Browsing by Person "Wagener, Barbara"

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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.