PATTERNS OF DIVERSIFICATION IN PHYTOPHAGOUS INSECTS

Several authors have begun to quantify these rates and their variation. Cook et al.
(2002) used a maximum likelihood approach to show that a genus of cynipid gall wasps
shifts among host plant organs more often than among sections of their host genus, oaks.
Farrell and Sequeira (2004) used similar methods in demonstrating, conversely, that in
chrysomeloid beetles, shift among major host clades outpaces shift among host tissues.
Other reports reinforce this latter trend at the host species level (Condon and Steck 1997,
Favret and Voegtlin 2004). However, studies of gallers are mostly consistent in finding
rapid shift among host tissues (e.g.,Yang and Mitter 1994, Plantard et al. 1997, Nyman et
al. 2000, Dorchin et al. 2004, Joy and Crespi 2007); shifts in gall location, shape and
timing, often on the same host species, may be important facilitators of galler speciation.
Host growth form (i.e., trees vs. herbs) often shows very strong phylogenetic
conservatism relative to host clade (Ronquist and Liljeblad 2001, Bucheli et al. 2002,
Lopez-Vaamonde et al. 2003), but not always (Janz and Nylin 1998, Schick et al. 2003).
Timing of oviposition or development with respect to host phenology is another
dimension of host use which may frequently contribute to speciation, either on the same
host or on a novel host (e.g., Wood 1993, Pratt 1994, Whitcomb et al. 1994, Harry et al.
1998, Filchak et. al. 2000, Weiblen and Bush 2002, Sachet et al. 2006).
A special form of conserved host use, occurring in some groups of aphids and gall
wasps (Cynipidae), is obligate alternation between different host taxa in successive
generations. Host alternation may have originated multiple times in aphids (Moran 1988,
Moran 1992, von Dohlen and Moran 2000, von Dohlen et al. 2006), though this inference
rests mostly on differences in the mode of host alternation and other life history features,
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