Showing papers by "Richard A. Humber published in 1997"

Chapter V-1 – Fungi: Identification

Abstract: Publisher Summary This chapter presents the basic skills and information needed to allow nonmycologists to identify the major genera and the most common species of fungal entomopathogens to the generic. Major species of fungal entomopathogens have basic diagnostic characters making them quickly identifiable. The identification of most entomopathogenic fungi necessarily depends on the observation of microscopic characters. Vegetative states of most fungi have little taxonomic value and are not characterized in the key. It is suggested that if no spores are seen in a collection, specimens should be incubated for a further time in room conditions of temperature, humidity and light. Outside the Entomophthorales, the only other significant associations with arthropods are found in the Trichomycetes, a diverse group of fungi that are mainly endocommensal in the guts of insects or crustaceans. Watermolds produce uni- or biflagellate zoospores that are both dispersive and infective units. Flagellate zoospores may be released from two possible sorts of sporangia, those with either thin or thick walls. It would be unusual to detect hosts infected by these fungi during their vegetative states, as these fungi are usually only detected when sporangia have been formed or are releasing zoospores.

Fungi: Preservation of cultures

Abstract: Publisher Summary This chapter discusses preservation of microbial cultures. Storing fungi, at ambient temperatures rather than in refrigeration, may require fewer resources than any other preservation strategy. Storing culture, slants under a layer of sterile mineral oil, is one of the oldest, simplest and least expensive methods for long-term culture preservation. Cultures kept under mineral oil may remain viable for decades. Pathogenicity of entomopathogenic fungi may be undiminished after several months of storage. Storage of metabolically inactive fungi under sterile distilled water may be least technologically demanding of any preservation techniques. Lyophilization may be one of the most widely used technologically sophisticated approaches to preserve fungal germplasm and is the primary technique used in most general service culture collections. Standard domestic freezers might seem to be an ideal and economical tool for keeping frozen cultures. The use of anhydrous silica gel crystals as a carrier for culture propagules is limited to aerobic bacteria and fungi that grow on solid culture media. The choice of cryoprotectant determines the temperature, the heat of fusion, at which the cryoprotectant freezes with a strongly exothermic reaction. It is observed that the laboratory that relies on nitrogen storage facilities has made a long-term and expensive commitment to maintain cultures perceived as having a very high intrinsic value.

Formation and germination of Entomophaga maimaiga azygospores

Abstract: Azygospores (resting spores) of the gypsy moth fungal pathogen Entomophaga maimaiga are produced in abundance during late spring and early summer in late-instar gypsy moth larvae (Lymantria dispar)...

Entomopathogenic hyphomycetes associated with gypsy moth larvae

Abstract: Gypsy moth, Lymantria dispar, popula- tions were sampled in four eastern North American states during 1991 and 1992 to evaluate levels of hy- phomycete infection in association with releases of the Asian gypsy moth pathogen Entomophaga mai- maiga. Paecilomyces farinosus was the most abundant hyphomycete species, occurring at the majority of sites, although levels of infection averaged only 4.6% (1991) and 12.2% (1992). In the plots sampled, con- current levels of infection by E. maimaiga averaged 22.2 ± 5.5 during 1991 and 71.4 ± 12.7% during 1992 but there was no association between preva- lence of P farinosus and E. maimaiga. Beauveria bas- siana was the only other hyphomycete killing larvae in the field but its occurrence was rare. Verticillium