A thesis submitted in partial fulfilment of the requirements for the MSc degree of the University of London and the Diploma of Imperial College. Department of Pure and Applied Biology, Imperial College of Science, Technology and Medicine, Silwood Park, Ascot, Berkshire, UK. September 1994.
All figures are copyright Colin Denholm unless stated otherwise. This online thesis is comprehensively cross-referenced using the contents section below.
Materials and methods
The composition of the parasite complex of the common nettle aphid (Microlophium carnosum) was investigated. The primary parasites were Aphidius microlophii, and A. urticae. Hyperparasites reared were Dendrocerus carpenteri, Alloxysta victrix, Coruna clavata and Asaphes vulgaris. The composition of the complex was shown to change significantly from year to year and between patches. A. microlophii tripled its relative abundance from 1993 and 1994, while A. urticae dropped from constituting 14% of the complex in 1993 to 4.2% in 1994. As. vulgaris was found to be significantly more abundant in one patch than in any other, with the other parasites having roughly equal representation in all patches. The mean time for emergence after collection was calculated for each species. The primary parasites emerged up to five days earlier than the hyperparasites. A protocol for cellulose acetate electrophoresis was developed. Useful buffers were 0.1M tris-maleate pH=7.8 and 0.05M tris-citrate pH=7.8. Low melting point agarose was found to be a convenient substitute for bacterial grade agar used in the staining procedure. Of the twenty enzymes tested, eight could be scored in the aphidiines examined. These constitute ten loci. A new plant-aphid record is described for Lysiphlebus cardui Marshall. The genetic diversity of two subpopulations of L. cardui was investigated. L. cardui ex ragwort (Senecio jacobaea) and L. cardui ex creeping thistle (Cirsium arvense) were found to be genetically very similar, with Nei's coefficient of genetic identity (Ij) calculated as 0.99996. The overall heterozygosity was exceptionally low for the ten loci examined. L. cardui in Silwood Park appears to be thelytokous and consist of two clonal lineages. Both clones were equally represented on both plants. Isoenzyme comparisons were conducted between L. cardui and A. urticae and L. cardui and A. smithi collected from broom (Cytisus scoparius). L. cardui can be distinguished from A. urticae at the PGI and PGM loci, and from A. smithi at the PGI locus.
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