A deadly chemical that targets baby mosquitoes is much more effective when attacking Zika virus than traditional insecticides, according to a new study.
The study from Florida International University looked at the effectiveness of mosquito spraying in areas of Miami impacted by the Zika virus. It analyzed methods of mosquito control, including larvicide and adulticide, that were deployed when the first case of locally transmitted Zika was reported in South Florida in 2016. The research found that larvicide was better for the ecosystem and human health.
Dr. Phil Stoddard is the author of the study and the Mayor of South Miami. He joined Sundial to talk about the results of the report and some of the major issues facing South Miami.
WLRN: Why is larvicide reportedly more effective than insecticide in killing mosquitos?
Stoddard: If you kill the kids they never hatch out and become the adults. Knocking down the adults really is a game of Whac-A-Mole because when you knock them out they always seem to get replaced by more. What the data showed from the different attempts at controlling mosquitos during the Zika outbreaks, was that every time the sprays were successful at killing adults they bounced right back -- the population came right back. The mosquito population mostly consists of newly emerged adults. They're flying around and easy to kill but they're always being replaced from that pool of larvae (baby mosquitos) and pupae that are out there. Going after the kids, the larvae, cuts it off at the base and ends the cycle. The data showed it was effective.
What's the difference between larvicide and insecticide?
Insecticide is anything that kills insects and they come in three classes. There are adulticides, which kill the adults. There are larvacides, which kill larvae (baby mosquitos) and then there are chemicals that prevent the pupae from hatching -- developmental inhibitors. What seemed to be most effective was the larvicide and the least effective turned out to be the adulticides.
What are the risks that we face with insecticides? Do we have the same issue with larvicides?
The classes of insecticides that make up adulticides are the organophosphates, which include Naled and Chlorpyrifos, which have recently been banned in U.S. food products. Those are really effective on insects.
The other classes we like to use are the Pyrethroids. They're synthetic derivatives of the Chrysanthemum flower and are pretty effective. All of these have problems. The organophosphates, like Naled, kill honeybees, butterflies and they shouldn't be applied near marine environments. The Pyrethroid build up particularly in the marine environments, which creates worry about the long-term effects on our shrimp populations and the marine ecosystem.
Did you see anything that came from the 2016 scare? Any damage to the environment, to species or people?
There was a lot of honeybee death and there were a few people who had some pesticide toxicity. Normally healthy people are good at detoxifying these two groups of pesticides. There are a few people who are sensitive and get Chronic Fatigue Syndrome if they are exposed. The other group that shouldn't be exposed is pregnant mothers, which are exactly the same group that we were trying to protect in the Zika situation.
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