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716 such as NPVs and CPVs, are able to survive outside the host for a considerable time under suitable conditions (e.g., in soil, in leaf litter, on tree bark, and in cadavers). Cabbage looper NPV, for example, may persist for 9 years in soil. Viruses are relatively stable within the temperature and humidity range that they normally experience. However, they are sensitive to sunlight, especially its shorter (ultraviolet) wavelengths, and are inactivated by a few hours of continuous exposure. Thus, those that are disseminated on the host's food plant may have limited viability. In commercial preparations viability is increased by additives that screen out ultraviolet radiation. Viruses are also sensitive to pH and need to be maintained in conditions close to neutrality. Again, in commercial preparations such sensitivity may be partially overcome by the inclusion of buffers.

The best-studied (and most-commercialized) viruses are the baculoviruses, which are restricted to invertebrate (mostly insect) hosts and are structurally dissimilar to mammalian or plant viruses (Moscardi, 1999; Battu etal., 2002). Of these, NPVs have been isolated from numerous Lepidoptera and from representatives of other orders, whereas GVs apparently are restricted to Lepidoptera. Though the majority of pest Lepidoptera are susceptible to NPVs and/or GVs under experimental conditions, for relatively few of these have the viruses been used successfully in integrated pest management (see Table 24.8). In rare cases, for example, Gilpinia hercyniae (European spruce sawfly) in Canada, NPVs exert a strong degree of natural control so that populations of this potential pest do not reach epizootic levels.

IVs have been isolated mainly from Diptera, including mosquitoes and black flies. Though highly infective when injected experimentally into the hemocoel, IVs do not appear to have much future as biological control agents in Diptera, at least, because they are rapidly destroyed when ingested. Further, the peritrophic matrix of dipteran larvae does not have gaps like that of larval Lepidoptera (David, 1975).

Almost all of the approximately 150 species of insect from which CPVs have been isolated are Lepidoptera, and a number of these are pests. Relatively little work appears to have been carried out on the potential of CPVs as control agents, perhaps because many of the pests in which they occur are also susceptible to the better-known NPVs and because they are relatively slow-acting.

Studies on entomogenous fungi, including their potential as control agents, tend to be overshadowed by the enormous volume of work being carried out on bacteria and viruses. However, the first attempt at microbial control (by Metschnikoff in 1879 against larvae of the wheat cockchafer, Anisoplia austriaca) used the green-muscardine fungus, Metarhizium anisopliae, and the first large-scale program in the United States, which covered almost the whole of Kansas, began in about 1890 against the chinch bug, Blissus leucopterus, using the fungus Beauveria bassiana (Glare and Milner, 1991).

Unlike bacteria, viruses, and protozoa, fungi normally enter insects via the integument rather than the gut, whose conditions (especially pH) are unsuitable for fungal spore germination. They are the principal pathogens of sucking insects, which cannot ingest pathogens whose route of entry is the gut wall. They are also important disease-causing agents of Coleoptera, which seem especially resistant to viral and bacterial diseases (Hajek and St. Leger, 1994). Apart from suitable temperature and pH (in soil-dwelling fungi), high humidity or even liquid water is essential for spore germination, an observation that accounts for the frequent occurrence of fungal epizootics during periods of rainy or humid weather. After germination, access through the cuticle is probably achieved through the secretion of chitinase and proteinase enzymes by elongating hyphae. Initially, the hyphae that penetrate

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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