Taxonomic diversity and interactions of insect-associated ascomycetes MEREDITH BLACKWELL and KEVIN JONES Department of Plant Biology, Louisiana State University, Baton Rouge, LA 70803, USA Received 25 July 1996; accepted 18 August 1996 Many ascomycetes are associated with insects to form symbioses. The fungi are necrotrophic and biotrophic parasites, endosymbionts, insect-dispersed forms, and other obligate associates that provide nourishment for insects. Diversity among these fungi can be categorized in several dierent ways: taxonomic diversity, variety of interaction types occurring within a fungal lineage, and number of fungal species. Previously our inability to produce well supported phylogenetic hypotheses has obscured these views of diversity. Over the past 5 years our knowledge of insect-associated fungi has been improved by the use of DNA sequence analysis. Such studies have revealed that ascomycetes in almost all major clades are associated intimately with insects. Of particular interest has been the sorting out of relationships of taxa with convergent morphologies, unique characters, and lost characters, including those associated with sexual reproduction. Within some fungal groups the types of interactions with insects are diverse, and eventually phylogenetic analysis will help to trace the evolutionary development of symbioses. Molecular studies also contribute to our understanding of the number of species which may vary according to species concepts used in their study. Keywords: ascomycetes; insects; mites; symbiosis; interactions; rDNA. Introduction Insects and fungi are closely associated in most environments, and many types of inter- action that have arisen repeatedly have been observed among diverse taxa of these groups of organisms. The interactions may be categorized roughly as necrotrophic and biotrophic parasitism, dispersal and fertilization associations, gardening symbioses, and endosymbioses (Batra, 1979; Bultman and White, 1988; Pirozynski and Hawksworth, 1988; Samson et al., 1988; Wilding et al., 1989; Carroll and Wicklow, 1992). The inter- actions sometimes are extremely complex and may involve other organisms in addition to fungi and insects (Blackwell et al., 1986; Price, 1991). Our knowledge of the diversity (the number of taxonomic groups of insect fungi, the variety of interactions occurring within each fungal lineage and their histories, and number of fungal species) has been improved by the use of phylogenetic analysis of molecular characters. Methods and materials The techniques used for DNA extraction, polymerase chain reaction, sequencing, and data analysis have been published elsewhere (Spatafora and Blackwell, 1993, 1994a, b; Cassar and Blackwell, 1996; Jones and Blackwell, 1996), and some information is given in the figure legends. DNA sequences used in the analyses and their sources are shown in Table 1. Although some new data are discussed, they will be published in detail elsewhere. 0960-3115 Ó 1997 Chapman & Hall Biodiversity and Conservation 6, 689–699 (1997)