Diversity and Host Plant-Use in North AmericanPhytomyzaHolly Leafminers (Diptera: Agromyzidae): Colonization, Divergence, and Specificity in a Host-Associated Radiation

Abstract

Insects that feed on plants are widely used for studies of host-plant-associated speciation due to their diversity and tractability. The value of these studies necessarily depends upon an accurate understanding of the diet of the focal insects. In North America, the 12 Phytomyza Fallén (Diptera: Agromyzidae) leafmining fly species feeding on hollies (Ilex spp. (Aquifoliaceae: Ilex)) initially appeared to be primarily a host-plant-associated radiation of largely monophagous species. However, our increased collecting efforts found that a majority of the morphospecies are oligophagous, feeding on multiple Ilex species. Patterns of host-associations suggest that colonization of new hosts followed by host-associated speciation may be an important feature of diversification. Analyses of mitochondrial COI data in three oligophagous species found evidence of host-associated genetic structure consistent with processes of host-associated divergence. However, in one of these species, evidence of geographic divergence as well as host-associated divergence was detected, illustrating complexity in factors relating to speciation and host-use evolution in this radiation of leafmining flies.

Manual of North American Agromyzidae (Diptera, Schizophora), with revision of the fauna of the “Delmarva” states

“…While some agromyzids may truly be restricted to a single plant host, it is likely that most can be generally characterised as oligophagous, being limited to multiple hosts in related families or genera. The apparent monophagy of many species will eventually prove to be an artifact of incomplete observations, with a growing body of data revealing that additional rearing records will almost certainly lead to novel host records for many species (Scheffer et al 2021;Eiseman et al 2018Eiseman et al -2021. The extent to which this is true, however, can only be accurately characterised after more targeted taxonomic and rearing studies, and should prove to be a rich field of study.…”

“…Sclerite of hypophallus 1/2-length of mesophallus, apex broadly rounded, base narrow and upcurved (i.e., comma-shaped); Hosts. Aquifoliaceae -Ilex decidua, I. montana, I. verticillata (Scheffer et al 2021 Chaetotaxy: Sometimes very small additional ori present in front of anterior ori, which is 1/2 length of posterior ori. Five scattered rows of acrostichal setulae.…”

“…Hosts. Aquifoliaceae -Ilex glabra, I. coriacea; possibly I. cassine (Scheffer et al 2021 Station, 30.iii.2013, C.S. Eiseman, ex Ilex glabra, em.…”

“…Phytomyza opacae Kulp, 1968: 21. Spencer andSteyskal 1986b: 215;Scheffer 2011: 1198;Scheffer and Lonsdale 2018: 88;Scheffer et al 2021.…”

“…Phytomyza verticillatae Kulp, 1968: 25. Spencer andStegmaier 1973: 123;Spencer and Steyskal 1986b: 214;Griffiths and Piercey-Normore 1995: 23;Scheffer and Wiegmann 2000: 249;Scheffer 2011: 1201;Scheffer et al 2021: 62.…”