Abstract
Vespula wasps V. vulgaris and V. germanica are an extremely invasive pest in New Zealand. New Zealand boasts the highest densities of these species globally, with annual economic damages estimates at NZD $133 million. Their domination of honeydew produced by scale insects in native beech forests is to the detriment of native birds, and their consumption of native invertebrates results in a virtually zero percent chance of survival for some species in beech forests during wasp season.
A reduction of at least 80% of wasp densities is required to reverse these damages. Current efforts to manage these wasps involve the use of the insecticide Vespex®, containing fipronil. While Vespex® can reduce wasp densities at an average of 95%, intensive, unfeasible labour requirements would be necessary to achieve the same results in beech forests.
This thesis aimed to explore new genetic techniques RNA interference (RNAi) and Receptor-Mediated Ovary Transduction of Cargo (ReMOT Control), to create a species-specific method for controlling V. vulgaris populations in New Zealand. RNA interference (RNAi) acts as a species-specific poison, silencing the expression of selected genes. I initially evaluated the potential of several candidate reference genes to ensure robust reference genes were selected for accurate RNAi analysis. Analyses resulted in the selection of four of the most stable reference genes. Progressing from a thorough reference gene selection to RNAi experiments, I have shown that feeding and injection applications of RNA interference are not effective tools for wasp control, as no significant changes in gene expression were observed with the feeding or injection of dsRNAs for three different genes across larvae, pupae and adults.
A relatively new technique, ReMOT Control, is an extension of CRISPR-Cas9 gene editing that circumvents the need to inject pre-blastoderm embryos before they divide. This technique is more appealing than traditional CRISPR approaches, as Vespula wasps are seasonal, non-model organisms, making injection of freshly laid embryos almost impossible. When exploring the potential of ReMOT Control CRISPR gene editing, I found uptake of the majority of the P2C ligands derived from Drosophila yolk proteins in V. vulgaris worker ovaries, highlighting the potential of this technique for effective gene editing in reproductive V. vulgaris females.
This work also aimed to develop a better protocol for rearing wasps in a laboratory setting, and visualise life stages and ovary development of workers in comparison to queen individuals. For this, I photographed individuals from all life stages in a gradual progression, and also worker ovaries ranging from no to full activation in the absence of a queen. Nest boxes for adults to reside in post experiments were designed, along with effective boxes to rear larvae to adulthood. The presence of genes Vasa and oskar were observed via hybridisation chain reaction (HCR) in worker ovaries, showing the presence of these genes are essential for reproduction and differing from honeybee Apis mellifera ovary composition.
This thesis also delved into the venome of V. vulgaris via mass spectrometry, uncovering a number of venom peptides not described yet in this species. I also considered whether particular venom peptides were a factor in the invasiveness, and compared my data across 25 hymenopteran genomes. I found several proteins that were present in all genomes, but no evidence that any venom proteins were exclusively present in invasive or eusocial species. Two proteins were absent from both V. germanica and V. pensylvanica genomes, and should be explored further.
Overall, this thesis has discredited one genetic method for effective wasp control, and highlighted the potential of another. Additional areas concerning V. vulgaris’ biology have been unveiled, improving our understanding of this species.