DIFFERENTIAL COLONIZATION OF RESISTANT AND SUSCEPTIBLE HOST PLANTS - PEMPHIGUS AND POPULUS

Examines the ability of colonizers to select appropriate hosts when colonization occurs along before feeding, and when traits available as cues may be least associated with host quality; here, precision of host selection may be limited by a lack of appropriate cues at the time of colonization. In the life cycle of the aphid Pemphigus betae, autumn migrants select among host trees (Populus angustifolia and natural hybrids with P. fremontii) far in advance of the spring feeding stages, while trees are in a very different physiological condition. The authors censused successful and aborted galls on 34 trees in a Utah canyon during 7 consecutive years, and estimated attractivity of these trees by censusing autumn migrants during 3 yr. Both survivorship and attractivity varied among trees, and differences among trees persisted across years. Tree-specific colonization rates were positively related to gall establishment. The actual colonization pattern is thus more adaptive than a random colonization process, but the ability to select better hosts is far from perfect. Degree of leaf retention in autumn was positively correlated with both colonization and subsequent progeny survival. The tendency to colonize trees retaining leaves longer in autumn may contribute to P. betae's limited ability to preferentially colonize better hosts. -from Authors