Classification after Kinzelbach (1971)
The Stylopidia are obligate parasites of other insects. This group is distinguished from the other suborder of Strepsiptera, the Mengenillidia, by the females, which are totally endoparasitic in their hosts. The Stylopidia is the larger of the two suborders, comprising 7 families and 584 species described so far.
The female Stylopidia possess no external characters typical for normal adult insects, such as eyes, antennae, mouthparts, legs, wings and external genitalia. The only visible feature is the cephalothorax, that extrudes through the host at the neotenic adult stage (fig. 1). The free-living male (fig. 2) emerges from the puparium in the host (fig. 3) and seeks an endoparasitic female and fertilizes it (fig. 4). The extreme sexual dimorphism is most pronounced in this suborder. In the suborder Mengenillidia, both the males and females emerge from the host to pupate externally. For more information on the insects parasitized by stylopidians see the page on Stylopidia Host Relationships.
Most stylopidian families are cosmopolitan in distribution. The only exceptions are:
- Callipharixenidae: now only known from South East Asia (Kinzelbach 1971, Kathirithamby unpublished)
- Bohartillidae: known from the Neotropics (Honduras and Ecuador, Kinzelbach 1969b and Kathirithamby unpublished) and in Dominican amber (Kathirithamby & Grimaldi 1993, Kinzelbach & Pohl 1994)
The autapomorphic characters of the suborder Stylopidia are:
- Neotenic females are totally endoparasitic in the hosts (fig. 1), unlike the Mengenillidia, which emerge during the last larval instar to pupate externally.
- Female Stylopidia have a number of genital openings from the body cavity into the apron.
- MA1 vein in the wing of male with only residues.
The suborder Stylopidia is distinct from the Mengenillidia, in that the females are totally endoparasitic in their hosts, and remain within their larval cuticles, except for the extruded cephalothorax. They do not undergo a pupal stage but become neotenic adults after the IVth larval stage, when the cephalothorax is extruded. The ventral surface (fig. 5) has a peritrophic matrix (fig. 6) that is analagous to the gut in insects and is referred to as the "brood canal/apron" (Kathirithamby 2000). Several genital tubes open from the body cavity of the female into the apron (fig. 7). The brood canal/apron is initially used for the entry of sperm and later as a passage to the outside for the emergence of the viviparous host-seeking 1st instar larvae from the body cavity of the mother to the outside (fig. 8).
Discussion of Phylogenetic Relationships
There are 7 families in this suborder, but many of the families are described only from females or males such as the females of Bohartillidae and males of Callipharixenidae are unknown, and only six females out of the 106 described Myrmecolacidae are known. Most of the species in the family Myrmecolacidae have been described from free-living males that have come into traps.
While the relationships among stylopidian families are largely unresolved, preliminary evidence indicates a sistergroup relationship between the Myrmecolacidae and Elenchidae. Autapomorphies that distinguish these two groups from the rest of the families are (Kinzelbach 1971):
- Narrow antennal joints
- Short female cephalothorax
- 2-4 genital openings in the female
- Wide brood canal opening
- Mesothoracic tarsus of 1st instar larva pointed
The sister group relationship is also seen in the analysis by Halbert et al. (2001) where seven Myrmecolacidae were compared to Elenchidae and Stylopidae. However, Pohl (2002), who studied the 1st instar larvae, does not support this sister group relationship. A phylogenetic analysis of the molecular data, which is at present being gathered would clarify this question.
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- First online 20 March 2003
Citing this page:
Kathirithamby, Jeyaraney. 2003. Stylopidia. Version 20 March 2003. http://tolweb.org/Stylopidia/14510/2003.03.20 in The Tree of Life Web Project, http://tolweb.org/