Agromyzidae

Phylogenetic Relationships Agromyzids have recently been the subject of two phylogenetic studies investigating relationships among genera within the family (Dempewolf 2001, 2005; Scheffer et al. 2007). Both studies found some support for the two subfamilies, the Agromyzinae and the Phytomyzinae (phylogeny from Scheffer et al. 2007). Neither study included all 29 recognized genera, and in many cases, only one or a few exemplar species within a particular genus were included (Appendix A from Scheffer et al. 2007). However, these studies provide a basic framework for the Agromyzidae that can be further refined as additional phylogenetic studies are completed.

Host-Use Evolution Although many plant families are attacked by agromyzids, the predominant pattern within the Agromyzidae is one of extreme host-specificity of individual species. In combination with the observation that many related agromyzid species feed on related plant species, it is tempting to ask whether host-use patterns within the Agromyzidae have been largely shaped by cospeciation with host plants. Spencer (1990) broadly addressed this question in his consummate treatise on agromyzids, Host Specialization in the World Agromyzidae (Diptera). Although he did not use an explicitly phylogenetic approach, Spencer concluded that there is too much evidence of host switches between distantly related plant groups for overall diversification within the Agromyzidae to have ocurred by a coevolutionary-cospeciation scenerio. However, he did not rule out cospeciation as an explanation for some closely related species-group radiations onto related plants. Although there is now molecular as well as morphological evidence for the monophyly of some of these host-assocaited radiations, to date no studies have presented a detailed phylogeny for both an agromyzid species group and its host plants.

Evolution of Larval Feeding Mode All agromyzid larvae feed within living plant tissue, but the location within the plant can vary and is generally specific to each agromyzid species. Agromyzids typically feed within leaves, stems, flowers, fruits, petioles, cambium, and roots. Most agromyzids with known host affiliations are leafminers, but this is probably due at least in part to the fact that leafminers tend to be more conspicuous than the more concealed feeders in other types of plant tissue. From the information that is available, the larval feeding mode(s) of a number of the agromyzid genera is fairly predictable (however, this is a complicated statement as some generic definitions are based on larval biology, and the monophyly of these genera has yet to be rigorously tested). For some time, it has been suggested that the relatively large concealed feeders inside cambium and/or stems represented the "ancestral" agromyzid feeding mode and that these have repeatedly given rise to the smaller leafmining species. Recent phylogenetic studies offer no support for this hypothesis and instead suggest that early agromyzids were probably leafminers (Dempewolf 2001, 2005; Scheffer et al. 2007).