Ntx

760 active only in certain environmental conditions. Added to these problems were technical difficulties that hampered research in this area, especially the inability to mass-produce microorganisms on a year-round basis for laboratory study as well as field trials. This has been mainly overcome through the use of artificial insect diets and tissue culture, though these methods are not, by and large, satisfactory for large-scale commercial production because of their labor-intensive nature and high costs. Another major technical problem that required solution was the development of suitable protectants against ultraviolet light to which most microorganisms are especially sensitive. Oddly, it was one of their disadvantages, namely, poor viability outside their host (hence the need to reapply them, much like chemical insecticides), that spurred industry into research and, ultimately, development of a number of commercial preparations. Their advantages include safety to humans and wildlife compared to conventional insecticides, specificity (and, therefore, safety to beneficial insects), biodegradability, and lower registration costs (Laird et al., 1990; Roberts et al., in Pimentel, 1991, Vol. 2; Federici, in Bellows and Fisher, 1999; Flexner and Belnavis, in Rechcigl and Rechcigl, 2000; Khetan, 2001; Koul and Dhaliwal, 2002).

Not surprisingly, in view of the diversity of both pests and their pathogens, there are many methods for regulating insect populations with microorganisms though Harper (1987) and Fuxa (1987) cited three general approaches: introduction, augmentation, and conservation. In the first approach, introduction of the pathogens into the pest's ecosystem may be inoculative or inundative. Following inoculative introduction (colonization), the pathogen exerts more or less permanent regulation of the pest population; in other words, this is a form of classical biological control. Good examples of introduced pathogens that work in this way are: (a) Bacillus popilliae and B. lentimorbus, which cause milky disease in the Japanese beetle, Popillia japonica, an important pest of lawn and other grasses in the United States; (b) a nucleopolyhedrovirus, accidentally introduced into Canada in the early 1940s, that has kept populations of the European spruce sawfly (Gilpinia hercyniae) below the economic threshold level since the initial epizootic; (c) a nucleopolyhedrovirus that exerts good control over the European pine sawfly (Neodiprion sertifer) in Canada; and (d) the nematode Deladenus siricidicola, released in Australia in 1970 for control of an introduced European woodwasp Sirex noctilio.

Inundative introductions are those in which an exotic pathogen exerts relatively rapid, but temporary, suppression of the pest population. In other words there is no recycling of the pathogen in the pest's ecosystem and reapplication of the pathogen is necessary if further control is required. Thus, this form of microbial control is analogous to control with a conventional chemical insecticide. The use of Bacillus thuringiensis for control of lepidopterous and coleopterous pests and mosquitoes is a prime example of inundative introduction.

Augmentation is the placing of additional amounts of a naturally occurring pathogen into the ecosystem to increase disease prevalence. As Harper (1987) noted, this is useful when natural epizootics are asynchronous with pest outbreaks or when the incidence of disease is too low to be economically valuable. In fact, many of the currently registered en-tomopathogens (see below) are utilized in this way, for example, the nucleopolyhedroviruses used to control Heliothis spp. on cotton, Orgyia pseudotsuga (Douglas fir tussock moth), and Lymantria dispar (gypsy moth), the microsporidian Nosema locustae against rangeland grasshoppers, and the fungus Hirsutella thompsonii against the citrus rust mite (Phyllocop-truta oleivora).

Conservation refers to the enhancement of naturally occurring microbial pest regulation as part of an overall pest management strategy. It may include, for example, choosing a fungicide against a plant disease that has least impact on the pest entomopathogen, reducing the amount of chemical pesticide applied so that host pest populations do not fall below

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