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M.Sc. thesis

» The complexes and genetic diversity of aphidiines (Hymenoptera: Braconidae) on non-crop plants

A thesis submitted in partial fulfilment of the requirements for the degree of Master of Science, 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.

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.

Ph.D. thesis

» Inducible honey bee viruses associated with Varroa jacobsoni

Thesis submitted for the degree of Doctor of Philosophy, 1999. Department of Entomology & Nematology, IACR-Rothamsted, Hertfordshire, UK and School of Life Sciences, Keele University, Staffordshire, UK.

Acute paralysis virus (APV) and slow paralysis virus (SPV) are only known to cause mortality of European honey bees, Apis mellifera L. (Hymenoptera: Apidae), in colonies infested with Varroa jacobsoni Oudemans (Acari: Varroidae). The hypothesis that this parasitic mite can induce inapparent, sublethal virus infections to become overt and lethal was tested by subjecting bees to treatments that mimicked mite feeding. Direct evidence of mite-mediated virus induction was not obtained due to difficulties in obtaining virus-free mites. APV and SPV were found to be inducible in both adult and pupal honey bees in the laboratory by the injection of apyrase, an enzyme common to the saliva of many haematophagous arthropods, suggesting that V. jacobsoni saliva contains virus-inducing substances; physical stimuli were unsuccessful. The proportion of inducible infections of both viruses in adult honey bees was found to peak during the brood-rearing season and both viruses could be induced in the same individual. There is some evidence that virus induction is more easily achieved in parasitised bees. However, experiments that attempted to separate the effects of virus inducing stimuli from the physiological state of the individual were unsuccessful. The injection of relatively large volumes of potassium phosphate buffer achieved 100% APV induction in pupae. The humoral response of adult honey bees to the injection of APV or mite parasitism appears to be an activation of the phenoloxidase system. APV infection appears to inhibit the production of antimicrobial peptides. The injection of potassium phosphate buffer or apyrase induced the synthesis of such peptides, but neither activated the phenoloxidase system. Using infectivity tests, APV displayed significant intercolony variation and both APV and SPV showed intracolony variation. SPV shows less tissue specificity that APV. Both viruses can be found in tissues concerned with oral secretion, suggesting an oral route of normal transmission.

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