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756 studies (Louda et al., 2003; Sheppard et al., 2003). For example, Cactoblastic cactorum, introduced so successfully into Australia for control of exotic Opuntia species (Section 2.3), was released on the Caribbean island of Nevis in 1957 as a control agent for native weedy Opuntia. However, it was soon found on some of the rarer (non-weedy) Opuntia species, whose numbers have been significantly reduced. Further, the moth has now spread throughout the Caribbean, both naturally and by introductions, and has reached Florida, where it is threatening some of the native Opuntia species, including some that are endangered (McFadyen, 1998). The tachinid fly Compsilura concinnata was introduced into North America in 1906 as a control agent for the gypsy moth (Lymantria dispar) and the brown-tail moth (Euproctis chrysorrhea). Despite the knowledge that the fly is multivoltine (whereas the moths are univoltine) and would therefore use non-target species to complete its annual cycle, releases were continued until the mid-1980s. Surveys have shown that the fly attacks >200 species of Lepidoptera and Hymenoptera, including giant silkworms (Saturniidae), some of which are now endangered or extirpated in some states (Louda et al., 2003).

Two other advantages that have been suggested in the past are now debatable, namely, that biological control does not stimulate "genetic counterattack" by the pests and that it does not result in the growth to pest status of species that are economically unimportant (Huffaker, 1971; Howarth, 1991).

If biological control offers so many advantages over insecticides, why has it, in most instances, come only a distant second to these compounds in terms of usage? What are its disadvantages? Perhaps the main one is psychological because users like to see immediate results (profits?) for their efforts. In biological control it may take some time (even years) for a control agent to subdue a pest, by which time a user's patience (and profit margin) have worn thin, especially under the considerable and continuous advertising pressure of insecticide producers. Further, the new equilibrium density that a pest attains when controlled biologically is almost certainly higher than the density immediately after insecticide treatment, which again may be unsatisfactory as far as a user is concerned, especially if the crop being grown is of high unit value, for example, fresh fruit. Consumers, too, are involved here, as they have become accustomed to "blemish-free" produce and may not buy even slightly damaged material. Other disadvantages have appeared after the introduction of biological control agents, including extinction of non-target species, enhancement of target pest populations as a result of secondary outbreaks, development of new pests, and effects on human health. A widely accepted tenet of ecological predator-prey theory is that the predator (i.e., biological control agent) cannot cause the extinction of its prey (i.e., pest). However, Howarth (1991) provided numerous examples of both target and non-target animals (including many insects) that have become extinct as a result of the direct or indirect effects of biological control agents. In other situations, introduction of an exotic control agent has led to displacement of already present natural agents, without significant gains in pest control: a good example of this is the displacement (increasing rarity) of several native species of ladybird beetle in North America, following the introduction of the Old World species Coccinella septempunctata (7-spotted ladybird beetle) (Louda et al., 2003). In some cases, an introduced control agent has itself become a pest as a result of changing its diet to a useful plant either in preference to the weed or following the demise of the weed for whose control it was imported. There have also been reports that microbial insecticides can infect or cause allergic reactions in humans.

Biological control has not always been successful, though estimates of the degree of success vary. The analysis by DeBach and Rosen (1991) indicated a (partial plus complete) success rate, up to 1988, of about 40% for 416 insect pest species, including 75 species

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.

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