456
convergent on larvae of Ripiphoridae and Meloidae (Kathirithamby 2009) and frequently are confused with each other in the fossil record because of the structural
similarity (Beutel et al. 2016). As the triungulin larvae emerge from the female’s
body, they then consume her. The strepsipteran hypermetamorphic larva is a mobile,
hexapodous, host-seeking triungulin instar (Pohl and Beutel 2019), which immediately after burrowing through their host’s exocuticle molts into a second instar, a
featureless, vermiform individual. This vermiform larva induces the host to produce
a gall- like structure from which the larva feeds as it undergoes four more molts,
during which the host is castrated. Larval hosts of Strepsiptera include silverfish
(Thysanura), cockroaches (Blattodea), mole crickets (Orthoptera), planthoppers
and leafhoppers (Hemiptera–Auchenorrhyncha), and bees and wasps (Hymenoptera–
Aculeata) (Kathirithamby 2009). For Myrmecolacidae the larval host is different
from the host to which the female is embedded (Hayward et al. 2011). The unique
life cycle of Strepsiptera likely originated once. Recently, another distinctive hypermetamorphic stage of the strepsipteran life cycle was confirmed by discovery of the
first free-living, late-instar larva, probably a female, belonging to a stem-group lineage of Strepsiptera from 44 million-year-old middle Eocene Baltic Amber (Pohl
et al. 2019).
Considerable discussion has centered on whether strepsipterans, with the exception of the Mengenillidae, are parasites or parasitoids. Features mitigating against a
parasitoid designation are (1) the host does not typically die immediately after adult
emergence; (2) multiple females and multiple males can live within a single host;
and (3) the adults are parasitic and not the larvae (Kathirithamby 2009). Nevertheless,
Strepsiptera castrate their hosts, which renders them genetically dead, closely
resembling the standard parasitoid life habit. Additionally, the basal-most extant
lineage of Strepsiptera are the Mengeidae, which are considered true parasitoids,
indicating that the life habits of the other extant, likely derived families evolved
some morphological and behavioral features inconsistent with the ancestral parasitoid condition. Because of castration of their hosts and other nominal parasitoid
features, Strepsiptera are here considered as parasitoids. However, if a traditional
definition of parasitism in the Strepsiptera is accepted, in which host death is not
imminent upon emergence of the parasitoid, then the transition from Mengeidae to
other strepsipteran lineages could be construed as a shift from the parasitoid to a
parasite life habit.
Although mengeid strepsipterans are endoparasitoids of soil-dwelling silverfish,
Strepsiptera probably evolved from a Permian lineage of beetle taxa involved in
mycophagy and wood boring (Eggleton and Belshaw 1992). This is particularly
relevant since Strepsiptera likely are closely related to or the sister clade to
Coleoptera (Misof et al. 2014), and early beetles are associated with wood, such as
fungi-consuming polyphagan beetles in conifer host trees from the late Permian of
northern China (Feng et al. 2017). After an approximate 190 million-year-long
interval of a presumed divergence event from Coleoptera during the Early Permian,
early Strepsiptera consisted of three extinct clades. First is extinct “Protostrepsiptera”,
possessing plesiomorphic features and appearing in 99 million-year-old Myanmar
Amber (Grimaldi et al. 2005; Pohl et al. 2005; Kathirithamby and Engel 2014;
C. C. Labandeira and L. Li
convergent on larvae of Ripiphoridae and Meloidae (Kathirithamby 2009) and frequently are confused with each other in the fossil record because of the structural
similarity (Beutel et al. 2016). As the triungulin larvae emerge from the female’s
body, they then consume her. The strepsipteran hypermetamorphic larva is a mobile,
hexapodous, host-seeking triungulin instar (Pohl and Beutel 2019), which immediately after burrowing through their host’s exocuticle molts into a second instar, a
featureless, vermiform individual. This vermiform larva induces the host to produce
a gall- like structure from which the larva feeds as it undergoes four more molts,
during which the host is castrated. Larval hosts of Strepsiptera include silverfish
(Thysanura), cockroaches (Blattodea), mole crickets (Orthoptera), planthoppers
and leafhoppers (Hemiptera–Auchenorrhyncha), and bees and wasps (Hymenoptera–
Aculeata) (Kathirithamby 2009). For Myrmecolacidae the larval host is different
from the host to which the female is embedded (Hayward et al. 2011). The unique
life cycle of Strepsiptera likely originated once. Recently, another distinctive hypermetamorphic stage of the strepsipteran life cycle was confirmed by discovery of the
first free-living, late-instar larva, probably a female, belonging to a stem-group lineage of Strepsiptera from 44 million-year-old middle Eocene Baltic Amber (Pohl
et al. 2019).
Considerable discussion has centered on whether strepsipterans, with the exception of the Mengenillidae, are parasites or parasitoids. Features mitigating against a
parasitoid designation are (1) the host does not typically die immediately after adult
emergence; (2) multiple females and multiple males can live within a single host;
and (3) the adults are parasitic and not the larvae (Kathirithamby 2009). Nevertheless,
Strepsiptera castrate their hosts, which renders them genetically dead, closely
resembling the standard parasitoid life habit. Additionally, the basal-most extant
lineage of Strepsiptera are the Mengeidae, which are considered true parasitoids,
indicating that the life habits of the other extant, likely derived families evolved
some morphological and behavioral features inconsistent with the ancestral parasitoid condition. Because of castration of their hosts and other nominal parasitoid
features, Strepsiptera are here considered as parasitoids. However, if a traditional
definition of parasitism in the Strepsiptera is accepted, in which host death is not
imminent upon emergence of the parasitoid, then the transition from Mengeidae to
other strepsipteran lineages could be construed as a shift from the parasitoid to a
parasite life habit.
Although mengeid strepsipterans are endoparasitoids of soil-dwelling silverfish,
Strepsiptera probably evolved from a Permian lineage of beetle taxa involved in
mycophagy and wood boring (Eggleton and Belshaw 1992). This is particularly
relevant since Strepsiptera likely are closely related to or the sister clade to
Coleoptera (Misof et al. 2014), and early beetles are associated with wood, such as
fungi-consuming polyphagan beetles in conifer host trees from the late Permian of
northern China (Feng et al. 2017). After an approximate 190 million-year-long
interval of a presumed divergence event from Coleoptera during the Early Permian,
early Strepsiptera consisted of three extinct clades. First is extinct “Protostrepsiptera”,
possessing plesiomorphic features and appearing in 99 million-year-old Myanmar
Amber (Grimaldi et al. 2005; Pohl et al. 2005; Kathirithamby and Engel 2014;
C. C. Labandeira and L. Li