Gonad chomping parasites and other things we’re using to keep Zika away

Zika has people turning to all kinds of things to prevent getting the virus, and we’re still missing a lot of information on some of them. So we spoke to Roberto Pereira, research scientist at the Entomology and Nematology Department at the University of Florida and to mosquito expert Tanjim Hossain, a National Science Foundation Graduate Research Fellow at the University of Miami to figure out what works and why — and what’s in that stuff we’re slathering all over ourselves.


How they work: They mask the scent that mosquitoes are attracted to

It’s oil distilled from two grass varieties, with the chemicals citronellol, citronellal, and geraniol. It’s a natural repellent. It keeps the mosquitoes at bay, mildly and for a short amount of time. A study in the New England Journal of Medicine said repellents containing up to 10 percent citronella oil could cut down on mosquito bites for an average of 20 minutes before it wears off.

It’s a chemical that was developed by the U.S. Army in 1946 for soldiers in insect-infested areas. Most repellants have up to 30 percent of DEET in it and that’s pretty effective. It keeps insects away for up to five hours.

Higher percentages of DEET concentration don’t = more effective. Higher concentrations just mean the product will last longer, and at more than 50 percent concentration there’s no added protection. At super high, unsafe concentrations it has caused skin rashes and blisters. Scientists have conducted tests to figure out the safe amounts and  if you follow the label you should be just fine.

“DEET is one of the most effective repellants. A lot of the products you buy will have DEET in it,” according to Pereira.

There haven’t been any scientific studies confirming adverse effects of it at safe levels, but children under two years old should not use the product.

It’s another repellant similar to DEET. It resembles the natural compound piperine, found in the plants that make black pepper. There are roughly two dozen products with picaridin in them in the U.S.


How they work: They enter the mosquito’s nervous system, killing the adult mosquitoes and their larvae.

It’s an insecticide, made up of a mixture of six chemicals that are toxic. It excites the nervous system of the insects that eat it. They are generally low in toxicity for people, but can cause some tingling or numbness on your skin. Some people also report difficulty breathing.

“Over the year there were several [chemicals] that were used in the past and as we get better chemicals the harsher ones are abandoned. The ones we have on the market are all safe and good to use,” Pereira said. “For normal spraying there’s no harmful effects. These are calculated so there’s a large margin of safety for what could cause harm to humans in general.”


How they work: Enter the mosquito’s nervous system, kill the adult mosquitoes and their larvae

The full name is bacillus thuringiensis israelenis. It’s a larvicide that releases toxins only once it gets into the mosquito larva’s midgut and basically kills the mosquito before it can mature into an adult.

It’s an insecticide that is used to kill adult mosquitoes. Other insecticides fall into the category of pyrethrins, but this falls into the category of organophsphates. It’s being used because many mosquitoes might have developed resistance to the pyrethrins, so it’s more effective to rotate the two classes of chemicals, according to Pereira.

It’s a bit contentious because it’s been banned in the European Union in 2012 because it was deemed an “unacceptable risk” for human and environmental health. Protests erupted in Puerto Rico when boxes of naled arrived on the island.

Why is it banned in the EU and discontinued in Puerto Rico but used in Miami then?

“The EU and the US both have access to the same data, scientifically speaking. From a policy maker’s perspective it’s a risk/benefit scenario. The EU, on a basic level, has different climate and doesn’t have the same type of mosquitoes so … from a climate perspective we have a lot more risk,” Hossein said. The increased risk justifies the use of this harsher chemical, he clarified.

Puerto Rico, on the other hand is on the other side of the spectrum and they have have a lot of risk. Still naled isn’t being used.

That’s because  “Puerto Rico has a history of being screwed over by the colonialist policies,” Hossein said.  The public distrust in chemical sprays has been built in so public outcry was particularly strong which prevented naled from being sprayed, he said.

What’s the science? Well, the EPA, says it’s safe in the right doses, but overexposure can cause “nausea, dizziness, confusion, and at very high exposures (e.g., accidents or major spills), respiratory paralysis and death.”

Pereira and Hossain say the quantities being sprayed are so small that they do not present any risks to human health.

According to the EPA:

“Naled is currently being applied by aerial spraying to about 16 million acres within the mainland United States as part of routine mosquito control, but it can also be used following natural disasters such as hurricanes and floods:

  • In 2004, it was used extensively to treat eight million acres across Florida as part of the emergency responses to hurricanes.

  • In 2005 after Hurricane Katrina, five million acres of Louisiana, Mississippi, and Texas were treated with naled to kill mosquitoes.”


How they work: Insect trap filled with larvicide

It’s a bucket full of water and larvicide that attracts female mosquitoes and tricks them into laying their eggs in the bucket. Meanwhile, the female mosquito is exposed to a larvicide fungus, so when she flies to another container to lay another batch of eggs, she takes the fungus with her and it prevents larvae from developing in those containers too.

“Basically, the water becomes a killing environment,” Pereira said. The EPA has recently granted temporary approval for professional use of these traps, fast tracking them so that they can be used to help combat Zika.


How they work: The male mosquitoes are modified so they have deadly DNA

Basically, scientists at the biotech firm Oxitec have created male mosquitoes that produce offspring that can’t survive until adulthood. It seems promising, but lots of people are afraid of what might happen if the scientific experiment goes horribly wrong.


How it works: A bacteria takes over the reproductive organs of female mosquitoes

There’s this bacteria called the Wolbachia that basically finds its way into the a mosquito’s gonads and into a female mosquito’s eggs. Scientists found this one crazy strain that makes A. aegypti mosquitoes (the kind that carry Zika and dengue) less effective at carrying Zika. It’s still in trial mode but could be a promising solution one day.
So is all this stuff really worth it? Both Hossein and Pereira think so.

“With pest control we always talk about IPM — integrated pest management — using several tools and layering things so you have protection at different levels. … each one of these have different characteristics and will be used differently,” Pereira said.

The one product we can all use is repellent, he stressed, because that travels with you where pesticides can’t reach and you can control it at an individual level.

Modern techniques like the Wolbachia and the Genetically Modified Mosquitoes are particularly promising because they wouldn’t have any affect on humans at all, Hossein added.

“But in terms of urgency and the need to immediately contain an outbreak, you need applications of pesticides that are known to work and can be applied in a very short time, and that’s where the naled and pyrethrin come in,” Pereira said.

Still he admits that while he’s “a great advocate of having strong safeguards at the same time, [he’s] a strong advocate of using pesticides judiciously because they save lives. There is a balance to be made between trying to save lives and keep the environment clean and healthy for all of us.”