Host Relationships, Life Cycles, and Systematics of Aphids of the Genus Uroleucon.

As in many herbivorous insects, degree of host specificity varies widely in the genus Uroleucon (Homoptera: Aphididae), which feeds on plants of the family Compositae. Host records and preference experiments reveal that the generalist U. gravicorne tends to specialize at any one time on a subset of potential hosts. Perennial Solidago species are used most in spring and fall and annual Erigeron in mid-summer, a pattern convergent with that of aphids which move obligately between woody plants and herbs. Reproductive performance, as reflected in size, developmental time, and fecundity, is relatively high on Solidago in spring and on Erigeron in summer, in keeping with host usage. However, return to Solidago in fall may function more to provide good oviposition sites than to provide superior fall nutrition. When compared on their common host during spring, the specialist U. nigrotibium attains a larger size, develops slightly faster, and has slightly greater fecundity than the generalist U. gravicorne. Except for size, this advantage disappears in summer and fall. Censuses of field colonies and behavioral experiments show that the specialist displays distinctive features, including few alatae, frequent walking between plants, and a readiness to drop from hosts to avoid natural enemies. Due to interdependence of host breadth, dispersal mode, and predator escape tactics, metabolic efficiency cannot be regarded as the sole variable affecting degree of specificity. Furthermore, nigrotibium actually develops faster, becomes larger, and is more fecund on a non-host during spring, so that its specificity cannot be explained by metabolic specialization alone. The 33 species of Uroleucon collected in Michigan comprise 3/4 of the eastern North American fauna and include three new species, U. cadens, U. gigantiphagum, and U. olivei. A key and host plant information are presented. Offspring sex is under maternal control in aphids; thus, their sex ratios are of special interest. Some eriosomatines have female biased broods, apparently due to a history of local mate competition. Biases, due to various life cycle patterns, are predicted for other aphid groups.PhDEntomologyUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/159240/1/8304552.pd