464
the AT content of non-parasitoid sawflies of Symphyta, including Orussidae
(Dowton and Austin 1995a). This extreme codon bias likely occurred during the
Early Jurassic, attributable to a founder event reflective of the parasitoid lifestyle
(Dowton and Austin 1995b). Because of this causal link between sequence divergence of mitochondrial DNA and parasitoid life habits (Dowton and Austin 1995a),
larval sawflies of Symphyta, the basal-most group, would have gone through a predaceous life habit prior to parasitoidism (Morris 1998). Such a life habit could have
been present in enclosed feeders such as gallers (Tenthredinidae) or wood borers
(Siricidae), in which a feeding strategy included consumption of arthropod cohabitants, including cannibalism, as a trophic prelude to the parasitoid life habit.
Facilitating this nutritional transition to the parasitoid condition would be modification of the rigid, cutting ovipositor of a sawfly into a much longer, flexible, piercing
or drilling ovipositor of basal Apocrita (Fig. 11.1f), allowing access to larvae
through a few centimeters of hard substrates such as wood (Gauld and Bolton 1988).
Hymenoptera transformed their sawfly ovipositor into a singular structure that
allowed boring and drilling into considerable depths of plant tissue for inserting
eggs on or in target larvae. In the process of ovipositor piercing and drilling into
plants, chemicals were injected to soften wood, sclerenchyma and other indurated
tissues that allowed attack of larval insects within enclosed plant tissues (Gauld and
Bolton 1988; Morris 1998). This structural transformation of the ovipositor is considerably different that the condition in Diptera, the other major clade of parasitoid
insects, and accounts for the exceptional reach of hymenopteran parasitoids in targeting host larvae.
Orussoidea are a superfamily of sawflies that either have a sister-clade relationship or are paraphyletic to Apocrita. They are ectoparasitoids of wood wasps such
as Siricidae or wood-boring beetles such as Buprestidae in dead wood (Gauld and
Bolton 1988; Vilhelmsen and Turrisi 2011). A series of basal Apocrita superfamilies
of Stephanoidea, “Ephialtitoidea” (Fig. 11.1f), Megalyroidea and Evanioidea are
almost all ectoparasitoids of wood-boring larvae that have an overall geochronologic distribution ranging from Early Cretaceous to Recent (Whitfield 2003;
Moghaddam and Turrisi 2018; Li et al. 2018a). Within these superfamilies, several
extinct, family-level lineages range from late Early Jurassic to mid Cretaceous and
are presumed to have similar biologies based on their phylogenetic position within
modern lineages of known biologies. One exception to the exclusive ectoparasitoid
habits of Stephanoidea, Megalyroidea, Evanioidea and probably “Ephialtitoidea” is
the superfamily Trigonalyroidea in which Trigonalidae is an endoparasitoid on
external-foliage-feeding, folivorous larvae (Weinstein and Austin 1991; Engel 2016).
The Proctotrupomorpha, the most diverse, monophyletic clade (sensu Castro and
Dowton 2006) of parasitoid insects, consists of the apocritan superfamilies
Proctotrupoidea, Cynipoidea, Platygastroidea, Chalcidoidea, Mymarommatoidea
and Serphitoidea (Table 11.1). In many analyses, Proctotrupomorpha also includes
the Ceraphronoidea and Ichneumonoidea (Castro and Dowton 2006); by contrast, in
other studies these superfamilies are excluded (Dowton et al. 1997; Sharanowski
et al. 2010). (The more encompassing view is taken here.) The next three superfamilies are endoparasitoids, the first two of which, Proctotrupoidea and Cynipoidea,
C. C. Labandeira and L. Li
the AT content of non-parasitoid sawflies of Symphyta, including Orussidae
(Dowton and Austin 1995a). This extreme codon bias likely occurred during the
Early Jurassic, attributable to a founder event reflective of the parasitoid lifestyle
(Dowton and Austin 1995b). Because of this causal link between sequence divergence of mitochondrial DNA and parasitoid life habits (Dowton and Austin 1995a),
larval sawflies of Symphyta, the basal-most group, would have gone through a predaceous life habit prior to parasitoidism (Morris 1998). Such a life habit could have
been present in enclosed feeders such as gallers (Tenthredinidae) or wood borers
(Siricidae), in which a feeding strategy included consumption of arthropod cohabitants, including cannibalism, as a trophic prelude to the parasitoid life habit.
Facilitating this nutritional transition to the parasitoid condition would be modification of the rigid, cutting ovipositor of a sawfly into a much longer, flexible, piercing
or drilling ovipositor of basal Apocrita (Fig. 11.1f), allowing access to larvae
through a few centimeters of hard substrates such as wood (Gauld and Bolton 1988).
Hymenoptera transformed their sawfly ovipositor into a singular structure that
allowed boring and drilling into considerable depths of plant tissue for inserting
eggs on or in target larvae. In the process of ovipositor piercing and drilling into
plants, chemicals were injected to soften wood, sclerenchyma and other indurated
tissues that allowed attack of larval insects within enclosed plant tissues (Gauld and
Bolton 1988; Morris 1998). This structural transformation of the ovipositor is considerably different that the condition in Diptera, the other major clade of parasitoid
insects, and accounts for the exceptional reach of hymenopteran parasitoids in targeting host larvae.
Orussoidea are a superfamily of sawflies that either have a sister-clade relationship or are paraphyletic to Apocrita. They are ectoparasitoids of wood wasps such
as Siricidae or wood-boring beetles such as Buprestidae in dead wood (Gauld and
Bolton 1988; Vilhelmsen and Turrisi 2011). A series of basal Apocrita superfamilies
of Stephanoidea, “Ephialtitoidea” (Fig. 11.1f), Megalyroidea and Evanioidea are
almost all ectoparasitoids of wood-boring larvae that have an overall geochronologic distribution ranging from Early Cretaceous to Recent (Whitfield 2003;
Moghaddam and Turrisi 2018; Li et al. 2018a). Within these superfamilies, several
extinct, family-level lineages range from late Early Jurassic to mid Cretaceous and
are presumed to have similar biologies based on their phylogenetic position within
modern lineages of known biologies. One exception to the exclusive ectoparasitoid
habits of Stephanoidea, Megalyroidea, Evanioidea and probably “Ephialtitoidea” is
the superfamily Trigonalyroidea in which Trigonalidae is an endoparasitoid on
external-foliage-feeding, folivorous larvae (Weinstein and Austin 1991; Engel 2016).
The Proctotrupomorpha, the most diverse, monophyletic clade (sensu Castro and
Dowton 2006) of parasitoid insects, consists of the apocritan superfamilies
Proctotrupoidea, Cynipoidea, Platygastroidea, Chalcidoidea, Mymarommatoidea
and Serphitoidea (Table 11.1). In many analyses, Proctotrupomorpha also includes
the Ceraphronoidea and Ichneumonoidea (Castro and Dowton 2006); by contrast, in
other studies these superfamilies are excluded (Dowton et al. 1997; Sharanowski
et al. 2010). (The more encompassing view is taken here.) The next three superfamilies are endoparasitoids, the first two of which, Proctotrupoidea and Cynipoidea,
C. C. Labandeira and L. Li