Reproductive biology, ultrastructure and molecular characterisation of Liposcelis bostrychophila (Badonnel) (Liposcelididae: Psocoptera) and its intracellular rickettsial endosymbionts

The psocid Liposcelis bostrychophila is a stored product pest and has an interesting and complex reproductiv biology. However information available on this insect is rather limited. This thesis describes the gross morphology, anatomy of the reproductive organs of L. bostrychophila and to a lesser extent the digestive system, using serially sectioned materials for light microscopy. This study also involves an investigation of the fine ultrastructural details of the reproductive organs of adults and their developing juveniles. boti#hephilas oocyte and-oogenor,is were also studied. The electron microscope (EM) pictures of the ultrastructure of psocid gonads revealed the presence of endosymbiotic rickettsiae belonging to the a-proteobacteria. The implications of the presence/absence, location, mode of transmission and the ultrastructure of the Rickettsia-like organisms (RLO) found to inhabit in the ovaries and other specialised sub-cutaneous structures in this psocidoveexplored. Transovarial transmission of these bacteria has been also established, by conducting egg-embryo, juvenile and adult ultrastructural evidence using EM. The standard technique of demonstrating the significance and the possible role of these endosymbiontsrelationship with the host consists of eliminating the microrganisms, resultinØ' cteria-free individuals termed aposymbiotic. To achieve this a range of antibiotic and heat treatments were employed. One antibiotic (nfampicin) produced aposymbiotic individuals, whilst the prolonged and repeated exposure of high temperature and tetracycline achieved a gradual decontamination of the psocid infection as validated by EM micrographs. The nature of the L. bostiychophila rickettsial endosymbionts were further characterised using PCR to amplify the 16S r-RNA, a widely recognised and conserved bacterial gene. The PCR product was characterised using restriction and sequence analysis. This provided the genetic characterisation, phylogenetic and nucleotide variation analysis of bacterial endosymbionts, without the necessity of culturing the bacteria independently of the host. The sample sequence wcompared With the bacterial genome database, the sample sequence was seen to be most similar to those from the rickettsias and their relatives. There was 97.6% similarity in the nucleotide sequence from the liposcelid isolates and intracellular parasitic bacteria found in many other insects. And finally the variability in egg production of L. bosirychophila populations from different locations in the UK was quantified. These populations represented a sample of the variability that allows this insect to become established and exploit a wide range of habitats. The relationship between the variation in egg production of these populations (30) and bacterial load were explored. Different population of L. bosirychophila were found to harbour different bacterial loads. This two factors were found to negatively correlate. The interaction and influence of bacterial density on the overall fitness and survivorship of different populations of L. bostrychophila is studied.