Guest Scientist Blog: Effectiveness of Eco-Friendly Botanicals in Repelling Mosquitoes from Container Oviposition Sites

SEES Mosquito Mapper intern Parker L. in his lab, identifying a specimen recovered from one of his mosquito research traps. Photo credit: Author.

I am fascinated at how effectively Aedes albopictus has expanded beyond its historical geographical origins in Asia, sticking its proboscis into Texas along with every continent across the globe except Antarctica.  This invasive mosquito, which serves as a vector for dengue and chikungunya, has been enormously successful in utilizing alternative breeding containers to supplement its natural oviposition sites.  In fact, it is interesting to note that Ae. albopictus is thought to have migrated to the United States transported within a shipment of tires traveling from Asia to Houston in the 1980s. Today, alongside a variety of Culex species, Ae. albopictus is a common container breeding vector of significant health importance, both within my region and internationally.   At the same time, concerns exist that the world’s deadliest animal—the mosquito—is developing resistance to synthetic chemical insecticides, and whether such insecticides have negative effects on humans, animals and the environment.     

Accordingly, when it came time to design my field experiment, I was interested in testing the effectiveness of eco-friendly botanicals as an oviposition deterrent against container breeders in Texas, and with an eye towards how ordinary residents might use them to help reduce mosquito populations in their neighborhoods or backyards.  Recognizing that container breeding mosquitoes seem to truly love old tires, I set out to attract them to lay eggs by filling a series of old tires with lake water, decaying leaves and grass, spacing them as far as possible from one another in shaded areas.  I then attempted to repel them by closely surrounding the tires with a variety of plants sold or known as mosquito repellent plants, including geranium, lemon grass, lavender, lemon balm and rosemary.

Over the course of a month, all tires surrounded by mosquito repellent plants developed larvae, except for those placed near rosemary-- some of them serving as oviposition sites multiple times after being dumped and reset.  The most prevalent larvae seen throughout this experiment belong to the genus Culex, likely Cx. Quinquefasciatus. This taxon transmits viruses including, but not limited to, West Nile, St. Louis encephalitis and Western equine encephalitis. The speed at which the tires refilled with larvae was startling and underscores the paramount importance of eliminating standing water. In fact, in the ordinary manner and concentrations that a homeowner might use these plants, I questioned whether in the presence of standing water most of these botanicals actually further attracted mosquitoes by providing greater shelter and shade.  Some tires interestingly enough even developed two species of larvae simultaneously, yet with fewer larvae than one would expect.  Although I suspected foul play and that a predator was  consuming my larvae,  Dr. Low kindly assisted in targeting the surprising likely offender—another mosquito larva and cannibal tire-mate—Toxorhynchites.  Arguably, and a bit ironically, this unexpected and huge companion larva provided well more effective mosquito population deterrence than most of my botanicals. 

It has been an incredible experience participating in the NASA Mosquito Mapper Project Internship this summer and having the chance to work with NASA scientists and other high school interns that similarly love science. Throughout the course of our research projects, I have learned so much about mosquito vectors for disease in my area and around globe, how to identify the vector species as larva on a microscope, and a great deal about ecology, all while developing and practicing scientific research skills.  Most importantly, with mosquito-borne diseases causing millions of illnesses and deaths annually, it has been a privilege to be part of a team helping to collect data used to support models that may predict disease outbreaks. 

Parker L.  is a high school student from Texas who is working on a research project this summer using the GLOBE Observer Mosquito Habitat Mapper. His virtual internship is part of a collaboration between GLOBE Mission Mosquito and the NASA  Texas Space Grant Consortium (TSGC) to extend the TSGC Summer Enhancement in Earth Science (SEES) internship for U.S. high school (http://www.tsgc.utexas.edu/sees-internship/). He shares his experience so far this summer in this guest blog post.