bassiana (Balsamo) Vuillemin, Metarhizium anisopliae (Metschnikoff) Sorokin, Verticillium lecanii (Zimmerman) Viegas, and Paecilomyces spp., all of which have worldwide distributions; these are the most commonly used insect pathogens developed for commercial pest-management products (McCoy 1990).

B. bassiana has been identified in many insect species in temperate and tropical regions and is used for pest control on a moderate scale in eastern Europe and China. Mycogen produced a B. bassiana-based bioinsecticide, which has been shown to be highly pathogenic in coleopterans. The fungus also is amenable to mass production of conidia by semi-solid fermentation. The product has been field-tested against citrus root weevil. Another B. bassiana strain, researched at the USDA ARS shows good control of rasping or sucking insects, such as thrips, whiteflies, and aphids.

M. anisopliae has been most extensively used in Brazil for control of spittlebugs on sugar cane. Using Metarhizium as the control agent, EcoScience Laboratories, Inc. has developed infection chambers in which insects (cockroaches and flies) brush against spores of the pathogen, which later germinate and infect the insect. However, this product has not been successfully commercialized.

V. lecanii is a pathogen that has demonstrated good control of greenhouse pests, such as Myzus persicae (Sulcer) aphids, on chrysanthemums. A distinct isolate of V. lecanii was obtained from whitefly and provided excellent control of greenhouse whitefly, Trialeurodes vaporariorum (Westwood), and of Thrips tabaci Lindeman on cucumber. V. lecanii was produced commercially as Vertalec for aphid control and Mycotal for control of whitefly from 1982 to 1986, and there is a resurgence of commercial interest in its use for control of aphids, whiteflies, and thrips because these greenhouse pests have developed resistance to chemical pesticides typically used for their control.

The fungal pathogen Entomophaga maimaiga has been recognized and used by USFS, states' departments of natural resources, and university personnel as a control for gypsy moth (Elkinton et al. 1991). Since its reappearance in the early 1990s, this pathogen largely has become self-perpetuating. It should be noted that public research agencies have played an important role in the development of gypsy moth pest-management strategies. In fact, the use of Entomophaga maimaiga with Bt and NPVs exemplifies the trend toward biologically based pest management in gypsy moth control in the last 10 years.

The effectiveness of fungi in controlling insect pests depends on the environmental conditions prevailing after application, particularly with respect to relative humidity. There is a need for research to develop moisture-retaining formulations that allow fungal growth at suboptimal rela-

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