PhD project

Project 2 Behavioural manipulation and co-evolutionary processes between fungi and flies (DK)

The expanding industry of insect mass rearing aims to produce millions of insects that provide beneficial services to humankind, such as biocontrol agents, animal feed and human food. However, this intensive production system also incurs potential insect health consequences from rearing at such high densities. This developing industry is already facing disease outbreaks in their insect cultures from insect-pathogenic bacteria, viruses, fungi, and other pathogens.

Some entomopathogenic parasites, notably fungi, can take over and manipulate the behaviour of infected insects for their own benefit, turning their hosts into “zombies”. These behavioural manipulations often increase fungal transmission to new susceptible hosts, and contribute to the epizootic capacity of the pathogen. This project aims to determine pathogen beneficial host manipulation by Entomophthora muscae in houseflies (Musca domestica) and by insect-infecting microsporidia. Additionally, houseflies are natural vectors of >100 different bacterial and viral food-borne human diseases, and like a number of other insect hosts suffering from microsporidia infection, are mass-reared in feed production, thus stressing the importance of understanding infection mechanisms.

During the final stages of a ~six-day infection from the exposure to infective E. muscae conidia, the obligate parasitic fungus manipulates its housefly host to perform a sequence of characteristic behaviours. The pathogenic fungus rings down the infection curtain by puppeteering its host in the following steps: 1) climb to an elevated position, 2) affix its proboscis to the substrate, 3) bow with raised wings and finally 4) die. This sequential performance is the curtain call of the infection. Following death, the fungus then erupts through the intersegmental membrane of the abdomen to sporulate (see photo 1).

The mechanisms involved in the fungal puppeteer’s manipulation of houseflies are unknown. To uncover these mechanisms, I will characterise and collect detailed information on the behaviour alterations visible in the insect host. Having characterised the intricacies of the manipulated behaviours, the aim now is to align what is occurring at a molecular level to allow for these manipulations. At the University of Copenhagen, I have optimised a RNA extraction protocol for extracting high-quality total RNA from fly heads to uncover the genes and molecules secreted by E. muscae during the conversion of these manipulations. I will use dual RNAseq on infected fly heads to discover what is expressed in the brain during manipulation.

This optimisation of RNA extraction from fungus-infected insects will also form the foundation for the second major goal of this project, based at the University of Exeter, involving microsporidia modification of host metabolites and homeostatic levels. Ultimately, I want the project to culminate in identifying co-evolutionary mechanisms of infection by my two pathogens.