A paranoid man is a man who knows a little about what's going on.
-- William S. Burroughs
A new disease is making the rounds, and much like swine flu, bird flu, , AIDS, SARS, and pretty much every other "newly discovered" disease that has gone before it, the Zika virus is bringing with it not only real pathology, but also the imagined kind.
As Zika does pose some actual (though relatively minor) dangers related to infectious disease, and those dangers can be mitigated by proper gardening hygiene, now seems like the perfect opportunity to revisit some thoughts on mosquito control vis-à-vis permaculture.First off, a little primer on this "Zika" business. The Zika Virus is a species in the Flavivirus genus, which includes the West Nile virus, dengue virus, tick-borne encephalitis virus, yellow fever virus, zika virus and several other viruses which may cause encephalitis. This makes it a relative of some of the nastier mosquito-borne tropical diseases, though as of October of 2015, the outbreak of Zika in the Americas had resulted in fewer than 200 cases, and zero deaths. Its potential for fatality is at present unknown, though it has been theoretically linked to a higher probability of encephalopathy and microcephaly (lack or malformation of brain tissue) in pregnancies where an expectant mother had the infection during the first trimester. Research on this question is still sketchy, owing to the newness of the disease, but it makes sense, even if both the causation and quantification are neither clear nor overwhelming.
As with all mosquito borne illnesses, most folk have a relatively sketchy understanding of exactly when and where they danger really lay. For starters, Zika (much as with West Nile) is associated with only one particular species of mosquito, the daytime-active Aedes aegypti mosquito, which (as its name suggests) originated in Africa, but has migrated to every tropical and subtropical environment in the world.
Unlike the vectors for West Nile (Culex pipiens in the Eastern and Northern United States, Culex tarsalis in the Midwest and West, and Culex quinquefasciatus in the South), Aedes aegypti is a year-round pest, though there are some limiting factors. They most commonly bite at dusk and dawn, indoors, in shady areas, or when the weather is cloudy, although the Centers for Disease Control warn "they can bite and spread infection all year long and at any time of day." West Nile mosquitoes, on the other hand, are typically nighttime active, and require heat and humidity in order to breed, meaning that they are most dangerous from late Spring to early Autumn.
CDC recommends the use of repellents with DEET (N, N-, 20% to 30% concentration, but not more), and this advice has been the guiding principle for several decades now. Unfortunately, a 2013 study has suggested that, while mosquitoes do, in fact, hate the smell of DEET, they have learned to adapt. A non-genetic modification to mosquito behavior suggests that they are collectively capable of overcoming their revulsion to chemical aversion in much the same way that beer-goggles make barflies more attractive to each other at last call in pubs around the world. Quite simply, if everyone in your backyard is wearing DEET (or if you are there by yourself), the mosquito thinks "Oh, well. Sure, she stinks, but she's the best blood-on-the-hoof I'm gonna be able to exsanguinate."
Myrtle, of course, never passes up a chance to say "I told you so" (what can we say, chickens are cantankerous, and opinionated). DEET is seldom fatally toxic, but numerous studies have associated it with various rashes, irritations, and inflammations, in addition to insomnia, ill-effects on mood (especially for those who already suffer from mood disorders) and, as with most manufactured chemical additions to one's personal environment, passes across most membrane barriers and combines with numerous other chemical additives in increasingly unpredictable ways.
As with practically everything else, fully studying DEET is virtually impossible. The fact that so few regulatory agencies throughout the world can agree on what concentrations to call "safe" -- coupled with the fact that it is becoming increasingly less effective over time -- suggests that a different method of mosquito control ought to be our response to the increase in mosquito-borne diseases.
There are, as luck would have it, natural means of disrupting the interaction of all mosquitoes (whether one of the Culex species, or one of the Aedes blighters), and some simple prevention measures which make mosquito-to-human transmission of viruses less likely. We have discussed some of these strategies before, but they are well worth revisiting.
|Typical Bti "dunk"|
First and foremost, an understanding of mosquito ecology is essential. Removing or properly treating standing water is near the top of practically every municipal mosquito control checklist; there is some validity to this, as mosquitoes lay their eggs in water, where the larval stage of the insects develop. However, there is significant misunderstanding of which bodies of water are most to blame for the spread of mosquitoes. Ironically, the larger the body of water, the less likely it is to be your villain. The reason is fairly simple -- the natural predators of mosquito larvae are likely to live in ponds, ditches, slow-moving creeks, etc. They are not likely to live in spare tires, buckets left standing open-end-skyward, clogged drainage gutters, or any other containers or non-draining surfaces. For those of us who hate mosquitoes, there are few sounds as joyous as the incessant din of amphibian romance. A frog gone a' courtin' is a human's best friend. Dogs are a distant second. But tadpoles don't live in gutters, so make sure yours are clear. Search your property high and low for puddles and other forms of standing water. This is especially true from May to October regarding West Nile, but now with Zika, we must be more vigilant in Winter, as well (and, to be honest, we at Myrtle's place have historically been lax at the end of "West Nile Season"… well, no longer).
For larger bodies of water (ponds, fountains, etc.), mosquito dunks ought to be used. These are floating donut-shaped formulations used to spread a bacteria known as Bacillus thuringiensis serotype israelensis (Bti). This bacteria has the happy habit of feeding on the larval stages of mosquitoes, fungus gnats, and , but ignoring other organisms. This is especially fortuitous, as other serotypes of Bacillus thuringiensis do, in fact, harm other creatures, most notably bees and butterflies. The use of dunks has two major advantages therefore -- first, it helps control mosquitoes, and second (and almost as importantly), the spread of Bti takes away an ecological niche which would otherwise be filled with harmful species.
For controlled bodies of water (rainwater collection ponds, fountains, or aquaponic tanks), several predatory species can be grown which are great at mosquito (Gambusia affinis), some cyprinids (carps and minnows), killifish, and tilapia all love to chow down on mosquito larvae. None of these predators ought to be introduced to the wild, of course, as they are invasive , but for contained environments, they work wonders.
The next component of ecological mosquito control relates to the habitat of the full grown mosquito. No matter how careful we are about monitoring mosquito breeding habitats, some will grow to maturity. And adult mosquitoes don't live in the water, though few people stop to consider where they do live. So... "Okay, Myrtle, where do adult mosquitoes live?" Glad you asked. They live in tall grass, leaf piles, piles of rotting debris, under stacks of lumber, behind boxes in outdoor sheds... pretty much anywhere dark and moist.
That includes in mulch in your garden, by the way.
|Where adult mosquitoes hang out|
So, unless you are willing to poison anything and everything which comes into contact with any and all of those hidey-holes (and we strongly recommend that you not do so), some other mitigation strategy is necessary for dealing with adult mosquitoes. Happily (particularly vis-à-vis mulch in your garden), there is an extremely simple, low-maintenance method of dealing with the full grown mosquito, and it is hinted at by why the DEET-only strategy has become less effective. Essentially, relying on DEET means there is only one tier of deterrence for the mosquito to overcome. But we know (based on the studies explaining DEET's effectiveness at grossing them out with its particularly mosquito-unfriendly-rankness) that mosquitoes will avoid certain smells, if at all possible.
The only thing left to do is to figure out which smells they naturally avoid, and then layer our outdoor habitation with as many of those smells as possible.
And as luck would have it, you really ought to be growing a lot of these plants, anyway. They are all the "smelly herbs" and the more of them you have, growing in as random an array and in as many different places on your property as possible, the better. Catnip, mint, basil (all varieties), oregano, rosemary, lavender, fennel, oregano (all varieties), thyme, honeysuckle, trumpet vine, cilantro, parsley, anise, bay , borage, fenugreek, chives, onions, leeks, garlic, ginger, horseradish, hyssop, marjoram... anything you have ever picked up at the farmer's market and thought "Oh, my, that's a strong smell" -- get some seeds or seedlings, and go wild. And, as many of these things are either perennials, or reseed as easily as any plants imaginable (the secret to growing them year round is chicken poop plus neglect), the amount of maintenance involved in a mosquito-repellent garden is as minimal as you care to make it.
The big key, of course, is that the smells must be layered, and they must be random. An herb garden laid out in neat rows, plainly labelled and arranged to suit a cook... that may get you in Better Homes and Gardens, but it won't stop the mosquitoes. No, far better to plant willy-nilly, and mix it up. That keeps the mosquitoes from acclimating to the pungency of your ; they take a whiff or two of your garden, and keep right on trucking, and if your neighbors were not savvy enough to follow your haphazard example, well, they can just stay inside and hope all their windows and doors are properly sealed, while you sit on your porch, sipping your lemonade in mosquito-free comfort.
As with our recent discussion of cockroaches, the simple reality is that there is no hope of ever eradicating mosquitoes, and therefore we will continue to hear of new epidemics like the Zika fever outbreak of 2015-16; viruses evolve more rapidly than any other living things, and they are borne by mosquitoes, so news like this is inevitable, and will continue for as long as there are people to report it.
The best we can hope for is to learn and adapt ourselves, so that we may mitigate the harm that comes from our interactions with the rest of the natural world. We only run into real trouble as a species when we forget that Homo sapiens are part of a much larger system than our own immediate surroundings.
Since it is just about time to be putting new plants out for Spring, and since we are entering the final stages of the latest El event, it's a good time to think about implementing these strategies into our yards/gardens/patios/porches, not just to stave off Zika, but to keep ourselves healthy and protected from whatever the next Zika turns out to be.