Pests, classification

Pesticide—General classification of chemicals specifically developed and produced for use in the control of agricultural and public health pests. 

Phytochemicals are biologically-active, non-nutritive secondary metabolites which provide plants with colour, flavour and natural toxicity to pests. The classification of this huge range of compounds is still a matter of debate, but they fall into three main groups ... 

The discovery that, in industrialised societies, diets deficient in fruits and vegetables can effectively double the risk of developing many different types of cancer has focused renewed attention on the beneficial properties of these foods (Block e/a/., 1992 Patterson ef a/., 1990 Southon and Faulks, 2002). As we have seen, plant foods are rich in micronutrients, but they also contain an immense variety of biologically active secondary metabolites providing colour, flavour and natural toxicity to pests and sometimes humans (Johnson et ah, 1994). The chemistry and classification of such substances is still a matter for much research and debate, but this has not prevented attempts to isolate and exploit substances that have variously been termed protective factors , phytoprotectants , phytochemicals and nutraceuticals . Phytochemical compounds include ... 

This comprehensive definition makes it elear that a wide number of substances may be eonsidered to be pestieides, and that the eommonality among all pestieides is their ability to provide eontrol over pests. A variety of classifications for pesticides have been developed that are specific for the type of pest controlled. Insecticides, for example, are pesticides that control insects, while herbicides control weeds and fungicides control plant diseases (molds). In addition to these major classifications of pesticides, there are many other classifications. These include nematicides (for nematode control), acaracides (mite control), rodenticides (rodent control), molluscicide (snail and slug control), algacides (algal control), bacteriocides (bacterial control), and defoliants (leaf control). 

The Importance of developing crop plants that are resistant to major Insect pests has created a need for detailed examination of the mechanisms Involved In resistance. The widely recognized classification proposed by Painter W appears to provide an acceptable break-down of the possible bases of resistance for most purposes. However, some modification of the terminology may be desirable before beginning to analyze the Individual mechanisms Involved. The term "nonpreference" refers to a behavioral response of the Insect to a plant, whereas "antibiosis" and "tolerance" refer to plant characteristics. This anomaly has been addressed by Kogan and Ortman ( ), who suggested the term "antlxenosls" to describe the plant properties responsible for nonpreference. 

Smith (24) conducted intensive studies of the factors involved in the use of oil sprays to control California red scale and other pests of citrus in southern California. He found that insecticidal efficiency and deleterious effect on the trees were closely related to the so-called weight of the spray oil, as indicated by the distillation range, and that this provided a better basis for classification of spray oils than viscosity. The relationship of the unsulfonated residue of petroleum oils to tree injury had been clearly established previ-... 

OPs have been in use for several decades as important chemicals for the control of crop pests. With their chemical and biochemical reactions, OPs have been well established as extremely poisonous chemicals. This classification is due to the inhibition of the marker enzyme ChE, which is produced in the liver. Blood enzymes provide an estimate of tissue enzyme activity. After acute exposure to OPs or a nerve agent, the erythrocyte enzyme activity most closely reflects the activity of the tissue enzyme. Once the OPs inhibit the tissue enzyme, it cannot hydrolyze ACh, and the accumulation stimulates the affected organ. Based on the manner of exposure (dose and duration) to different OPs, a series of toxicity signs and symptoms set in the organism, leading to death. These are important aspects to be closely monitored among pest control operators and occupational workers exposed to OPs. 

The last of these is the most common classification scheme and is based on the pest group controlled. 

TABLE 11.1 Classification of Pesticides According to Target Pest or Function... 

The term pesticide, as used here, is an all encompassing one that includes all chemicals deliberately and legally used to prevent, destroy, repel, or mitigate any pest, that is, any unwanted, living species. Different subdivisions of pesticides, however, target different types of species. The following classifications list the chemical pesticide subdivisions and the species they target, t1 ... 

The new Directive describes biocides as chemical preparations containing one or more active substances that are intended to control harmful organisms by either chemical or biological, but by implication, not physical means. The classification of biocides is broken down into four main groups — disinfectants and general biocides, preservatives, pest control and other biocides and these are further broken down into 23 separate categories. 

Pesticides can be classified in several ways. The clearest and most widely used classification is based on the practical purpose of application. Thus, pesticides are classified as microbicides against microbial pests, zoocides against animal pests and herbicides against weeds. 

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