Insects And Humans

expected by users and the former providing long-term protection. Some studies have shown 765

that pests are more susceptible to insecticides (thus, less need be applied) when treated simultaneously with a protozoan pathogen (Henry, 1981; Wilson, 1982; Roberts et al., in Pimentel, 1991, Vol. 2).

As noted in Chapter 23 (Section 5.2.6), the numerous species of nematodes that attack insects fall into two major categories: parasites and pathogens. Generally, there has been little interest in determining the potential of parasitic species as biological control agents, although more than 30 years ago the importance of the facultatively parasitic Deladenus siricidicola (Neotylenchidae) as a control agent for the wood wasp Sirex noctilio was recognized (Bedding, 1984, 1993). This European wasp, introduced into New Zealand in the early 1900s, Australia in the 1950s, and South America in the 1980s, is a major pest of pines, especially Monterey pine (Pinus radiata), a major timber species. The free-living stage of D. siricidicola can be mass-produced on fungi grown in vitro. It is then injected into holes bored in infected pines, where it is able to locate and infect wood wasp larvae. With this method, parasitism rates up to 90% were obtained, reducing the number of trees killed to zero over a 4-year period in Tasmania.

Over the past 25 years, there has been an exponential increase in interest in the commercialization of pathogenic nematodes against insect pests, specifically the Steinernematidae and Heterorhabditidae which possess a number of attributes relevant to pest control, including a very wide host range, high virulence, ease of large-scale production in artificial media, durability of the infective stage, and safety (hence, the United States Environmental Protection Agency has exempted them from government registration requirements). As well, the infective larval stage is mobile and can actively seek out its insect host. Disadvantages are those typical of microbial agents, especially sensitivity to sunlight, desiccation, and high temperature, as well as poor storage qualities. Thus, nematode products find their greatest use in situations where the pathogens are protected from environmental extremes, for example, against soil pests and pests living in cryptic habitats. Commercial formulations of at least eight species of pathogenic nematodes are available worldwide, though Mrácek (in Upadhyay, 2003) lists more than a dozen species that have been used in small and large-scale biological control programs. From an economic perspective, nematodes rank second to bacteria in importance as microbial pesticides. Among the pests for which they are used are termites, cutworms, flea larvae, mole crickets, white grubs, various soil-dwelling fly larvae, and root weevils, as well as slugs and plant nematodes (Poinar, 1986; Gaugler and Kaya, 1990; Roberts et al., in Pimentel, 1991, Vol. 2; Bedding et al., 1993; Flexner and Belnavis, in Rechcigl and Rechcigl, 2001; Mrácek, in Upadhyay, 2003). Experimentally it has been demonstrated that many insect species which do not normally encounter pathogenic nematodes are nevertheless susceptible to them. Thus, technological developments such as the addition of antidesiccants to the formulation, genetic selection of more desiccation-resistant strains, and genetic engineering should improve the pest spectrum against which nematodes can be used (Liu et al., 2000; Brey and Hashmi, in Upadhyay, 2003).

In conclusion, it is evident that pathogenic microorganisms will play an increasing role in insect pest management strategies in the foreseeable future. Both technological developments, aimed at improving the production and delivery of these bioinsecticides, and genetic manipulations to increase their viability, virulence, specificity, and other useful features will be vital to their success (Harrison and Bonning, in Rechcigl and Rechcigl, 2000). The majority of bioinsecticides will be used in a manner analogous to the chemicals that they will (partially) replace, and caution must be used, for example, to prevent the development of resistance. Scattered examples of resistance to representatives of all of the

766 major groups of pathogenic microorganisms can be cited; indeed, this would be expected in view of the long coevolutionary relationship between the pest and its pathogen. However,

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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