Zika virus is transmitted by mosquitoes and people.
So, health authorities have been working on the twin challenges of eradicating mosquitoes and educating people.
Transmission of Zika virus from mosquitoes to people (and vice versa) in the continental US has occurred only in one small tropical enclave: a square mile (or now it seems even less) of Miami. Pennsylvanians might worry about catching zika from travelers returning from the Rio Olympics but not from mosquitoes this summer so far north. (1)
However, we should be worrying about the effects of being sprayed with pesticides, of which there is really no safe level for the environment and human exposure.
As someone involved in the current campaign to cut down on both mosquitoes and pesticide spraying in West Chester, I think we can learn a lot from zika, even if it is not currently being transmitted by mosquitoes anywhere near us.
Many insects, like the viruses that attack the human body, reproduce quickly and can develop resistance to whatever we throw against them. As doctors turn from one antibiotic to another to find one that still kills a given virus, so health officials experiment to see what still kills different mosquito species.
The Aedes aegypti mosquito, the chief transmitter of zika, is particularly problematic for traditional mosquito elimination programs and the standard anti-mosquito pesticide permethrin, a pesticide usually applied from ground-based equipment such as trucks. (2)
Aedes aegypti has been acquiring immunity in Thailand (3) to permethrin and even to DDT (which was banned in the US in 1972 after severe impacts such as almost driving our national bird into extinction); and similarly in Mexico (4) and, more recently, in Puerto Rico (5) and now Florida. (6)
As time goes on, scientists have to look farther up the pesticide chain—with further likely risks—to find more effective pesticides. This is not good news.
When permethrin fails, specialists are turning to naled (7), a chemical dispensed from airplanes (now daily, over ten square miles of Miami) in very fine particles.
When pesticides are applied from airplanes, droplets drift farther, potentially affecting more habitats (and hypersensitive people) than from ground-based application. People in Puerto Rico don't want to be sprayed with naled, to put it mildly (8) The Union of Concerned Scientists, not surprisingly, expresses more concerns about naled than does the EPA. (9)
If mosquitoes develop resistance to both permethrin and naled (10), what will be the next pesticide of choice? With what effects?
Let's not find out! Communities need to take all measures now to stay off the pesticide chain and the slope of increasing insect resistance.
As Dr. Thomas Frieden, head of the CDC, said about the zika-affected area in Miami, "Everyone has to be involved and try to find every drop of standing water and get rid of it." (11)
So everyone here, while mosquito-carried zika is still a distant threat, please look around for sights like the one below (photographed in West Chester last month) and educate your neighbors about regularly dumping out all water standing in recycling containers, trash cans, plant saucers, pet bowls, bird baths, tires, and anywhere else. Let's not get to the point of Puerto Rico, where volunteers recently were recently organized to go door-to-door on a "Clean-up Day" helping people to eliminate breeding sites, or Florida, where the government is paying employees to do it. Here, we can still rely on citizen cooperation.
Also, be aware that adult mosquitoes like to hang out in the shelter of brush, weeds, and long grass and in humid areas (you are less exposed on your patio than at a compost heap or stream bank). So you might want to deal with both breeding sites and hang-out sites at the same time.
(1) "Since the 1950s, it has been known to occur within a narrow equatorial belt from Africa to Asia" (Wikipedia).
(2) According to "Spraying Begins in Miami to Combat the Zika Virus" by Lizette Alvarez and Pam Belluck, New York Times, AUG. 4, 2016:
The Aedes aegypti mosquito has several bad things associated with it," Dr. Lyle Petersen of the C.D.C., who is managing the agency's Zika response, said in an interview. "It tends to breed in small pools of water, which are ubiquitous in any urban environment, and tends to be hard to reach. It tends to breed in cryptic environments that are hard to find. And it's just very hard to get rid of."
The traditional methods used in Miami - truck-mounted spraying and backpack spraying with two types of pyrethroid insecticide - have not killed enough mosquitoes, Dr. Petersen said. He said Naled, an insecticide that has been widely used in Florida but not in Miami, might work against city mosquitoes that could have become resistant to pyrethroids, the insecticides that had been used. He said the plan was to spray once a week with Naled to kill adult mosquitoes and once a week with insecticide to kill larvae.
(3) La-aied Prapanthadara et al., “Mechanisms of DDT and Permethrin Resistance in Aedes aegypti from Chiang Mai, Thailand,” Dengue Bulletin vol. 26, 2002 185-189.
(4) Adriana E. Flores et al., "Resistance to Permethrin in Aedes aegypti (L.) in Northern Mexico," Southwestern Entomologist, June 2009:
...Frequent use of insecticide... has led to chemical resistance in many arthropods and this led to operational problems in vector control programs. In 1947, the first case of mosquitoes resistant to insecticide was observed in Florida where the mosquitoes Ae. taeniorhynchus (Wiedmann) and Ae. sollicitans (Walker) showed resistance to DDT (Brown 1986). The problem increased during the following decades....
(5) "Insecticide Resistance Testing in Puerto Rico" at CDC, including mosquito resistance to permethrin.
(6) Lena H. Sun, interview with CDC Director Dr. Thomas Frieden, "CDC director: Sporadic Zika cases possible for months, maybe year, in Florida," Washington Post, 8/3/16 (also, from the video, source of aerial spraying image above):
It's possible the mosquitoes in the affected Miami area have developed resistance to certain insecticides. Over the next few days and weeks, CDC and local officials are testing to see which insecticides will work best. In the meantime, Miami and Florida are considering aerial spraying to kill adult and larval mosquitoes.
(7) The EPA describes naled in this way:
For mosquito control, naled is applied as an ultra-low volume (ULV) spray. ULV sprayers dispense very fine aerosol droplets containing small quantities of active ingredient insecticide that drift through the air and kill mosquitoes on contact. The amount that reaches the ground is small. For mosquito control, the maximum rate for ground and aerial application is very small.
(8) Per Jason Beaubien, "Zika Cases Surge In Puerto Rico As Mosquitoes Flourish," NPR, 8/5/16:
A plan for aerial spraying of an insecticide called Naled caused an uproar here. San Juan's mayor called the plan "environmental terror" and late last month the governor blocked the proposal. Naled is the same chemical that's being sprayed from planes over parts of Miami to combat Aedes aegypti mosquitoes there.
(9) Juan Declet-Barreto, "CDC's Efforts to Combat Zika in Puerto Rico Hampered by a Legacy of Mistrust," Union of Concerned Scientists, 7/28/16:
...the CDC and the PRDOH have recently come under fire from broad sectors of Puerto Rico's civil society after announcing their intent to conduct aerial spraying ("fogging") over the island using naled, an organophosphate pesticide with potential toxicity to humans and debatable effectiveness in controlling Aedes aegypti populations. The EPA has stated that recent naled tests in Puerto Rico were highly effective in controlling mosquito populations. However, the agency deemed naled unsafe for use in or around the home, precisely the habitats that Aedes aegypti prefers, according to Dr. Duane Gubler, who conducted a similar, dengue-focused naled spraying campaign for the CDC in Puerto Rico in 1987: "The [Aedes aegypti] mosquito lives in closets, inside garbage, indoors… [t]hose conditions are less than ideal for mass spraying campaigns”.
Naled is also a "broad spectrum" insecticide, meaning that while it can be effective in killing mosquitoes, it can also adversely affect beneficial insects like bees, pollinators of citrus and coffee plants, important agricultural commodities in Puerto Rico. There's also a lot of concern about naled's potential to adversely affect humans.
(10) The EPA also says about naled: "Mosquito resistance is not an immediate concern, since all mosquitoes from Puerto Rico tested have been found to be susceptible to naled. Despite many acres across Florida being sprayed with naled each year, no resistance to it has yet been detected." The "yet" is the problem!
11) Above-mentioned interview (video, 1:22).