Biological control of livestock pests: Entomopathogens

Interest in biological methods for livestock and poultry pest management is largely motivated by the development of resistance to most of the available synthetic pesticides by the major pests. There also has been a marked increase in organic systems, and those that promote animal welfare by reducing animal densities and allowing greater freedom of movement. Such systems, especially organic operations, are in need of new tools and strategies to manage pest problems. This chapter reviews the status of entomopathogenic fungi, viruses, and nematodes for management of pests of livestock and poultry production. The pests covered here are limited to the research that has been conducted to date, but include biting and nuisance flies, ticks, poultry ectoparasites, and litter beetles. Many of the same pests affect horses as well, although little work has been done in this area. The fungal pathogens Beauveria bassiana and Metarhizium anisopliae s.l. have received the most attention and have been evaluated against most of the major livestock and poultry pests. These pathogens have the greatest potential for practical use, but more work is needed to identify efficacious isolates and develop formulations for both on- and off-host use. The slow kill rate of these pathogens has been considered a liability in the past, but a growing body of work has demonstrated important sublethal effects of infection that includes reduced feeding, movement, and pathogen transmission. Two pathogens of house fly, the fungus Entomophthora muscae and salivary gland hypertrophy virus, are effective under some conditions but have biological characteristics that have limited their development as practical management tools. Entomopathogenic nematodes (Steinernema and Heterorhabditis spp.) also have potential but are limited by environmental constraints, especially temperature and substrate moisture. Discovery of, or selection for, strains with wider environmental tolerance could broaden the range of situations where they can be used effectively.