468
(Kathirithamby 2009; Beutel et al. 2016). Similarly, in Diptera the eggs are scattered in the general vicinity of the host. Upon hatching, a special, mobile, first-instar
larva of the parasitoid, the planidium, searches for the host via various chemical and
physical cues (Askew 1971). Three main nutritional regimes are present to which
Hymenoptera have shifted from parasitoid ancestors. First, predation was acquired
indirectly via larval provisioning of paralyzed hosts by aculeate bees and wasps, or
directly from the parasitoid life habit, such as some ichneumonoid wasps (Eggleton
and Belshaw 1992). Second, Hymenoptera parasitoid to phytophage transitions
occurred in several families that formerly fed on larvae in highly nutritious habitats
such as leaf mines and galls, the Cynipidae being the best example (Fergusson
1990). Third, transitions from egg parasitoidism to egg predation are documented in
Evaniidae (Askew 1971). Parasitoidism is a widespread life habit in Hymenoptera
that is a rich source of secondary predation and phytophagy.
11.6 Modern Food Webs and the Mid-Mesozoic Parasitoid
Revolution (MMPR)
Much of the ensuing discussion references Fig. 11.19, which documents the diversity of major parasitoid clades and groups from the time of their initial appearance
during the late Early Jurassic to their representation in the recent record. The fossil
diversity of seven major clades or groups of parasitoids—non-proctotrupomorph
Hymenoptera, proctotrupomorph Hymenoptera, aculeate Hymenoptera, noneremoneuran Diptera, eremoneuran Diptera, Strepsiptera and Coleoptera—record
first the establishment of the Mid-Mesozoic Parasitoid Revolution (MMPR) and
then the subsequent expansion of parasitoid groups and clades through time. Other
clades with rare parasitoid members—Neuroptera, Trichoptera and Lepidoptera—
each contain one or two families of parasitoid taxa that are not included because of
an insufficient or irrelevant fossil record. The MMPR is a time interval during the
late Early Jurassic to late Early Cretaceous (phases 1 and 2) in which bottom-to-top
regulation of terrestrial food webs dominated by inefficient clades of predators were
replaced by top-to-bottom trophic regulation by considerably more efficient parasitoid clades. After the MMPR, these clades subsequently expanded (phases 3 and 4)
as parasitoids became trophically entrenched in terrestrial food webs to the present
day. The initial pulse of the MMPR consisted of phases 1 and 2 that represented the
earliest occurrences and establishment of most parasitoid lineages in terrestrial habitats from the latest Early Jurassic (Toarcian Stage) to the Early Cretaceous (Albian
Stage). Commencing with the Late Cretaceous is the subsequent evolutionary diversification and ecological expansion of parasitoids represented by phases 3 and 4 that
continues to the present day.
C. C. Labandeira and L. Li
(Kathirithamby 2009; Beutel et al. 2016). Similarly, in Diptera the eggs are scattered in the general vicinity of the host. Upon hatching, a special, mobile, first-instar
larva of the parasitoid, the planidium, searches for the host via various chemical and
physical cues (Askew 1971). Three main nutritional regimes are present to which
Hymenoptera have shifted from parasitoid ancestors. First, predation was acquired
indirectly via larval provisioning of paralyzed hosts by aculeate bees and wasps, or
directly from the parasitoid life habit, such as some ichneumonoid wasps (Eggleton
and Belshaw 1992). Second, Hymenoptera parasitoid to phytophage transitions
occurred in several families that formerly fed on larvae in highly nutritious habitats
such as leaf mines and galls, the Cynipidae being the best example (Fergusson
1990). Third, transitions from egg parasitoidism to egg predation are documented in
Evaniidae (Askew 1971). Parasitoidism is a widespread life habit in Hymenoptera
that is a rich source of secondary predation and phytophagy.
11.6 Modern Food Webs and the Mid-Mesozoic Parasitoid
Revolution (MMPR)
Much of the ensuing discussion references Fig. 11.19, which documents the diversity of major parasitoid clades and groups from the time of their initial appearance
during the late Early Jurassic to their representation in the recent record. The fossil
diversity of seven major clades or groups of parasitoids—non-proctotrupomorph
Hymenoptera, proctotrupomorph Hymenoptera, aculeate Hymenoptera, noneremoneuran Diptera, eremoneuran Diptera, Strepsiptera and Coleoptera—record
first the establishment of the Mid-Mesozoic Parasitoid Revolution (MMPR) and
then the subsequent expansion of parasitoid groups and clades through time. Other
clades with rare parasitoid members—Neuroptera, Trichoptera and Lepidoptera—
each contain one or two families of parasitoid taxa that are not included because of
an insufficient or irrelevant fossil record. The MMPR is a time interval during the
late Early Jurassic to late Early Cretaceous (phases 1 and 2) in which bottom-to-top
regulation of terrestrial food webs dominated by inefficient clades of predators were
replaced by top-to-bottom trophic regulation by considerably more efficient parasitoid clades. After the MMPR, these clades subsequently expanded (phases 3 and 4)
as parasitoids became trophically entrenched in terrestrial food webs to the present
day. The initial pulse of the MMPR consisted of phases 1 and 2 that represented the
earliest occurrences and establishment of most parasitoid lineages in terrestrial habitats from the latest Early Jurassic (Toarcian Stage) to the Early Cretaceous (Albian
Stage). Commencing with the Late Cretaceous is the subsequent evolutionary diversification and ecological expansion of parasitoids represented by phases 3 and 4 that
continues to the present day.
C. C. Labandeira and L. Li