacis , pheasant's eye Adonis annua , corn cockle, Agrostemma githago and cornflower Centaurea cyanus , have come to the verge of extinction in Britain and can now only be found in abundance in the peasant agricultural systems of Eastern Europe.
Of particular importance are the effects of insecticides on the natural arthropod enemies of an insect pest. This, in itself, may not appear too serious, apart from the regrettable loss in the natural diversity of harmless species.
However, it can - and often has - had two extremely serious consequences. The first, target pest resurgence, refers to the rapid increase in pest numbers following some time after the initial drop in pest abundance caused by an application of insecticide. This rebound effect occurs when treatment kills not only large numbers of the pest, but large numbers of their natural predators too with any survivors likely to starve to death because there are insufficient pests on which to feed.
Then, any pest individuals that survive either because of resistance or good luck or that migrate into the area, find themselves with a plentiful food resource but few if any natural predators. A population explosion is the likely outcome because the predator requires the pest to be present to support population growth, but the pest certainly doesn't need the predator.
Another reason is tied into what makes a pest: they are likely to be able to reproduce rapidly when food resource becomes available and they have the ability to locate these resources, i. Hence, pests are likely to be good at resurging. When the natural predator cycle is broken, it is not only the target pest that might resurge.
Alongside any actual pest are likely to be a number of potential pest species, which are not pests only because they are kept in check by their natural enemies. Thus, if a primary pest is treated with an insecticide that destroys a wide range of predators and parasitoids, other species may realise their potential and become 'secondary' pests.
A dramatic example of this took place in Central America in ; when mass dissemination of organic insecticides began, there were two primary pests within cotton production: the boll weevil and the Alabama leafworm. Organochlorines and organophosphates applied fewer than five times per year initially had apparently miraculous results and yields soared.
By , however, three further pests had emerged, cotton bollworm, cotton aphid and the false pink bollworm. The application rate rose to times per year. This reduced the problem of the aphid and the false pink bollworm, but led to the emergence of five further secondary pests. By the s, the original two-pest species had become eight. There were, on average, twenty-eight applications of insecticide per year Flint and van den Bosch, On a broader scale, changes in the overall pattern of weed infestation can be seen as an example of the outbreak of secondary pests.
The herbicides in use until the s, when they were selective at all, tended to be most active against dicotyledonous weeds. The result has been an upsurge in the importance of grass weeds monocots , and the s therefore saw the beginnings of a new drive towards the production of herbicides selective against grasses Lockhart et al.
The final problem is, in many ways, the most serious one of all. Even before the advent of the organics, occasional examples of resistance to an insecticide had been found.
For instance, A. Melander in showed that scale insects demonstrated resistance to lime-sulphur sprays. Between and , eleven additional cases were recorded.
The development of organic insecticides, such as DDT, gave hope that insecticide resistance was a dead issue. However, by , just one year later, housefly resistance to DDT had evolved in Sweden. The evolution of pesticide resistance is simply natural selection occurring more rapidly than usual and on a particular obvious character. Within a large population subjected to a pesticide, one or a few individuals may be unusually resistant perhaps because they posses an enzyme that can detoxify the pesticide.
If such individuals exist at the outset, resistance can begin to spread in the population immediately; if they arise subsequently by mutation, then there will be a lag in the evolutionary response before this chance event occurs. In either case, the resistant individuals have an improved chance of surviving and breeding and, if the pesticide is applied repeatedly, each successive generation will contain a larger proportion of resistant individuals figure 3.
Figure 3. This graph presents the chronological increase in unique cases of herbicide resistant weeds. So, if a Conyza canadensis becomes resistant to atrazine Group C1 , it is listed as one unique case, if another population of Conyza canadensis becomes resistant to ALS inhibitors Group B , then it is counted as a separate "unique" case, but if a third population is found with multiple resistance to ALS and Triazine herbicides it does not count, as the other two already cover the sites of action.
One answer to the problem of pesticide resistance is to develop strategies of 'resistance management'. The first recorded use of insecticides is about years ago by Sumerians who used sulphur compounds to control insects and mites, whilst about years ago the Chinese were using mercury and arsenical compounds for controlling body lice 4.
Writings from ancient Greece and Rome show that religion, folk magic and the use of what may be termed chemical methods were tried for the control of plant diseases, weeds, insects and animal pests. As there was no chemical industry, any products used had to be either of plant or animal derivation or, if of mineral nature, easily obtainable or available.
Thus, for example, smokes are recorded as being used against mildew and blights. The principle was to burn some material such as straw, chaff, hedge clippings, crabs, fish, dung, ox or other animal horn to windward so that the smoke, preferably malodorous, would spread throughout the orchard, crop or vineyard.
It was generally held that such smoke would dispel the blight or mildew. Smokes were also used against insects, as were various plant extracts such as bitter lupin or wild cucumber.
Tar was also used on tree trunks to trap crawling insects. Persians used the powder to protect stored grain and later, Crusaders brought information back to Europe that dried round daisies controlled head lice 7. Many inorganic chemicals have been used since ancient times as pesticides 8 , indeed Bordeaux Mixture, based on copper sulphate and lime, is still used against various fungal diseases.
Up until the s inorganic substances, such as sodium chlorate and sulphuric acid, or organic chemicals derived from natural sources were still widely used in pest control. However, some pesticides were by-products of coal gas production or other industrial processes. Thus early organics such as nitrophenols, chlorophenols, creosote, naphthalene and petroleum oils were used for fungal and insect pests, whilst ammonium sulphate and sodium arsenate were used as herbicides.
The drawback for many of these products was their high rates of application, lack of selectivity and phytotoxicity 9. The growth in synthetic pesticides accelerated in the s with the discovery of the effects of DDT, BHC, aldrin, dieldrin, endrin, chlordane, parathion, captan and 2,4-D.
These products were effective and inexpensive with DDT being the most popular, because of its broad-spectrum activity 4 , DDT was widely used, appeared to have low toxicity to mammals, and reduced insect-born diseases, like malaria, yellow fever and typhus; consequently, in , Dr. Paul Muller won the Nobel Prize in Medicine for discovering its insecticidal properties. However, in resistance to DDT by house flies was reported and, because of its widespread use, there were reports of harm to non-target plants and animals and problems with residues 4, Throughout most of the s, consumers and most policy makers were not overly concerned about the potential health risks in using pesticides.
Food was cheaper because of the new chemical formulations and with the new pesticides there were no documented cases of people dying or being seriously hurt by their "normal" use There were some cases of harm from misuse of the chemicals.
0コメント