DISSCUSSION ON THE STUDY OF PHYLOGENY OF STREPSIPTERA
GE Si-Qin, YANG Xing-Ke, CUI Jun-Zhi, LI Wen-Zhu Institute of Zoology, Chinese Academy of Sciences, Beijing 100080
This paper mainly discusses the phylogeny of the Strepsiptera including, the taxonomic characteristics, phylogenetic placement, origin and phylogeny of this family. The Strepsiptera are obligate parasites of other insects, with a range of hosts from 7 orders and 34 families. They are an odd group of insects whose phylogenetic relationships have long been a mystery. Females are wingless, and in all families, except the Mengenillidae, are highly modified and reduced, without appendages, never leaving the host. Males have many derived features as well, including reduced forewings, fan-shaped hindwings, antennae with processes, and unusual raspberry-like eyes. In recent years, four phylogenetic placements of the Strepsiptera have been discussed: 1) Sister group to the Endopterygota;2)Sister group to the Rhipiphoridae;3)Sister group to the Coleoptera; 4) Sister group to the Diptera. Though the taxonomic position of the Strepsiptera is still not resolved, molecular and morphological research currently in progress should clarify the position of this group. The oldest Strepsipteran fossil is a first instar larval Stichotrema eocaenicum (Haupt, 1950) from the Eocene period found in Germany. After Kinzelbach's research, most living genera were probably extant through most of the Tertiary. According to Kathinthamby's hypotheses, the Myrmecolacidae may have appeared in the late Cretaceous, and the Halictophagidae, Elenchidae, Corixenidae and Mengenillidae perhaps had an origin in the Jurassic. However, if the Coleoptera are indeed the sister group of the Strepsiptera, this suggests an even older origin. Coleopteran fossils extend to the Permian, and, based on sister-group dating, the Strepsiptera should also be expected to be this old, however, the oldest Strepsipteran fossil is from Eocene. Consequently, a sister-group relationship with the Coleoptera is unlikely in the absence of further evidence. The Strepsiptera is divided into two suborders (Mengeillidia and Stylopidia) and nine families. The monophyly of the Stylopidia has been confirmed but that of the Mengeillidia is unconfirmed. The Mengeillidia has two families, but the Mengidae is known only from a few fossil males and shares many plesiomorphic characters with the Mengenillidae. Consequently, the two groups have often been associated with one another. Hence the phylogenetic position of the Mengeidae will remain uncertain until additional specimens are found which allow a more detailed analysis of the morphology and life history of the Mengidae.