Insects And Humans

those required for development of natural epizootics, timely irrigation so as to provide the 761

humidity necessary to precipitate a fungal epizootic, and minimum tillage cultivation to avoid the destruction of pathogens in the upper soil layer.

Microbial products constituted about 2% of the world pesticide market by the mid-1980s. This share was expected to increase considerably as the technological problems referred to earlier were overcome and dissatisfaction with chemical insecticides continued to increase (Roberts, in Pimentel, 1991, Vol. 2). However, this has not been the case, perhaps in large part due to the development of cheaper and safer chemical insecticides, especially synthetic pyrethroids.

The potential ofbacteriaasmicrobial control agents remains largely untapped,with only five species (Bacilluspopilliae, B. lentimorbus, B. thuringiensis, B. sphaericus, and Serratia entomophila) available commercially. Commercialization of the two milky disease-causing species (B. popilliae and B. lentimorbus) is of interest because they are obligate pathogens, which has necessitated their production in living hosts either collected from the field or grown in laboratory culture and harvesting the spores from the cadavers. B. sphaericus is registered for mosquito control and is especially effective against species of Culex. S. entomophila is available in New Zealand for control of the grass grub Costelytra zealandica.

B. thuringiensis (Bt) is by far the most successful microbial control agent, with several million kilograms being produced annually. Commercial formulations of a number of its subspecies (notably kurstaki, israelensis, and tenebrionis) are available for more than 100 species, mostly lepidopterous and coleopterous pests of forest and agricultural (including stored products) pests, and for mosquitoes and black flies (Table 24.7). The great advantage of Bt is that it can be cultured outside its hosts by liquid fermentation using cheap sources of protein such as soy meal. As noted earlier, however, Bt is short-lived, and several applications may be necessary each season. Furthermore, several examples of pests developing some degree of resistance to Bt are now known (Beegle and Yamamoto, 1992; Tabashnik, 1994; Koul and Dhaliwal, 2002). Currently, considerable effort is being devoted to genetically engineering Bt so as to improve its persistence, specificity, and toxicity. Among the possibilities being explored are adding more or improving the toxin genes, engineering the toxin gene into other organisms, including other bacteria that are more resistant to weathering and host plants whose foliage will thus produce the toxin (Sheck, in Pimentel, 1991, Vol. 2; Khetan, 2001). For additional information on Bt, see also Margalit and Dean (1985), Luthy (1986), van Frankenhuyzen (1990), Milner (1994), and Metz (2003).

Though Table 24.8 would suggest that viruses (especially nucleopolyhedroviruses) are important microbial control agents, their commercialization and use by producers has been slow, primarily for three reasons; they are too expensive to produce, too slow to act, and too host-specific (Payne, 1986; Roberts etal. inPimentel, 1991, Vol. 2; Hunter-Fujita etal., 1998; Federici, in Bellows and Fisher, 1999; Moscardi, 1999; Khetan, 2001; Koul and Dhaliwal, 2002). A notable exception is the nucleopolyhedrovirus (AgNPV) that infects the velvetbean caterpillar (Anticarsia gemmatalis). AgNPV is applied annually to more than 1 million hectares in Brazil (and to smaller areas in some other South American countries) for control of this pest in soybean (Moscardi, 1999). Economically, viruses generally have not yet been able to compete with chemical insecticides, primarily because of their host specificity and their obligate parasitism. Because they must be ingested to be effective, it takes several days before their lethal effect is manifest, during which the pest may do considerably more damage. Other disadvantages include their sensitivity to sunlight (though in soil or litter they can survive from season to season) and, apparently, the existence of significant resistance by pests to them. Advantages of viruses include their specificity (especially in integrated pest management), environmental safety, compatibility with other

TABLE 24.7. Some Insect Pests of Agriculture and Forestry with Potential for Management by Formulations of Bacillus thuringiensis S-Endotoxina

Cruciferous crops

Cotton and tobacco

Corn

Potatoes

Soybean, canola, forage crops

Tobacco Tree fruits

Stored grains Forests and ornamentals

Pieris rapae (imported cabbageworm), Plutella xylostella (diamondback moth), Trichoplusia ni (cabbage looper)

Heliothis virescens (tobacco budworm)

Ostrinia nubilalis (European corn borer)

Leptinotarsa decemlineata (Colorado potato beetle)

Anticarsia gemmatalis (velvetbean caterpillar), Mamestra configurata (bertha armyworm), Spodoptera exigua (beet armyworm), S. frugiperda (fall armyworm)

Manduca quinquemaculata (tomato hornworm), M. sexta (tobacco hornworm)

Archips argyrospilus (fruit-tree leafroller), Argyrotaenia volutinana (red-banded leafroller), Operophtera brumata (winter moth), Spilonota ocellana (eye-spotted bud moth)

Cadra cautella (almond moth), Plodia interpunctella (Indian meal moth)

Choristoneura fumiferana (spruce budworm), C.occidentalis (western spruce budworm), Dioryctria amatella (southern pine coneworm), Lambdina fiscellaria fiscellaria (hemlock looper), Lymantria dispar (gypsy moth), Malacosoma americanum (eastern tent caterpillar), M. disstria (forest tent caterpillar), Pryganidia californica (California oakworm), Pyrrhalta luteola (elm leaf beetle)

biological control agents, and relative simplicity of their genome. The latter has facilitated genetic engineering to improve their usefulness: in particular, recombinant DNA technology has been used to incorporate toxins, resulting in a 20% to 40% reduction in killing time (Bonning and Hammock, 1996; Federici, in Bellows and Fisher, 1999; Bonning etal., 2003).

As was noted in Chapter 23, Section 5.2.4, it was a fungus (Metarhizium anisopliae) that was the control agent in the first attempt at microbial control. Generally speaking, however, the potential of fungi as pest control agents has not been widely exploited, perhaps for three main reasons: inconsistency of test results (probably because of a lack of understanding of the factors that regulate spore germination and infectivity), a perceived impracticability of using fungi because, under natural conditions, their epizootics are heavily dependent on weather conditions, and early concern about their safety because some fungi that are insect pathogens are also known to affect vertebrates (Roberts, in Bulla, 1973). Other disadvantages include inactivation by sunlight and the potential for incompatibility with other components of pest control, notably fungicides for plant diseases and some

TABLE 24.8. Viruses Used Successfully for Insect Pest Management

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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