Rates of herbivory and defensive characteristics of young and mature leaves were measured for saplings of 46 canopy tree species in a lowland tropical rain forest (Barro Colorado Island, Panama). Grazing rates were determined in the field for sample periods in the early wet, late wet, and dry seasons. Leaf properties such as pubescence, toughness, water, protein, fiber, and phenolic contents explained over 70W% of the variation among plant species in the rates of herbivory on mature leaves. Leaf toughness was most highly correlated with levels of herbivory, followed by fiber content and nutritive value. Phenol content and phenol: protein ratios were not significantly correlated with damage. Mature leaves of gap-colonizing species were grazed six times more rapidly than leaves of shade- tolerant species. Gap-colonizers have less tough leaves, lower concentrations of fiber and phenolics, higher levels of nitrogen and water, shorter leaf lifetimes, and faster growth rates than do shade- tolerant species. Gap-colonizers did not escape discovery by herbivores to any greater extent than shade-tolerant species, as measured by the spatial distribution of plants or by the intraspecific dis- tribution of herbivore damage under natural or experimentally manipulated conditions. In 70W% of the species, young leaves suffered higher damage levels than mature leaves. Although young leaves are more nutritious and less tough and fibrous, they have two to three times the con- centrations of phenols. The temporal appearance of young leaves was not correlated with the distri- bution of herbivory among individuals of a species. Interspecific patterns of defense mechanisms are discussed in terms of current theories of plant apparency, and an alternative model for the evolution of plant defenses is presented.

Herbivory and defensive characteristics of tree species in a lowland tropical forest

▪ Abstract This review examines potential impacts of transgenic cultivars on insect population dynamics and evolution. Experience with classically bred, insecticidal cultivars has demonstrated that a solid understanding of both the target insect's ecology and the cultivar's performance under varied field conditions will be essential for predicting area-wide effects of transgenic cultivars on pest and natural enemy dynamics. This experience has also demonstrated the evolutionary capacity of pests for adaptive response to insecticidal traits in crops. Biochemical and genetic studies of insect adaptation to the Bacillus thuringiensis (Bt) toxins expressed by currently marketed transgenic cultivars indicate a high risk for rapid adaptation if these cultivars are misused. Theoretical and practical issues involved in implementing strategies to delay pest adaptation to insecticidal cultivars are reviewed. Emphasis is placed on examining the “high dose”/refuge strategy that has become the goal of industry and reg...

Sustainability of Transgenic Insecticidal Cultivars: Integrating Pest Genetics and Ecology

Compensatory growth in plants subjected to herbivory may alleviate the potential deleterious effects of tissue damage, whether to vegetative or reproductive organs Tissue destruction is rarely, if ever, translated monotonically into a proportional reduction of final yield Internal mechanisms of compensation involve modifications of plant metabolism; external mechanisms of compensation involve modifications of the plant environment that are favorable to plant growth and yield

https://www.jstor.org/stable/info/3544305

Compensatory plant growth as a response to herbivory

It has previously been postulated that when plants are stressed by certain changes in patterns of weather they become a better source of food for invertebrate herbivores because this stress causes an increase in the amount of nitrogen available in their tissues for young herbivores feeding on them. And this may cause outbreaks of such phytophagous invertebrates. Evidence is now presented that a similar physiological mechanism appears to operate when a wide variety of apparently unrelated environmental factors impinge on plants or parts of plants in such a way as to perturb their metabolism. A broken branch, lightning strike, fire, nutrient deficiencies or an otherwise adverse site; all may have this effect. With the advent of modern man the available agencies increase and diversify to include pesticides, irradiation and air pollutants. One common metabolic response by plants to all such agents impinging on them seems to be equivalent to that found in senescing plant tissues — the breakdown and mobilization of nitrogen in soluble form away from the senescing/stressed tissues. Young herbivores which chance to feed on such stressed/senescing tissues have a greater and more readily available supply of nitrogen in their food than they would have had if feeding on unstressed plants. As a result many more of them survive, and there is an increase in abundance of their kind. Such increases may be quite localised and short-lived or more widespread and persistent, depending on the extent and duration of the stress experienced by the plants. And in the face of this improved nutrition and survival of the very young, predators and parasites seem to have only a minor influence on subsequent changes in abundance of their herbivorous prey. Another effect of increased mobilization of nitrogen in stressed plants is an increase in the quantity of the seed that they set. This has led to the conclusion that increased abundance of some species of birds at such times is due to a greater supply of seeds as winter food for recent fledglings. But it may be that the increased abundance is due to the synchronous increase in phytophagous insects providing a richer source of protein food for laying hens and growing nestlings.

https://www.jstor.org/stable/info/4217356

The abundance of invertebrate herbivores in relation to the availability of nitrogen in stressed food plants.

Chemical and biological control are regarded as two main methods of suppressing insects
 and spider mites. These two methods are often thought of as alternatives in pest control.
 This is not necessarily so, for with adequate knowledge they can be made to augment
 one another.
 Biological control is part of the permanent natural control of population density.
 Chemical controls involve only immediate and temporary decimation of localized populations
 and do not contribute to natural control. Natural control may keep a pest species
 from ever reaching the economic-injury level or it may permit economic outbreaks.
 The frequency of these pest outbreaks varies from a regular to an occasional occurrence
 depending upon the level of the general equilibrium position in relation to the economic
 injury level and the types of fluctuations about the general equilibrium position.
 Integrated control combines and integrates biological and chemical controls. Chemical
 control is used as necessary and in a manner which is least disruptive to biological
 control. Integrated control may make use of naturally occurring biological control
 as well as modified or introduced biological control. Thought must be given to the
 biological control of not only the primary pest under consideration but also other
 potential pests.
 Integrated control is most successful when sound economic thresholds have been established,
 rapid sampling methods have been devised, and selective insecticides are available.
 In some situations, the development of integrated control requires the augmentation
 of biological control through the introduction of additional natural enemies or modification
 of the environment.
 Integrated control of the spotted alfalfa aphid has been achieved in California. Economic
 thresholds were established so that insecticides are applied only when damage is imminent.
 Native predators, introduced parasites, and entomogenous fungi now keep the spotted-alfalfa-aphid
 populations below the economic threshold for most of the year. When population counts
 in the individual field clearly demonstrate that a field is threatened, Systox is
 applied at low dosages. These chemical treatments give adequate control, but do not necessarily eradicate the aphids. Most of the predators
 and parasites survive and persist on the remaining aphids.

/pdf/the-integration-of-chemical-and-biological-control-of-the-pcl1r74huk.pdf

The integration of chemical and biological control of the spotted alfalfa aphid: The integrated control concept

Taxonomy of Vascular Plants George H. M. Lawrence COMPREHENSIVE source of information on theory, principles, & operating procedures in plant taxonomy plus an accounting of all families of plants of North America. Technical description of each family. $7.95 Parasitism & Symbiosis Maurice Caullery DEALS with parasitism from point of view of general biology. Makes clear that parasitism, commensalism, and symbiosis are different aspects of same general law. $5.50

Insect resistance in crop plants.

Resistance of Plants to Insects

Visual classifications were used successfully to measure differences in damage to com seedlings by the fall armyworm, Spodoptera frugiperda (J. E. Smith). Finer levels of damage are detectable using an 11-class rating system. If high levels of resistance occur, they can be detected visually. Use of seedlings permits more lines to be screened in less time with smaller space requirements than formerly, and tests can be conducted throughout the year.

FAW #1, a selection from Antigua 2D × (B10 × B14), and Texas Experimental Hybrid 6417 are the most resistant lines of corn studied thus far. Ioana sweet corn was used as the susceptible check.

Reginald H. Painter

Papers

Insect resistance in crop plants.

Resistance of Plants to Insects

Detecting Corn Seedling Differences in the Greenhouse by Visual Classification of Damage by the Fall Armyworm

The Economic Value and Biologic Significance of Insect Resistance in Plants

Differential Reactions of Two Biotypes of the Corn Leaf Aphid to Resistant and Susceptible Varieties, Hybrids and Selections of Sorghums