PATTERNS OF DIVERSIFICATION IN PHYTOPHAGOUS INSECTS

Ancient host associations in other phytophagous lineages that date to the early
Mesozoic and before, less well characterized, await clarification by modern studies.
Recent progress on phylogeny of sawflies (basal hymenopterans; e.g., Schulmeister
2003), modern families of which date to the early Jurassic or even Triassic, should permit
elucidation of the degree to which the multiple conifer (& fern) feeding lineages, totaling
several hundred species, represent ancestral habits. We can hope for similar
enlightenment about the Aphidomorpha (aphids and relatives), probably Triassic in age,
in which the phylogenetic positions of the few extant gymnosperm-associated lineages
are still obscure (Heie 1996, Normark 2000, von Dohlen and Moran 2000, Ortiz-Rivas et
al. 2004). Moreover, documentation of such deep-level relictual host associations may
prompt re-examination of some younger groups for which synchronous diversification
with hosts seems at first glance implausible. Thus, analysis of the 1000+ species of
cynipid gall wasps detected no significant overall phylogeny match with their host plant
families, mostly woody rosids and herbaceous asterids (Ronquist and Liljeblad 2001).
However, recently-discovered taxa have raised the possibility that the ancestral gall
wasps, like one basal extant lineage, fed on Papaveraceae, a member of the most basal
eudicot lineage, Ranunculales (but see Nylander 2004, Nylander et al. 2004). Fossils date
the gall wasps to at least the late Cretaceous, thus it is possible that this habit has been
retained since before the rise to prominence of the host groups commonly used today
(Ronquist and Liljeblad 2001). A similar history is possible for some genera of
leafmining agromyzid flies (Spencer 1990).
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