Mosquito transmitted pathogens have an enormous impact of human health. A substantial amount of funding and resources are being spent to control the transmission of diseases such as malaria and dengue fever. In many ways this investment is paying off. Innovative and exciting new strategies and technologies have been developed to help combat these plagues.
The next challenge we face is implementing these new tools in a way that is effective and sustainable and to start to make a real impact on disease transmission. It is time to move from the whiteboard in the lab to actually using these new tools in the field. One of the key challenges to implementation of many of these new strategies is that we don't actually know very much about what mosquitoes actually do in the real world.
Our research aims to improve understanding of mosquito behaviour and how behaviour mediates interactions with other organisms, the parasites that they transmit, and the dynamic world that they live in.
Current areas of research fall under two broad categories:
1) Sexual selection, courtship, and mechanisms of female choice in mating swarms
2) The role of vector behaviour in vector borne disease transmission dynamics
Most medically important mosquitoes mate in aerial swarms. Mating occurs in flight and in a matter of seconds. We know shockingly little about what happens inside of these swarms.
Several innovative disease control technologies incorporate the release of transgenic mosquito lines to control disease. Initially, the success and efficiency of these strategies will depend on laboratory reared males competing with wild males for female mates.
We are exploring the mechanisms of female choice and male traits associated with male mating success in the dengue vector Ae. aegypti to help improve the quality of release lines. These experiments include investigations into the best proxies for male fitness in the laboratory and also the effect of different rearing practices on male mating success.
Do male mosquitoes signal information about their quality to females?
When male and female meet in flight they alter their flight tone (that annoying buzz they beat their wings). They change the frequency of their flight tone to match at overtones.
Spectrogram on the right is of a male mosquito in flight. He is joined by a female and they then match at harmonic overtones of their flight tone (males 2nd and females 3rd harmonic). Taken from Cator, Arthur et al. (2009)
Previous work has shown that these signals are associated with mating behavior (Cator et al. 2011), signal characteristics are adjusted depending on the perceived quality of a potential mate (Cator et al. 2010), and signals may contain information about indirect benefits to females (Cator et al. 2011). Many unanswered questions remain about what exactly the information these signals contain. Better understanding these putative courtship signals may help us answer some long standing questions about what happens in mosquito mating swarms. This work centers around a BBSRC funded project with Dr. Alongkot Ponlawat (AFRIMS-Bangkok) and Dr. Laura Harrington (Cornell University).
What traits are associated with male mating success?
In order to give laboratory released males the best possible chance to compete with wild males we need to understand what traits are associated with male mating success. It will also be important to understand to what degree female preferences effect this mating success. We are interested in identifying these traits both in the laboratory and in the field. I'm excited to work with Dr. Courtney Murdock at the University of Georgia and Laura Harrington (Cornell University) on these questions.
Clearly as a behavioural ecologist my answer to this question is a resounding "YES!". However many models of disease transmission ignore components of vector behaviour or do not allow them to vary over time, within a population, or across environments. How important is vector behaviour and variation in behaviour to transmission dynamics?
For example, mosquitoes infected with malaria behave differently and the changes in behaviour vary through time. The output above is from a model created with Dr. Penny Lynch. It is showing predicted effects of altered mosquito feeding patterns on the relative number of infectious bites we expect a population to deliver. In some cases we get fold changes in these transmission predictions and yet current models do not consider this change in feeding pattern especially through time.
I am happy to be working with Leah Johnson (USF), fellow Silwoodian Samraat Pawar, Erin Mordecai (Stanford), and Pete Hudson over the next 5 years to explore the role of vector behaviour in transmission ecology. For more information about VectorBITE objective and events see the new website!
Only a small proportion of mosquitoes are infected with malaria. There is mounting evidence that these females behave differently. These changes in behaviour have been interpreted as parasitic manipulation of mosquitoes by malaria parasites. We are interested in this important subgroup of mosquitoes and understanding how and why they behave differently.
For some background see this Opinion from Trends in Parasitology.
Why do mosquitoes infected with malaria behave differently?
Mosquitoes infected with malaria parasites have been shown to be more or less likely to feed on blood depending on the stage of development of the malaria parasites infecting them. Traditionally, these changes have been interpreted as parasitic manipulation of mosquitoes by malaria parasites. In a recent paper in Proceedings of the Royal Society B, we demonstrate that important aspects of these stage-specific changes in behaviour and sensory physiology can be triggered by a general immune challenge. In collaboration with researchers at Penn State and University of Georgia ,we are continuing to investigate what drives these behaviors and how they may impact mosquito fitness and life history strategies (Image: Transmissible stages of malaria parasites being released from an infected mosquito midgut. Photo taken from the Thomas Lab)
Do these changes in behaviour effect interactions with control tools?
Many of our best control tools for malaria (bed nets and indoor residual spraying) rely on mosquito behaviours. These technologies are currently designed and tested assuming that all mosquito behaviour similarly. How do changes in behavior associated with malaria infection alter how the subgroup of mosquito actually responsible for transmission interact with these tools?
How important are these changes in mosquito behaviour to transmission?
See this work with Penny Lynch in which we investigate this problem.