Genetic diversity, reproductive systems and endosymbionts of two invasive thrips species

Abstract

The majority of insect species reproduce sexually while some can reproduce asexually. In most cases, the genetic basis for this and for sex determination sits in insect genomes, while other factors can also play a role. For example sex determination and sex ratio can be manipulated by the endosymbiotic bacteria Cardinium (Phylum: Bacteroidetes))and Wolbachia (Phylum: Proteobacteria) that reside in the cytoplasm of host cells. These maternally inherited bacteria can manipulate host reproduction by mechanisms such as cytoplasmic incompatibility (CI), thelytokous parthenogenesis, male killing and feminisation, and this can lead to distortion of host sex ratio. Endosymbionts and their roles as sex ratio distorters have been studied intensively in many insect orders. Thysanoptera is one of two insect orders in which the majority of taxa reproduce by arrhenotokous haplodiploidy with the remaining reproducing by thelytoky. Thus far, the influence of endosymbionts in thrips sex determination and sex ratio has received very little attention, except for the report of Wolbachia induced thelytoky in less than a handful of thrips species. Wolbachia has also been detected in some arrhenotokous thrips but the role of this bacterium in their reproduction has not been characterised. This PhD project was undertaken to expand the knowledge of the role of bacterial endosymbionts as sex ratio distorters in asexual and sexual reproduction of two representative species of the order Thysanoptera. Thelytokous Heliothrips haemorrhoidalis (Bouche') (Thysanoptera: Thripidae) and arrhenotokous Pezothrips kellyanus (Bagnall) (Thysanoptera: Thripidae) were selected as the target species due to their different reproductive systems and their status as significant horticultural pests. Genetic and symbiont diversity of these two species were also studied and characterised with the aim to identify their geographical origin.

Date of Award	2015
Original language	English