Insects And Humans

occur. This strategy allows for both immediate control and the build up of the control agent 755

complex for control throughout the crop growing season. Seasonal inoculation is especially useful in greenhouse operations where the crop, plus pests and natural enemies, are removed at the end of each growing season (van Lenteren, 2003). As of 2000, more than 125 control agents (including insects, mites, nematodes, and microorganisms) were being produced commercially, with a value of about US$50 million. In addition, biocontrol agents are produced and sold by many state- or farmer-supported organizations (van Lenteren, 2003).

The first known example of classical biological control occurred in the 18th century, when mynah birds imported from India were successfully used in the control of red locusts (Nomadacris septemfasciata) in Mauritius. However, full appreciation of the potential that insect parasitoids and predators might have as control agents developed only in the middle of the 19th century, following careful studies of the biology of such insects in the early 1800s. During the latter half of the 19th century, many well-known entomologists, both in Europe and North America, studied biological control and extolled its virtues, though these were largely unheeded until cottony-cushion scale was spectacularly controlled by the vedalia beetle in 1888-1889 (for this and other examples, see Section 2.3). In the late 1800s, based on studies of insect-diseases (especially those of the silkworm), several authorities, including Pasteur and Auduoin (France), Bassi (Italy), Metschnikoff (Russia), and Le Conte (United States), suggested that microorganisms might be used in the control of pest species (DeBach and Rosen, 1991; Federici, in Bellows and Fisher, 1999). However, for reasons outlined below, the widespread use of microorganisms for biological control did not materialize for almost a further 100 years (Section 4.3.1).

The theory behind the "new associations" approach, including neoclassical control, is that the pest has not coevolved with the biocontrol agent and therefore the former will not have an effective defense against the latter. In other words, neoclassical control should result in a higher success rate compared to classical biological control. Analysis of some 600 cases of biological control using exotic agents led Hokkanen and Pimentel (1989) to conclude that the success rate for new associations was about twice that of classical control (though in both situations there were a significant number of failures).

Biological control, when successful, generally has several advantages over control by insecticides. First, it is persistent; that is, once a control agent is established, it will exert a continuing influence on the population density of the pest. (Augmentative biocontrol agents are exceptions to this generalization and must be reapplied in the manner of chemical insecticides.) Second, in part related to its persistence, biological control is cheap because one application of the control agent is usually sufficient. Furthermore, the control agent is "ready-made"—it does not have to go through an extended and costly phase of research and development, though determination of the most suitable control agent(s) may take some time. As an example of the cheapness of biological control, DeBach and Rosen (1991) noted that the cottony-cushion scale project in 1888-1890 cost less than US$5000, yet it has saved the California citrus-fruit industry millions of dollars each year since. Because of escalating costs of insecticides, biological control may be the only (or principal) method of pest control in underdeveloped countries. Third, biological control does not endanger humans or wildlife through pollution of the environment.

A fourth advantage that has been claimed for biological control is its specificity toward the pest, though there are now known to be some major exceptions to this statement in the areas of classical and neoclassical biological control of both weeds and insect pests. These projects suffered from insufficient assessment of the risks associated with release of the biocontrol agent, in particular, failure to carry out sufficiently broad host-specificity

Beekeeping for Beginners

Beekeeping for Beginners

The information in this book is useful to anyone wanting to start beekeeping as a hobby or a business. It was written for beginners. Those who have never looked into beekeeping, may not understand the meaning of the terminology used by people in the industry. We have tried to overcome the problem by giving explanations. We want you to be able to use this book as a guide in to beekeeping.

Get My Free Ebook

Post a comment