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Rhodamine B: A New Tool for Monitoring Mosquito Mating
Tuesday, November 21, 2017
We are very excited to announce the Debug Project’s first
publication
, which explores tracking mosquito movement and mating in the wild, a collaborative effort between Verily’s Debug team, The Australian
Commonwealth Scientific and Industrial Research Organization
(CSIRO) and
James Cook University
(JCU) in Australia. The study demonstrated that rhodamine B can be utilized to successfully perform mark-release-recapture (MRR) experiments and observe mating in the field.
Rhodamine B is a red dye that fluoresces when exposed to certain wavelengths of light. When fed to mosquitoes, it binds to internal proteins and stains them bright red. Rhodamine B staining is observable in adult mosquitoes by eye or by a microscope when looking at small tissues, which can be useful when studying mosquitoes in the wild. Mosquitoes can be tracked in the wild using an approach known as mark-release-recapture (MRR) where insects are marked (in our research, with rhodamine B), released into the wild, and then recaptured for marking examination. MRRs provide information on how far mosquitoes move across the landscape, as well as their lifespan, and can help us estimate the wild population size by comparing the ratio of marked recaptured individuals to unmarked insects.
A male Aedes aegypti mosquito fed on a mixture of rhodamine B and honey is stained visibly red (A) compared to males fed on honey alone
(B).
Traditional methods for MRR labeling rely on dusting mosquitoes with fluorescent powders, however, these powders can be difficult to detect and can impair a mosquito's ability to fly. Rhodamine B, on the other hand, can be easily visualized and evidence suggests it does not impact a mosquito’s activity or health.
Rhodamine B labeled males will seek out wild females. During mating males transfer their labelled semen to females, which can be detected by its red fluorescent properties.
Rhodamine B has another useful property: it can stain the male mosquito’s semen, which females store in dedicated capsules called spermathecae. After mating with a rhodamine B fed male, stained semen can be observed in the female’s spermatheca using a microscope. So not only can rhodamine B be used to track males in the wild, it can also be used to measure how successfully they mate with wild females.
Rhodamine B labeled sperm within the female spermathcal capsules after mating.
In our paper, we demonstrate that rhodamine B is a very effective label when mixed into the honey normally fed to male mosquitoes, with the stain visible up to three days after males are released. We performed several small scale MRR experiments in Cairns, Australia and were able to successfully detect mating between our lab reared males and wild females through rhodamine B fluorescence.
For future sterile male releases rhodamine B labeling will be a useful tool allowing us to easily and efficiently assess the dispersal, fitness and mating ability of the males we rear in our Debug factory. We are excited to continue this research and further demonstrate rhodamine B’s utility.
Sara Mitchell, PhD, Senior Scientist, Verily
Wrapping up Debug Fresno 2017
Monday, November 6, 2017
As we begin to wind down
Debug Fresno
operations for 2017, our team has been reflecting on the work of many individuals and groups that brought this study from concept to now near completion. From the development of unique technologies that scale the sterile insect technique, to testing our operations in a real-world environment and quickly adjusting to challenges, our team has achieved strong results from this season’s field study that we are proud to share today.
One of our primary goals at the outset of this study was to see a steep decline in the presence of female
Aedes aegypti
mosquitoes in the area where sterile male mosquitoes were released relative to similar control neighborhoods in Fresno County. Through the analysis of our trap and monitoring data, we found during the peak of the mosquito season there was an average 68% reduction in biting, female
Aedes aegypti
mosquitoes in our release area relative to other similar sites. These are promising results for our first field study, and we are looking forward to expanding to additional sites over more than one season to see what can be achieved.
For the Debug team at Verily, we also wanted to pressure test the first iteration of our technologies in a real-world environment and gather insights that could help us refine our approach. We gained valuable experience in all areas of the project. From larval production, to sorting male and female mosquitoes, to releasing sterile male mosquitoes, to trapping and monitoring, we continually improved our efficiency throughout the season. This experience is already being applied to future studies including Debug Innisfail, which will begin later this month in Australia.
As the mosquito season in Fresno County draws to a close, we want to thank the many people involved in this study, including our collaborators at
Consolidated Mosquito Abatement District
and
MosquitoMate
as well as the residents of Fresno County that have engaged with us in the Debug Fresno study. As our technology and research program continues to grow and improve, we hope to continue to partner with communities to learn how to reduce the threat of mosquito-borne diseases around the globe.
This post is also available on Verily's
blog
.
Jacob Crawford, Scientist and Yi Han, Product Manager
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