Browsing by Subject "Hymenoptera"

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Integrative taxonomy of platygastrine wasps of Germany
(2023) Awad, Jessica; Krogmann, Lars
In the context of the sixth mass extinction, our understanding of insect decline is severely limited by a lack of information on biodiversity. Many highly abundant and diverse insect groups remain unidentifiable to species or even to genus. The parasitoid wasp superfamily Platygastroidea is one such “dark taxon”. The taxonomic impediment is especially severe in the Palearctic Platygastrinae due to the proliferation of names with vague concepts. Platygastrine wasps parasitize the hyper-diverse Cecidomyiidae (Diptera), suggesting that their species richness may be correspondingly high. Revisionary work is needed to identify named species and to discover new ones. This work applies integrative taxonomic methods to address the most pressing problems within the subfamily. The research presented in this dissertation focuses on Europe, particularly Germany, which is the current center of insect decline research as well as a historical center of platygastrine taxonomy. As part of this work, historical descriptions and their associated type material were examined and clarified so that further revisionary work can occur. The dissertation is structured in five chapters, of which two are published and three are unpublished. The first chapter reviews 18 genera of Platygastridae described by Arnold Förster (1856), most of which represent distinct and recognizable lineages. The study provides their taxonomic history, diagnostic remarks, English translations, and illustrations of important specimens from the Förster collection in the Natural History Museum Vienna. The collection also includes original exemplar specimens of European species whose types have been lost. Potential neotypes and lectotypes from this material are noted, with the aim of improving nomenclatural stability in the group. Potential neotypes were found for Amblyaspis forticornis (Nees, 1834), Isocybus grandis (Nees, 1834), Platygaster striolata Nees, 1834, and Trichacis tristis (Nees, 1834). Lectotypes will be designated for Platygaster spinigera Nees, 1834, which will be transferred to Leptacis, and for Platygaster corvina Förster, 1861, with Platygaster henkvlugi Buhl, 1996 treated as a junior synonym. Synopeas mutica (Nees, 1834) should be transferred back to Platygaster. The second chapter addresses generic concepts within Platygastrinae sensu Ashmead. Part of Platygastrinae (former Inostemmatinae sensu Ashmead) was reviewed and keyed by Masner & Huggert (1989). However, more than half of the genera in the subfamily, including the vast majority of species, have not been revised. A working key to 14 major world genera, the first of its kind, is provided. An additional six genera and three subgenera of uncertain placement are discussed. The third chapter focuses on nomenclatural problems in the genus Platygaster Latreille, which is the type genus for its subfamily, family, and superfamily. It is also the largest genus in Platygastroidea with nearly 700 species, and recent evidence indicates that it is not monophyletic. It is necessary to establish the identity of the type specimen, as well as the identities of the 13 generic junior synonyms and four subgenera, in order to proceed with taxonomic divisions. The type specimen Scelio ruficornis Latreille, 1805, lost to science for 192 years, was rediscovered. However, it does not belong to the prevailing concept of Platygaster, but to Isocybus Förster, which has extreme taxonomic ramifications. The proposed solution would replace the type species of each genus in order to retain prevailing usage and prevent widespread confusion. A petition is presented to designate Epimeces ensifer Westwood as the type of Platygaster and Scelio ruficornis as the type of Isocybus. In the fourth chapter, the genus Trichacis Förster is revised for Europe. Examination of historical and modern collections combined with DNA barcoding revealed the presence of only a single species in Europe, Trichacis tristis (Nees, 1834), redescribed here. The results suggest that T. tristis has 14 junior synonyms: T. abdominalis (Thomson, 1859); T. bidentiscutum Szabó, 1981; T. didas (Walker, 1835); T. fusciala Szabó, 1981; T. hajduica Szabó, 1981; T. illusor Kieffer, 1916; T. nosferatus Buhl, 1997; T. pisis (Walker, 1835); T. persicus Asadi & Buhl, 2021; T. pulchricornis Szelényi, 1953; T. quadriclava Szabó, 1981; T. remulus (Walker, 1835); T. vitreus Buhl, 1997; and T. weiperti Buhl, 2019. Four species should be transferred to Amblyaspis Förster: T. afurcata Szabó, 1977, T. hungarica Szabó, 1977, T. pannonica Szabó, 1977, and T. tatika Szabó, 1977. Intraspecific variation, biological associations, and taxonomic history are discussed. DNA barcodes are provided and analyzed in the context of worldwide Trichacis and its sister genus Isocybus Förster. The fifth chapter examines platygastrid diversity in Germany in the context of insect decline. DNA barcodes indicate the presence of 178 observed species, with an estimated total of 290. GBOL sampling captured an estimated 93.7% of total species richness, but only 45.8% of rare species. A case study from Isocybus compares historical specimens, DNA barcode vouchers, and ecological data to illustrate the possible decline of a wetland parasitoid species. Altogether, the research demonstrates the importance of historical material, especially type specimens, in understanding biodiversity through time, and provides an essential taxonomic foundation for much-needed modern identification resources for Platygastrinae in the western Palearctic and beyond.
Molecular systematics of selected Diadegma species (Hymenoptera: Ichneumonidae: Campoplegine) important in biological control
(2006) Wagener, Barbara; Zebitz, Claus P. W.
The genus Diadegma (Hymenoptera: Ichneumonidae: Campopleginae) represents a large group of parasitoids with 201 species worldwide. Adult Diadegma females parasitise larvae of various lepidopteran species and some species, in particular Diadegma insulare (Cresson) and D. semiclausum (Hellén), have gained economic importance as biological control agents of Plutella xylostella (Linnaeus). A low parasitism rate of <15 % of the parasitoid complex (Diadegma sp., Oomyces sokolowskii (Kurdjumov) and Diaplazon laetatorius (Fabricius)) in unsprayed cabbage and kale fields infested with P. xylostella in eastern and southern Africa was the starting point for the development of a biological control project for P. xylostella which was implemented by the International Centre of Insect Physiology and Ecology (ICIPE), Kenya. One of the objectives of the biocontrol project was to examine the taxonomic status of Diadegma species associated with P. xylostella in eastern and southern Africa and the exotic parasitoid D. semiclausum imported to Kenya from Taiwan (Asian Vegetable Research and Development Centre, AVRDC) by cross breeding experiments and molecular methods. Thus, two different molecular regions, a fragment of the mitochondrial cytochrome c oxidase subunit (COI) and the second internal transcribed spacer (ITS2) of ribosomal DNA were amplified utilising polymerase chain reaction (PCR) and digested afterwards with several restriction enzymes (PCR-Restriction Fragment Length Polymorphism-RFLP). In the due course of the study examinations of several Diadegma species attacking P. xylostella were undertaken with the PCR-RFLP method developed previously for the African Diadegma. This molecular method could solve some taxonomic difficulties of the genus Diadegma. Sequence analyses were used to investigate the phylogenetic relationship of nine Diadegma species (D. blackburni (Cameron), D. insulare, D. leontiniae (Brèthes), D. chrysostictos (Gmelin), D. armillata (Gravenhorst), D. fenestrale (Holmgren), D. mollipla (Holmgren), D. semiclausum, D. rapi (Cameron)) and the phylogenetic relationship of the genus Diadegma within the superfamily Ichneumonoidea. Cross breeding experiments were carried out between two populations of D. mollipla from eastern and southern Africa. No significant differences in the total number of progeny per female and the number of male offspring were obtained, whereas the female progeny showed significant differences. Hybrid females resulting from both reciprocal crosses were reproductively compatible with males of both parental lines, which indicated that no genetic incompatibility was apparent between the two D. mollipla populations. In contrast, crosses between D. mollipla and D. semiclausum resulted only in the occurrence of male offspring, which is typical for unfertilised progeny in Diadegma. The laboratory cultures of D. mollipla and D. semiclausum were highly male biased. Inbreeding, where homozygosity is much higher, is leading to a higher diploid male production. Diploid males can easily be detected by isoenzyme variations as a genetic marker. Heterozygote females/males of D. semiclausum and D. mollipla were identified by phosphoglucomutase (PGM) electrophoretic banding patterns. Crosses between a mother (heterozygote, diploid) and her son (homozygote, haploid) resulted in one diploid male in D. mollipla and none in D. semiclausum. Information about diploid males in D. semiclausum detected with PGM has already been published and different methodologies might be the reason why in D. semiclausum no diploid male was detected. Therefore the present analyses with PGM as molecular marker should be seen as a preliminary study.
New species based on the biological species concept within the complex of Lariophagus distinguendus (Hymenoptera, Chalcidoidea, Pteromalidae), a parasitoid of household pests
(2023) Pollmann, Marie; Kuhn, Denise; König, Christian; Homolka, Irmela; Paschke, Sina; Reinisch, Ronja; Schmidt, Anna; Schwabe, Noa; Weber, Justus; Gottlieb, Yuval; Steidle, Johannes Luitpold Maria
The pteromalid parasitoid Lariophagus distinguendus (Foerster) belongs to the Hymenoptera, a megadiverse insect order with high cryptic diversity. It attacks stored product pest beetles in human storage facilities. Recently, it has been shown to consist of two separate species. To further study its cryptic diversity, strains were collected to compare their relatedness using barcoding and nuclear genes. Nuclear genes identified two clusters which agree with the known two species, whereas the barcode fragment determined an additional third Clade. Total reproductive isolation (RI) according to the biological species concept (BSC) was investigated in crossing experiments within and between clusters using representative strains. Sexual isolation exists between all studied pairs, increasing from slight to strong with genetic distance. Postzygotic barriers mostly affected hybrid males, pointing to Haldane's rule. Hybrid females were only affected by unidirectional Spiroplasma‐induced cytoplasmic incompatibility and behavioural sterility, each in one specific strain combination. RI was virtually absent between strains separated by up to 2.8% COI difference, but strong or complete in three pairs from one Clade each, separated by at least 7.2%. Apparently, each of these clusters represents one separate species according to the BSC, highlighting cryptic diversity in direct vicinity to humans. In addition, these results challenge the recent ‘turbo‐taxonomy’ practice of using 2% COI differences to delimitate species, especially within parasitic Hymenoptera. The gradual increase in number and strength of reproductive barriers between strains with increasing genetic distance also sheds light on the emergence of barriers during the speciation process in L. distinguendus.