One company engineers the expression of toxins into a bacterium with a thick cell wall, so that the proteins are protected from sunlight. Another method is to have the toxins expressed by plants.
This method is controversial, as it may cause such intensive selective pressure that pests may rapidly develop resistance to Bt. Applying Bt products with ultrafine oil may prolong the toxin residues, and the oil itself can be toxic to the target pest. Organophosphate and carbamate insecticides act through a common mechanism. Both classes of insecticides bind to acetylcholinesterase, an enzyme needed for the normal rapid removal of acetylcholine from the nerve synapse.
When acetylcholine is not removed from the synapse, nerve fibers send multiple trains of signals. As a group, organophosphates and carbamates vary tremendously in their toxicity to humans, however, following repeated exposure from misuse, even the safest of these insecticides can cause human poisoning. Among organophosphates, malathion has been widely and effectively used by homeowners for controlling many insects.
Its toxicity to humans is very low, and its residues disappear from plants relatively rapidly. It is a contact insecticide, meaning that the chemical stays on the surface of the plant and affects insects through contact or ingestion.
It is well adapted for use in both vegetable and flower gardens. Acephate is an organophosphate especially useful for controlling sucking insects on ornamental plants because it is a systemic, meaning that the active ingredient is absorbed into the plant tissues and sap, where it may be consumed by sap feeders. It has a relatively short residual, and is also useful for control of chewing insects. Chlorpyrifos is an organophosphate with greater mammalian toxicity than malathion or acephate. The special properties of chlorpyrifos that make it useful are its longer residual toxicity.
This makes it particularly useful on ornamental plants when control is needed for an extended period, for example, against bark borer adults and scale crawlers. Carbaryl is a carbamate insecticide. With low relative toxicity to humans, Carbaryl is widely used by homeowners on certain vegetables, fruits, and ornamentals. It has been implicated in killing honeybees when inappropriately applied to open blossoms and is also highly toxic to earthworms, predatory mites, insect predators and parasites.
Horticultural oils used for controlling insects and mites and for suppressing some plant diseases vary considerably in their potential to cause injury to plants. They are very useful in killing scales, aphids, and mites. These oils work by coating the respiratory apparatus of target pests, thus causing their suffocation.
Dormant oil sprays, particularly the "superior" type, may be used on dormant deciduous trees and shrubs. True dormant oils are most effective when applied in the early spring after the danger of freezing weather and before buds swell. A more highly refined grade of oil is called "ultrafine oil. Ultrafine oils may be used on a great variety of plants, including conifers, and on foliage during the growing season.
The waxes on Colorado blue or Koster spruces are permanently darkened following oil applications, so if the natural color of the foliage is important, oil should not be applied to these species. Agitation of the spray mixture is extremely important to maintain an emulsion. Thorough coverage is essential when using oil, because it only acts after coating the insect or mite. Commercially labeled insecticidal soap is a potassium salt of a fatty acid, and is little different from liquid dishwashing detergent, except that the insecticide product is chemically purer.
For the same reason that the purer ultrafine oils are safer for use on plants than dormant oil, commercial insecticidal soap is also safer for plant treatments. The product has been optimized for insecticidal action, while limiting the potential to cause plant injury.
Insecticidal soaps appear to principally work by allowing a film of water to coat the respiratory apparatus of targeted aphids, mites, or soft-bodied insects.
When this occurs, the insect or mite drowns. Once the residue has dried, soap becomes non-toxic to insects and mites. Soaps may also enter the body of the insect, disrupting cell membranes in the process. Soaps are especially useful for control of aphids. The ability to control any pest with soap depends on thorough coverage with the spray. Soap solutions also interact with the waxes on plant leaves to determine how well they work to control spider mites. Spider mites on very waxy leaf surfaces are much more difficult to kill with soap than those on leaves that are easily wetted.
Imidacloprid is the first chloronicotinyl insecticide to gain registration. It has a mode of action for insects related to that of nicotine, however, unlike the natural product, it has very low toxicity to mammals. It binds to the nicotinic acetylcholine receptor in the nerve synapse, and consequently disrupts nerve transmission in insects by causing uncontrolled firing of nerves. Imidacloprid has a short residual life when exposed to the sun on leaf surfaces, thereby limiting its usefulness in foliar sprays.
However, it has a long residual days or more when protected from the sun in the soil. It is readily taken up by the roots of plants, and usually provides at least one season of control for aphids, adelgids, soft scales, whiteflies, lace bugs and plant bugs in ornamental plants.
Treatments of trees, shrubs, and flowers, require a wettable powder formulation labeled for these uses. One management strategy is to treat in the early spring, then not treat again until the pest reappears which can be two or more years later.
It has low toxicity to earthworms, and because it is a systemic and is contained within plant tissues, it is probably non-toxic to beneficial mites and insects visiting leaf surfaces of systemically treated plants. Imidacloprid is highly effective against white grub larvae in turf, and is applied at a fraction of the amount of active ingredient compared to other insecticides.
Granular products specifically labeled for control of white grubs in lawns do not have claims on their labels for control of sucking pests on adjacent trees and shrubs. However, the homeowner should anticipate some benefit to these plants because they may take up the active ingredient through roots overlapping turf areas.
Many insecticides registered for use on landscape ornamentals are not available to homeowners because their sale is restricted to licensed pesticide applicators. These products are not listed in the remainder of this publication, but some of them have properties that are important to consider if the work needs to be done by a professional.
Register for a free account to start saving and receiving special member only perks. Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book.
It should be taken into account in breeding programs aimed at improving the quality or yield of agricultural crops or livestock and in introducing known crop varie- ties or animal breeds into new geographic areas. Exploitation of resistance to its full potential involves a broad interdisciplinary approach. With a few con- spicuous exceptions, consideration has not been given to host resistance in past entomological research.
In recent years there has been some increase in studies of insect resistance in plants, both in respect to the number of plants and insects investigated and to the depth of the studies. There have also been improvements in knowledge of insect physiology and behavior, together with means of studying the mi- nute quantities of various substances that are probably the basis of resistance.
For these reasons, some of today's concepts about resistance may soon re- quire modification or replacement. Breeds or lines of cattle, sheep, hogs, and horses possess different degrees of resistance to arthropod attack. This dif- ference in resistance among animals is present from birth to old age and does not depend on previous exposure to the pests.
This was true even before the widespread use of DDT and other organic in- For example, the satisfactory control of the Colorado potato beetle, Leptinotarsa decemlineata Say , obtained with the early arsenicals, apparently made any real, detailed study of the biology of this insect in the United States less necessary, particularly the relation of the insect to its hosts.
In no respect has the study or use of resistance to arthropod pests in do- mestic animals advanced as far as with domesticated plants. This is partly be- cause of the negligible cost of plants compared with animals, the far shorter time usually required for a generation in plants, and because of greater oppo- sition to hybridization between animal breeds compared with the crossing of plant varieties.
In many instances, the findings in studies of resistance to in- sects, mites, and ticks in animals are similar to principles developed in studies of insect resistance in plants.
Most differences are related to mobility of ani- mals, the presence of a blood system and immune reactions, and complexities introduced by the wider role of hormones in animals. The first instances of the use of plant resistance to insects are as old as the earliest work in applied entomology. The earliest record of a recognizable insect-resistant variety is the Winter Majetin variety of the apple, Malus pumila Miller, which was reported resistant to the woolly apple aphid, Eriosonw lanig- erum Hausmann , in and is still resistant at the latest report.
Within a few years after the introduction of the Hessian fly,Mayetio! All trace of some of the first varieties reported as resistant to the Hessian fly has apparently been lost, but, in a few cases, selections of wheat bearing the same names were later found to be resistant.
In it was reported that there was a great difference in susceptibility to grasshoppers, Melanoplus spp. The corn was much more susceptible than the sorghums. Since then, this difference has been seen repeatedly during each grasshopper outbreak in areas in North America where these crops are grown.
This is true for all species of grasshoppers that have been observed in outbreak numbers in the area, despite the fact that, during the intervening years to the present, the resistant sorghums have increased from a few thou- sand acres to many millions, and grasshoppers have not yet "learned" to eat the sorghums. About the middle of the nineteenth century, it was found that some of the American species of grapes, Vitis spp.
This knowledge made possible the grafting of European grapevines onto phylloxera-resistant rootstocks from the United States and formed the basis for a method of control that is still most important. These examples, which are about a century old, and as old as or older than any other insect-control method, emphasize the relative permanence of resistance. Left: Kansas hybrid Right: U.
Resistance to grass- hoppers occurs more commonly in corn inbreds derived from varieties formerly grown in the western United States, where grasshoppers have long been a feature of the en- vironment, than from those in more eastern parts of the country. Courtesy of Kansas Agricultural Experiment Station The first extensive search for sources of plant resistance to insects was made in California over a period of 10 years, beginning in Seeds of over a hundred varieties of small grains, especially wheat, were obtained, and plants grown from these seeds were exposed to infestation by the Hessian fly.
The results were recorded, but nothing further was done for several decades, when. Possibly the earliest studies of the inheritance of pest resistance were in and and involved the resistance of cotton, Gos- sypium spp. Field and, later, greenhouse studies of Hessian fly resistance in wheat were begun by the Kansas Agricultural Experiment Sta- tion in , and have since continued without interruption. These studies led to the distribution in Kansas of the Hessian fly-resistant wheat selection Kawvale in and in following years to the distribution of nine wheat varieties de- rived from hybrids and resistant to the insect.
There are excellent examples of the successful use of resistant crop varieties for control of infestation and damage caused by various insects.
Six varieties of wheat, resistant to the wheat stem sawfly, Cephus cinctus Norton, are being grown on several million acres in Canada and in Montana, North Dakota, and neighboring states, where wheat sometimes could not previously be produced because of this insect, for which no other economic control measure is avail- able.
The availability of cotton varieties resistant to the leafhopper Empoasca fascialis Jack in South Africa has made the growing of cotton possible where it could not be grown economically before the advent of DDT, and without resistant varieties. Hessian fly-resistant varieties of winter wheat, satisfactory in milling and baking qualities, with high yield, and disease-resistant are avail- able in all the major wheat-growing areas of the United States.
More than 20 such fly-resistant wheat varieties are presently recommended by the agricul- tural experiment stations of the states involved. For the first time a high level of Hessian fly control is available to all wheat-growing farmers at no cost except, perhaps, a small amount for superior seed Figure 3. Breeds of animals with demonstrated resistance to arthropod attack have been recognized in recent times only, but reported differences date back much further.
An Arabic report of the Crusades indicates that Arabian horses were less bothered by Hippobosca ssp. Native tribes of West Africa claim that West African small-humped cattle are more resistant to the attacks of tsetse flies Glossina spp. Definite attempts to develop arthropod resistance in domestic animals are difficult to trace. Early in the twentieth century, efforts were made in South Africa to combine the freedom from insects and ticks shown by the Afrikander cattle with the more desirable qualities of European breeds.
Results were not gratifying. These efforts led to the establish- ment of several breeds that are less adversely affected by biting flies than the. Wheat planted September 6, Left to right: Kaw, tolerant; Bison, susceptible; Ottawa, resistant with stake ; Tenmarq, susceptible with stake ; Ponca, resistant; Pawnee, resistant.
Tolerant wheats have nearly as many insects at the base as susceptible ones but are less injured. On resistant wheat varieties, few or no flies develop, even though the plants receive just as many eggs as the susceptible or tolerant varieties.
Some of the best known lines of purebred Here- fords have been selected on a basis of light-colored hair coat, because these strains are less susceptible to the horn fly, Haematobia irritans Linnaeus. Australian sheep ranchers have found that English breeds of sheep are far less susceptible to attack by wool maggots larvae of several Calliphoridae than are the Spanish-developed Merino breed.
Crosses between the breeds show intermediate resistance. The term "resistance" is used for beginning studies in the field or in the green- house when one does not know what components are involved. Most such cases of resistance are made up of varying degrees of one or more components: nonpreference and preference, antibiosis, and tolerance. These components appear to be generally comparable in plants and animals. Nonpreference and. Anti- biosis refers to the adverse effects on the insect mortality, size, and life history that result from pests feeding on a resistant host.
Tolerance refers to a basis of resistance in which the host shows an ability to grow or reproduce or repair injury while supporting a population approximately equal to that damaging a susceptible host. Each of these components is controlled by one or more genetic factors. Therefore, higher or more stable levels of resistance may often be ob- tained by combining components of resistance from several sources or by com- bining genetic factors for each of the three components.
Analyses of the com- ponent or components of resistance present are needed early in the research, first as a prelude to a separate study of the basis of resistance of each compo- nent, and, second, before a separate study of the genetics of each component of resistance is initiated. Only one case is known where two components of resistance are governed by a single genetic factor, the H3 gene for Hessian fly resistance in wheat.
The chemical resistance factor, 6-methoxybenzoxazolinone RFA , the genetics of which is unknown, is found in corn leaves of inbreds re- sistant to the European corn borer, Ostrinia nubilalis Hiibner. It acts as a feeding deterrent as well as a growth inhibitor; hence, it could be classified both as a nonpreference and an antibiotic component.
Some research workers on insect resistance would confine the term resis- tance to what is here designated as the component antibiosis.
There are at least four reasons for using the term resistance for any combinations of one or more of the components just named. One example is the resistance to greenbugs, Schizaphis graminum Rondani , in wheat and barley, Hordewn vulgare Linnaeus Figure 4. It cannot be emphasized too often that the resistance as first seen in the field generally results from one or more components of resistance, each of which is a complex of interacting factors.
Increasingly, research. Reproduction of the aphid is twice as great on the suscep- tible as on the resistant variety, but the resistant variety carries a high level of tolerance. Compare with Figure 5. Courtesy Kansas Agricultural Experiment Station has demonstrated that inherent responses of insects to inherited constitutents or characteristics of plants are far more stable than previously supposed.
Thus, the value of the nonpreferred characteristics can rarely be estimated on the basis of present information. Insects May Starve Rather Than Feed on Resistant Plants There are at least two types of nonpreference: first, that which is manifest only in the presence of a preferred host; second, one that can be demonstrated as present in the resistant plant even in the absence of the preferred host.
In the latter type, the nonpreference may be so strong that the insect would starve to death, even though no untoward results would follow if it fed on the nonpre- ferred plant. This was clearly demonstrated by Waldenbauer's studies of the tobacco hornworm, Manduca sexta Johannson , where large intact larvae re- fused to feed on nonpreferred plants, but larvae with maxillae removed some- times ate the plants without ill effects.
In nature, the original choice or original response to the host after oviposition is made by first-instar larvae or nymphs, which may be more sensitive to the constituents of the host than larger larvae or nymphs. Therefore, it is very difficult to separate extreme nonpreference. In this research, the aphids were given a choice of samples of the same chemically defined diet illuminated by different colors.
The insects usually picked the food illuminated with yellow or orange light, and they reproduced abundantly. How- ever, when confined with the same food illuminated only with blue light, they did not feed sufficiently to live or reproduce. On food illuminated with red light, they gained very little and reproduction was poor. When similar artificial food was illuminated with green light, survival was about 50 percent, but weight gained by survivors was normal.
The females of some insects refuse to oviposit on nonpreferred hosts. Others will oviposit on a nonpreferred host near the preferred one but not on a non- preferred host some distance away. The work on the pink bollworm, Pectino- phora gossypiella Saunders , of cotton showed wide differences between ovi- FIGURE 5 Differential damage by spotted alfalfa aphid, Therioaphis maculate Buckton , in greenhouse to alfalfa varieties, Cody, resistant plants healthy , and Buffalo, susceptible plants killed.
Cody was derived from 22 spotted alfalfa aphid- resistant plants found in Buffalo alfalfa. The resistance of Cody is partially dependent on the tolerance component but is principally due to the fact that the aphid is unable to maintain a population on the variety long enough to kill many plants.
Compare with Figure 4. Courtesy Kansas Agricultural Experiment Station. The feeding and oviposition patterns in most insects are a complex series of responses to features of the environment and to characteristics of the host.
Presumably, the earliest insects found their hosts through random searching, and some still do. Many insects respond to such features of the environment as gravity, light, light-dark margins, and wind movement of a given level. These responses bring them within a range from which they can respond to a specific attribute of the host. Such responses may then take the form of either kineses or taxes. The former provide response to arrestants, the latter to attractants.
At first the taxes appear to come from a stimulus for biting or piercing but, later, from a stimulus to continue feeding. As applied to resistance, nonprefer- ence may take the form of one or more breaks in the chain of responses leading to feeding or oviposition. These breaks are the absence of an arrestant or attrac- tant, the presence of a repellent, or an unfavorable balance between arrestant or attractant or both on the one hand, and a repellent on the other.
Most of what is known of the bases of differences in relationships of insects to susceptible and resistant hosts comes from studies of insects on different host species. Less information is available on the bases of interactions between any insect and susceptible or resistant host varieties.
Presumably, the same information acquired by the study of differences between host species would apply to differences between resistant and susceptible varieties, but the latter area greatly needs detailed study.
The preference phenomena responded to by insects are extensive, including such physical characters as color, plant surface, internal structure of the plant, and reflection of infrared and other rays.
It is generally believed that chemical characteristics are the most important. An insect usually responds to only a few chemicals, and with unbelievable sensitivity when it does.
A single sensory hair of the black blow fly, Phormia regina Meigen , when touched by a sucrose concentra- tion of 3 one-millionths of a gram per cc of water will cause the blow fly to respond. There appear to be little data on the long-time persistence of various repellents. Materials extracted from resistant trees or parts of resistant trees have protected susceptible wood from the powder-post termite, Cryptotermes brevis Walker, for periods of 4 to 11 years.
The value of preference as a resistance mechanism has been questioned by various workers. In a few cases preference appears to be the only component of resistance. It is characteristic of a number of insects with chewing mouthparts where the first-instar larvae on resistant plants take only small nibbles. This is true of the Colorado potato beetle on wild potato, Solanum demissum Lindley. The repellent ma- terial is apparently demissine, which may also be toxic. Colonies of the insect cannot be maintained on this resistant species.
The same small feeding lesions are characteristic of other examples of resistance, including the resistance of some strains of corn to the European corn borer.
It is not always clear whether these reduced feedings are the result of extreme nonpreference, or some form of antibiosis, or both.
Horn flies are normally more prevalent on dark-colored areas of an animal than on lighter areas. Significant differences in the preference for dark over light hair coat by horn flies and stable flies have been demon- strated in Holstein, Ayreshire, and Hereford breeds of cattle when the animals are pastured together.
However, if light-colored animals are separated from darker animals, they may have large numbers of flies. Lines of Herefords less attractive to horn flies have been developed, but the ease with which these flies can now be controlled by other means has resulted in less emphasis on selecting for nonpreference by horn flies and more emphasis on conformation and effi- cient food utilization.
Skin thickness has long been suggested as a factor in preference or non- preference of stable flies, Stomoxys calcitrans Linnaeus , and horn flies occur- ring on Holstein, Ayreshire, Jersey, or Guernsey cattle. Significant correlations have been demonstrated with the first three breeds but not with the last. No significant differences in the numbers of house flies, Musca domestica Linnaeus, feeding on animals of different skin thickness were noted except when biting flies were numerous.
Then the house flies fed on drops of blood resulting from the feeding punctures of the biting flies, and the numbers of house flies were correlated with the activity of biting flies and hence indirectly with the skin thickness. The site of skin measurement was important, and measurements on the side of the bovine provided the best estimate of fly numbers, followed by the neck and escutcheon.
Irritability or nervousness of the host has been suggested as a factor in non- preference of stable flies and horn flies for individuals, and a high degree of cor- relation has been obtained between the number of flies feeding and the tendency of the animal to frighten the flies away.
The heritability of this factor is high but of questionable value in a breeding program. Nonpreference in ticks for breeds of cattle has been ascribed to several fac- tors, including shorter or thinner hair coat; thicker skin; wrinkled, loose-fitting skin; and differences in the secretions of the sebaceous glands.
Some of the tick. However, the nonpreference of mosquitoes and horse flies for zebu cattle has not been transferred successfully. Effect of Insect Pest-Plant Host Relationship: Insect-resistant crop varieties suppress insect pest abundance or elevate the damage tolerance level of the plants. In other words, insect-resistant plants alter the relationship an insect pest has with its plant host. How the relationship between the insect and plant is affected depends on the kind of resistance, e.
Antibiosis resistance affects the biology of the insect so pest abundance and subsequent damage is reduced compared to that which would have occurred if the insect was on a susceptible crop variety.
Antibiosis resistance often results in increased mortality or reduced longevity and reproduction of the insect. Antixenosis resistance affects the behavior of an insect pest and usually is expressed as non-preference of the insect for a resistant plant compared with a susceptible plant. Tolerance is resistance in which a plant is able to withstand or recover from damage caused by insect pest abundance equal to that damaging a plant without resistance characters susceptible.
Tolerance is a plant response to an insect pest. Thus, tolerance resistance differs from antibiosis and antixenosis resistance in how it affects the insect-plant relationship. Antibiosis and antixenosis resistance cause an insect response when the insect attempts to use the resistant plant for food, oviposition, or shelter. Advantages to the Use of Insect-Resistant Crop Varieties: Use of insect-resistant crop varieties is economically, ecologically, and environmentally advantageous.
Economic benefits occur because crop yields are saved from loss to insect pests and money is saved by not applying insecticides that would have been applied to susceptible varieties. In most cases, seed of insect-resistant cultivars costs no more, or little more, than for susceptible cultivars. Ecological and environmental benefits arise from increases in species diversity in the agroecosystem, in part because of reduced use of insecticides.
Increases in species diversity increase ecosystem stability which promotes a more sustainable system far less polluted and detrimental to natural resources. The IPM concept stresses the need to use multiple tactics to maintain insect pest abundance and damage below levels of economic significance. Thus, a major advantage to the use of insect-resistant crop varieties as a component of IPM arises from the ecological compatibility and compatibility with other direct control tactics.
Insect-resistant cultivars synergize the effects of natural, biological, and cultural insect pest-suppression tactics. The "built-in" protection of resistant plants from insect pests functions at a very basic level, disrupting the normal association of the insect pest with its host plant. The compatible, complementary role plant resistance to insect pests plays with other direct control tactics is, in theory and practice, in concert with the objectives of IPM.
All crop cultivars should contain resistance to insect pests. Plant resistance to insect pests has advantages over other direct control tactics.
For example, plant resistance to insects is compatible with insecticide use, while biological control is not. Plant resistance to insects is not density dependent, whereas biological control is. Plant resistance is specific, only affecting the target pest. Often effects of use of insect-resistant cultivars are cumulative over time.
Usually the effectiveness of resistant cultivars is long-lasting. The role of plant resistance to insects in IPM has been well defined, at least in theory. However, the specific role a resistant cultivar plays in a particular IPM situation is crucial to successful deployment of the resistant cultivar.
The impact of the resistant cultivar on standard cultural, biological, and insecticidal control methods should be well defined. Likewise, the impact of each of these control tactics on the resistant cultivar also must be defined.
Several definitions have been used to convey the relative level of resistance in a plant. The first step in resistance breeding programmes is the collection of natural variability followed by finding out the sources of resistance. The information on these aspects has been described in detail in Chap. The next step is to incorporate the resistance gene s from the donor parent s using various methods including induced mutations, where the susceptible alleles are altered by the use of mutagens.
These methods are discussed in this chapter. In view of the dynamic nature of parasites, the resistant gene s fall susceptible after a few years or are no longer effective.
0コメント