Research
I’m passionate about how viruses shape the world around us, specifically those that are beneficial to their hosts!
Insects called parasitoid wasps often rely on these ‘good’ viruses for their survival as parasites of other insects. Viruses are used as biological weapons by parasitoid wasps to incapacitate their hosts and allow the developing wasps to feed on hosts from the inside out.
My research focuses on characterizing these viruses to understand how mutualistic viruses arise and how they may lead to innovative strategies for controlling agricultural pests. Read on for descriptions of some of my current research projects.
Function of a Novel Symbiotic Poxvirus
A major part of my research to date has focused on characterization of a novel poxvirus described within the fruit fly-attacking parasitoid wasp Diachasmimorpha longicaudata. This virus, known as Diachasmimorpha longicaudata entomopoxvirus (DlEPV), is localized in the venom gland of female wasps and is injected into fruit fly larvae during wasp egg-laying, or oviposition.
My work has shown that DlEPV is highly pathogenic to fruit fly hosts of the wasps, suggesting that the disruption of fly physiology caused by the virus may aid young parasitoid wasps developing within by compromising the host immune system and development.
Furthermore, when wasps are experimentally “cured” of their DlEPV infection, they rarely survive to adulthood. This tells us that DlEPV is, in fact, a mutualistic virus, given the highly beneficial impact it has on parasitoid wasp fitness.
Viral Genome Analysis
Most other beneficial viruses associated with parasitoid wasps are integrated and dispersed throughout wasp genomes. Virus replication in these systems is controlled by the wasp, and the virus is no longer an autonomous entity. Therefore, these viruses are considered endogenous viral elements (EVEs) rather than true viral symbionts.
In the D. longicaudata system, I sequenced the DlEPV genome and surprisingly found that it is not integrated within the wasp genome but rather retains many features of its pathogenic ancestors.
I also found that DlEPV likely originated as a fly pathogen, which would make sense given the fruit fly hosts of its associated parasitoid wasp. Plus, I uncovered wide-scale differences in viral gene expression between wasps and fly hosts that support a novel method through which DlEPV is controlled during its replication within the wasp.
These findings give insight into how a non-integrated (exogenous) virus can persist within a parasitoid wasp lineage. They also support that DlEPV is a true viral symbiont, due to its replicative autonomy apart from the wasp, as well as its massive benefit to wasp survival.
Mutualistic Virus Transmission
As permanent components of wasp genomes, parasitoid EVEs are transmitted to their young strictly through the wasp germline. However, the fact that DlEPV maintains an exogenous genome suggests that it may utilize a unique mode of transmission to infect future generations of D. longicaudata wasps.
I first looked at possible routes of DlEPV transmission within fruit fly hosts, but found virus spread in flies is limited to injection straight into the larval body cavity. It appears then that the ancestral transmission routes of insect poxviruses have been lost for DlEPV in favor of those routes facilitated by parasitoid wasps.
Next, I explored how DlEPV is spread among D. longicaudata wasps. I used a colony of virus-free wasps to show that DlEPV could be reacquired by uninfected wasps externally during development. Once the virus is reacquired, wasps immediately regained their advantage during parasitism.
These results indicate that DlEPV employs post-hatch transmission to infect female wasp offspring, which has not been documented for a mutualistic virus to date.
Prospects for Biocontrol
DlEPV has now been identified as a highly lethal pathogen against major fruit fly pests, such as the Caribbean fruit fly, Anastrepha suspensa. This presents a unique opportunity to study the molecular basis of DlEPV virulence in order to exploit virus-derived tactics in future fruit fly biological control innovations.
Several genetic tools have been developed in this system already, such as my use of RNAi to knockdown viral gene expression in D. longicaudata wasps, as well as CRISPR genome editing, which has been developed for several tropical fruit fly pest species. These tools, when used together, present a powerful approach to identify possible viral effector genes that cause fly death.
In the long-term, this knowledge could be used to develop novel bioinsecticides that leverage viral effector genes for fruit fly pest suppression. Parasitoid viruses therefore represent a previously hidden world of natural biological systems that can ultimately be used to target pest species.