470
11.6.1 Ovipositors and Host-Seeking First Instar Larvae:
Vetting the Parasitoid Taxa
Among the seven parasitoid clades and groups (Fig. 11.19), evidence for parasitoidism is excellent for non-proctotrupomorph and proctotrupomorph Hymenoptera as
well as non-eremoneuran and eremoneuran Diptera. For these four groups, the near
certainty of their parasitoid status is attributable to presence of a distinctive female
ovipositor or oviscapt whose structure is designed to deposit eggs in or on their
arthropod or non-arthropod hosts (Askew 1971). The oviposition of eggs often is
accomplished by long ovipositors penetrating through considerable distances or
thicknesses of intervening tissue, such as wood in the case of ichneumonid wasps
targeting wood-boring larvae through several centimeters of wood (Clausen 1940;
Gauld 2008). A second type of evidence is the presence of a highly ambulatory,
host-seeking triungulin larva that forms the first larval instar of some Neuroptera,
Strepsiptera and Coleoptera, particularly Mantispidae, Ripiphoridae, Meloidae,
Bothriderinae of Bothrideridae and all strepsipteran clades, a feature that almost
assures a parasitoid designation (Crowson 1981; Evans and Steury 2012). An analogous host-seeking larva, the planidium, exists for many parasitoid Diptera, for
example, Mycetophilidae, Nemestrinidae, Acroceridae, Asilidae and Rhinophoridae,
that also represents parasitoid status (Eggleton and Belshaw 1992). The confidence
level is somewhat lowered for aculeate Hymenoptera, as their ovipositor is modified
for stinging and paralyzing prey, rather than necessarily for ovipositing eggs in or
on their prey (Gauld and Bolton 1988; Whitfield 2003). However, knowledge of the
life histories and biology of modern parasitoid aculeate Hymenoptera provides considerable evidence for assigning an aculeate Hymenoptera fossil species to a predator, parasite or parasitoid. In the case of all fossil Rhipiceridae and all Passandridae
(Coleoptera), an assignment to parasitoid status is highly probable, owing to the
condition that the modern families are depauperate clades that only possess the
single life habit of parasitoidism.
The weakest case for a parasitoid assignment are the remaining, highly speciose
families of Carabidae, Staphylinidae and Cleridae in Coleoptera, each of which
overall is sparsely represented by extant parasitoid taxa. Depending on the subfamily structure of the fossil occurrences and other parasitoid-relevant information for
these three beetle families, a judgement was made regarding whether parasitoids
were present for a given lineage occurring in a particular geological stage. For
example, nearly all modern parasitoid taxa in Staphylinidae are from Subfamily
Aleocharinae (Maus et al. 1998), a subgroup that only extends to the Cenomanian
(Cai and Huang 2014; Yamamoto et al. 2016). Parasitoid assignments to
Staphylinidae were not made in the absence of Aleocharinae for pre-Cenomanian
occurrences and in lieu of evidence for the presence of Aleocharinae only in more
recent occurrences. While the full range of parasitoid-bearing families listed in
Table 11.1 provides the data for Fig. 11.19, determination of parasitoid presence in
the fossil record was more circumspect in the narratives for Sects. 11.6.4–11.6.6
below. It is for this lack of trophic specificity, the lack of evidence from the fossil
C. C. Labandeira and L. Li
11.6.1 Ovipositors and Host-Seeking First Instar Larvae:
Vetting the Parasitoid Taxa
Among the seven parasitoid clades and groups (Fig. 11.19), evidence for parasitoidism is excellent for non-proctotrupomorph and proctotrupomorph Hymenoptera as
well as non-eremoneuran and eremoneuran Diptera. For these four groups, the near
certainty of their parasitoid status is attributable to presence of a distinctive female
ovipositor or oviscapt whose structure is designed to deposit eggs in or on their
arthropod or non-arthropod hosts (Askew 1971). The oviposition of eggs often is
accomplished by long ovipositors penetrating through considerable distances or
thicknesses of intervening tissue, such as wood in the case of ichneumonid wasps
targeting wood-boring larvae through several centimeters of wood (Clausen 1940;
Gauld 2008). A second type of evidence is the presence of a highly ambulatory,
host-seeking triungulin larva that forms the first larval instar of some Neuroptera,
Strepsiptera and Coleoptera, particularly Mantispidae, Ripiphoridae, Meloidae,
Bothriderinae of Bothrideridae and all strepsipteran clades, a feature that almost
assures a parasitoid designation (Crowson 1981; Evans and Steury 2012). An analogous host-seeking larva, the planidium, exists for many parasitoid Diptera, for
example, Mycetophilidae, Nemestrinidae, Acroceridae, Asilidae and Rhinophoridae,
that also represents parasitoid status (Eggleton and Belshaw 1992). The confidence
level is somewhat lowered for aculeate Hymenoptera, as their ovipositor is modified
for stinging and paralyzing prey, rather than necessarily for ovipositing eggs in or
on their prey (Gauld and Bolton 1988; Whitfield 2003). However, knowledge of the
life histories and biology of modern parasitoid aculeate Hymenoptera provides considerable evidence for assigning an aculeate Hymenoptera fossil species to a predator, parasite or parasitoid. In the case of all fossil Rhipiceridae and all Passandridae
(Coleoptera), an assignment to parasitoid status is highly probable, owing to the
condition that the modern families are depauperate clades that only possess the
single life habit of parasitoidism.
The weakest case for a parasitoid assignment are the remaining, highly speciose
families of Carabidae, Staphylinidae and Cleridae in Coleoptera, each of which
overall is sparsely represented by extant parasitoid taxa. Depending on the subfamily structure of the fossil occurrences and other parasitoid-relevant information for
these three beetle families, a judgement was made regarding whether parasitoids
were present for a given lineage occurring in a particular geological stage. For
example, nearly all modern parasitoid taxa in Staphylinidae are from Subfamily
Aleocharinae (Maus et al. 1998), a subgroup that only extends to the Cenomanian
(Cai and Huang 2014; Yamamoto et al. 2016). Parasitoid assignments to
Staphylinidae were not made in the absence of Aleocharinae for pre-Cenomanian
occurrences and in lieu of evidence for the presence of Aleocharinae only in more
recent occurrences. While the full range of parasitoid-bearing families listed in
Table 11.1 provides the data for Fig. 11.19, determination of parasitoid presence in
the fossil record was more circumspect in the narratives for Sects. 11.6.4–11.6.6
below. It is for this lack of trophic specificity, the lack of evidence from the fossil
C. C. Labandeira and L. Li