Thomas S. Bellows

Population Processes and Dynamics of Laboratory Populations of Callosobruchus Spp

The results of single- and mixed- species studies are reviewed and the processes principally significant in forming the dynamics of these populations are discussed. The first of these processes is adult competition for oviposition sites, which is mediated by both exploitative and interference competition, and occurs both intraspecifically and interspecifically. Larval competition, apparently exploitative in nature, can produce very different outcomes in different populations, varying from nearly contest competition to scramble competition. The combinations of these processes result in different dynamics in different populations, varying from stable populations to those exhibiting cyclic behavior.

Biology of Arthropod Parasitoids and Predators

Basic knowledge of natural enemy biology and ecology is the foundation upon which the applications of biological control rest. In this chapter, aspects of the biology and ecology of arthropod parasitoids and predators are considered. The biology of vertebrates used in biological control is not covered. Following chapters cover the biologies of microbial pathogens and nematodes (Chapter 16) and weed control agents (Chapter 17).

Natural Enemy Conservation

Agricultural cropping systems consist of patterns of crops and sets of commonly used practices, and these define the conditions under which natural enemies encounter their hosts in these systems. The details of these practices interact with the biologies and needs of natural enemies in many ways. The goal of conservation as a form of biological control is to enhance conditions for natural enemy survival and reproduction relative to pests so that pest population growth rates are lowered and pest densities reduced over time.

Augmentation of Parasitoids, Predators, and Beneficial Herbivores

When natural enemies are absent, occur too late, or in numbers too small to provide effective pest control, releases may be made of reared natural enemies. This process is called augmentation and may be conducted either as a private commercial business or a government-provided service. Augmentation of natural enemies is practical in circumstances where permanent colonization of suitably adapted natural enemies is not feasible, for example, in protected culture or where existing natural enemies are not sufficiently effective. In the latter case, it may be appropriate to secure new species or strains of natural enemies from the pest’s homeland and permanently colonize these species. However, where such efforts are not productive in resolving the pest problem, augmentative liberations of natural enemies may be undertaken to supplement the action of existing natural enemies. A spectrum exists from releases which are meant only to inoculate the crop with the natural enemy (with most control being provided later by offspring of released organisms), termed inoculative augmentation, to those releases in which all control is expected to be exerted by the released organisms themselves, with little or no contribution by their offspring, a procedure termed inundative augmentation. Both large organisms such as hymenopteran and dipteran parasitoids, predacious arthropods, and herbivorous arthropods and small organisms such as plant or arthropod pathogens, plant disease antagonists, and arthropod-attacking nematodes can be augmented. In this chapter, we consider the augmentation of large organisms. In Chapter 11 we discuss the augmentation of small organisms.

Natural Enemy Monitoring and Evaluation

Evaluation is a basic part of all biological control work. Evaluation serves two broad purposes. First, it is the tool through which scientists obtain the biological information needed to separate effective biological control agents or methods from ineffective ones, so that further efforts can be focused on the most effective options. Evaluation methodology is especially critical when biological control is only partially effective, or when the biological effects of several partially effective methods or agents need to be compared. In such cases, the effect of the natural enemy may not be as dramatic as agents (or practices) that provide complete control of the pest. Second, economic evaluations of biological control projects are needed to provide economic planners with data on value returned for funds invested so that further investments can be made in activities with greatest likelihood of productive results.

Pest Origins, Pesticides, and the History of Biological Control

The human population is large and still expanding. To gain more farmland, native ecosystems are being rapidly converted to human use, destroying forests, soil, and native plants and animals. To produce sufficient food, commercial and subsistence farming systems must be highly productive, but sustainable and nonpolluting. However, to preserve the world for the future, space must be left for wild animals and wild places. To do both of these things is the great challenge of the early twenty-first century. Part of the solution to this problem is biological control, the foundation on which sustainable, nonpolluting pest control for tomorrow’s farms must be built.

Biological Control Agents for Plant Pathogens

Biological control of plant pathogens is fundamentally a matter of ecological management of a community of organisms, as is all biological control. In the case of plant pathogens, however, there are two distinctions from biological control of organisms such as insects and plants. First, the ecological management occurs at the microbial level, typically in microcosms of the ecosystem such as leaf and root surfaces (Andrews 1992). Second, biological control agents include competitors, as well as parasites. While hyperparasites of plant pathogens and natural enemies of nematodes function in much the same way as do natural enemies (parasitoids) in arthropod systems (by destroying the pest organisms), competitors function by occupying and using resources in a nonpathogenic manner and in so doing exclude pathogenic organisms from colonizing plant tissues. Microbes which negatively affect pathogenic organisms are referred to as antagonists.

Methods for Biological Control of Plant Pathogens

Organisms for biological control of plant disease can be used in various ways, but most attention has been given to their conservation and augmentation in a particular environment, rather than to the importation and addition of new species as is often done for insect or weed control. The choice of these approaches is in part because there is usually a diverse set of microbes already associated with plants. These microbes provide substantial opportunity for development of resident species as competitors or antagonists to pathogenic organisms.

Augmentation of Pathogens and Nematodes

Numerous species of nematodes and microorganisms have potential for use as commercial products (Starnes et al. 1993). Successful commercial development of pathogens for augmentative biological control involves: agent selection (to obtain the best species and strains for the target pest); development of cost-effective methods for mass rearing; effective methods for storage and shipping of the agent; creation of formulations to protect and deliver the agent to the target pest’s location; field testing of the product’s efficacy and methods for its application; economic factors affecting product development and markets; and demonstration of safety of products to man and the environment.

Pathogens and Nematodes of Arthropods and Pathogens of Vertebrates

More than 1500 species of pathogens are known to attack arthropods (Miller et al. 1983). These include bacteria, viruses, fungi, protozoa, and nematodes. Historical developments in the recognition and understanding of pathogens of arthropods are summarized by Steinhaus (1956) and are briefly reviewed in Chapter 1. Detailed treatment of the taxonomy and biology of arthropod pathogens is given by Tanada and Kaya (1993) and, for nematodes, Kaya (1993). Much of the research on these pathogens is directed at development of methods for their culture, mass production, formulation, and use through augmentation as biological pesticides (see Chapter 11).