Host-specificity constrains evolutionary host change in the psyllid Prosopidopsylla flava

1. At the higher taxonomic levels Psylloidea have largely co-evolved with t heir host plants, and the colonisations of new plant lineages have been rel atively few. The mechanisms that have constrained the evolution of host rel ationships throughout the history of this superfamily are not understood. T he host relationships of Prosopidopsylla flava were studied in order to ide ntify possible genetic or ecological constraints to macroevolutionary chang e in host range, using methodology developed for the host specificity testi ng of potential biological control agents. 2. The five Prosopis taxa (Leguminosae) tested appeared to be indistinguish able as hosts. Adult feeding required for survival, and for the initiation and continuation of egg production, was specific to Prosopis species. Ovipo sition occurred on 57 of the 58 non-Prosopis plant species tested within th e Leguminosae and Rosaceae, and was highest on plant species that belonged to the same subfamily. Eggs were inserted into plant tissue by their pedunc le but hatched independently of host species. Complete development was rest ricted to Prosopis, although some early nymphal development was observed on species within the same subfamily as Prosopis (Mimosoideae). 3. Multiple phylogenetic constraints restrict host selection and utilisatio n by P. flava to Prosopis species, implying a long association between inse ct and host. Specificity of adult feeding was of special significance, bein g required for survival, oogenesis, and probably indirectly determining the oviposition host. This supports the hypothesis that genetically set limits in particular aspects of life history are responsible for the inability of some psyllids to readily colonise new plant lineages, rather than stabilis ing selection.