Colorado is gloriously sunny, high and dry. That ought to mean living in mosquito-free bliss. But there seem to be more and more reports of mosquito outbreaks, and folks are increasingly concerned about them. Why?
Twilight vampires aside, perhaps it’s because bloodsuckers give us the heebie-jeebies. More likely it’s because our mosquitos increasingly carry West Nile, St. Louis encephalitis and Western equine encephalomyelitis viruses.
Luckily, our mosquitoes are predictable. Like the Creature from the Black Lagoon, their life cycle is tied to stagnant water. Our most common local mosquito can only lay its eggs atop standing water and its brethren only lay eggs on wet soil that later floods. Adult males live about a week and exclusively feed on flower nectar and pollen. Females often live up to six weeks — but suck blood as well. Proteins in blood are needed for most of the eggs that they lay.
Like the amber-encased mosquito from Jurassic Park, today’s mosquitoes get most of their blood from living dinosaurs — aka birds. As they suck on finches, sparrows and quail, they acquire diseases that they transmit to humans, horses, pets and other animals.
Among the dozens of species of mosquitoes inhabiting Colorado, two types stand out. The first includes members of the genus Aedes. These are the fast-breeding ones that carry heartworm larvae that infect your pets. They also bite the heck out of you shortly after your neighborhood is deluged, irrigated, or experiences a spring snowmelt. Aedes eggs need as little as a half-inch of standing water and five days to mature into biting adults. The second group includes members of the genus Culex, which whine in your ear and feed at night. These are the virus-carrying mosquitoes — and typically a tenth of a percent to 10 percent of them are infected. Culex reproduce more slowly, thriving in larger bodies of permanent or semi-permanent standing water, such as ponds, lakes, marshes and drainage impoundments.
Both of these mosquito types owe its abundance to the pond water around us. Some of this water comes from rainwater that accumulates in natural depressions, but much of it comes from our infrastructure and development.
For example, graded land, construction sites and well sites are littered with puddles. Agricultural areas have abundant lingering water in furrowed fields, irrigation ditches and perforated canals. And let’s not forget golf courses, where manmade “water hazards” provide a veritable mosquito bonanza.
To put these in perspective — one flowerpot saucer of stagnant water can produce thousands of mosquitoes per summer. Thus all these sites combine to have profound effects.
Even our neighborhoods contribute to the problem. Manicured developments provide the perfect haven for mosquitoes during the day by providing cool, moist, shady plants for mosquitoes to hang out around and breed. At night, they provide refuges in humid, well-watered lawns.
So what should we do? First, eliminate standing water to prevent mosquitoes from reproducing. Second, consider screening your front door, wearing long sleeved loose-fitting clothing and pants, and minimizing time outdoors at dawn and dusk when mosquitoes are gorging. Third, consider your repellent options. Moderate concentrations of DEET, when used on skin and according to instructions, are safe for the vast majority of people — including kids and most other mammals. But minimize DEET usage in babies, toddlers and pregnant women — this chemical’s effect on endocrine and neurobehavioral systems is poorly constrained. Other chemical repellents like IR3535 or Picaridin are less well tested, but are widely used in Europe and appear to be safe for people. Citronella and similar botanical repellents work, but are less effective. Their side effects in humans are also poorly known and many contain concentrated allergens. Achoo!
As a society, we can best solve our mosquito woes by using integrated pest management programs. These programs are employed by many cities and reduce both nuisance and hazardous mosquito populations. They involve monitoring where and how mosquito populations change so problems are addressed before they get out of hand. Usually this involves eliminating, draining, or introducing bug-eating fish to sites where skeeters reproduce, and bombarding larval populations with mosquito-toxic substances derived from soil bacteria. Where necessary, pyrethroid insecticides can be sprayed at night to kill adult populations. The latter can sometimes damage desirable insect communities, though.
Despite this stinging news, our state’s overall mosquito situation is much improved. In historical times malaria and equine encephalitis were rampant in Colorado. Today’s mosquitoes are mostly a nuisance and don’t typically cause public health emergencies. Yet they can significantly impact our quality of life and our economy. In Colorado, their abundance is mostly catalyzed by man-made activities and structures. Mother Nature just provides some of the water and the entomological potential.
Like immunization, dealing with mosquitoes benefits most from systemic prevention. This weekend, I’ll be checking those flowerpot saucers behind our grill.
James Hagadorn, Ph.D., is a scientist at the Denver Museum of Nature & Science. Suggestions & comments welcome at firstname.lastname@example.org.