9527950 DeSalle The range of host plants used by groups of insects can be broad or very narrow, including host plant specificity or restriction to a single host. Since most insects, which constitute the vast majority of all animal species, use plants during some part of their life cycles for food or as a place to reproduce, it is important to understand the causes for insects to be host specialists or generalists. Patterns of host use may be important in explaining the diversification of insect groups. Particular aspects of host plants may either limit or increase the number of hosts an insect species can use. Over long time intervals, this may give rise to related groups of insect species that share host affinities. The research project supported by this award will use patterns of DNA sequence data similarities to study the degree of genetic relatedness among a group of over 40 species in the Drosophila mulleri species complex (Insecta: Diptera: Drosophilidae). The pattern of species relationships determined will be compared to the host use of these species in nature. Two clusters of species in this complex, each with three species, will be studied in greater detail for evidence of population level variation in DNA sequence data. The fruit flies in this study group breed on cacti and their larvae feed on cactus host plants. There has been an apparent host shift with some species feeding on the cactus genus Opuntia, whose members are easily recognized by paddle shaped parts, to other cacti whose growth form is columnar or barrel shaped. Knowledge of relationships among the Drosophila species will allow determination of the number of times that this shift between cactus types has occurred. %%% This award will provide information on the biodiversity and host plant associations in a group of specialized cactus feeding flies. This research represents an important model system for understanding host shifts and the origin of insect pests that may be of value in developing non-chemica l means of controlling pests. ***
