news from the waterfront by Tim Matson
With bug season in the wings, this month Tim reviews a wide spectrum of mosquito prevention strategies. As if pond owners didn't have enough worries with mosquito borne West Nile virus and Eastern Equine Encephalitis, now there's Zica, another mosquito vectored virus. Studies are underway to confirm a variety of Zica effects, including several types of birth defects, as well as fevers, eye problems, and more. Because Zica had been confined to southern regions like South and Central America, those in more temperate zones seemed outside the target area. But climate change is pushing southern weather north (witness the non-winter winter ending in Vermont), and new illnesses with it. Consider how to discourage mosquitoes in Ponds Debugged! reprinted from summer 2013.
In my neck of the woods winters are long, so when a whining mosquito announces the arrival of spring it’s usually a decent tradeoff for green grass and warm sun. No more. Now an itchy mosquito bite may mean more than skin irritation. Over the past decade, mosquito borne West Nile Virus has been sickening and killing people (and critters) nationwide at record rates. Same for Eastern Equine Encephalitis. Disease experts connect the virus rise to insect friendly climate warming. If you own a pond or plan building one, pond safety has a new dimension.
Mosquitoes need water to reproduce, so ponds
have the potential to become breeding areas.
Here are some strategies for discouraging these insects. These controls use non-toxic methods and avoid poisonous insecticides.
Create Deep Water
In general, deep water is not a good medium for
mosquito breeding. The female mosquitoes that lay
eggs and their larvae prefer still warm water,
in tires, buckets, and anything that will hold some stagnant water. In ponds, this kind of water is often found around shallow edges. Depending on the mosquito species, the female may deposit eggs on water directly or where the larvae attach to aquatic plants, roots, etc. So if you deepen a shallow shoreline area, and remove plants like cattails from edges, you’ve reduced the mosquito breeding territory. And when building a pond, excavate edges with a slope of two or three to one.
Bring on the Predators
Mosquito predators can be another control for the insects. These can be stocked, like fish or crustaceans, or attracted to the pond, like birds and predator insects. Some predators will inhabit a pond naturally, like frogs. Tadpoles and frogs are effective larvae and mosquito eaters.
Let’s start with crayfish. I’ve long maintained a population of crayfish in my pond, mostly for algae control because of their effectiveness at eating up nutrients that feed algae, as well as small submergent vegetation. They also eat mosquito larvae and pupa. A nice two-for-one effect, with no toxic chemicals involved. A fish farmer nearby is beginning to offer a combination of 3” brook trout and crayfish for mosquito control. Why brookies? They’re native to rivers and brooks, and effective at nosing into shallow pond edges for tasty mosquito larvae. Combined with the crayfish, they make a good defence against mosquitoes.
Many other types of fish are reputed to be hungry
for mosquito larvae. These include various types of
minnows, especially the surface eating variety.
The gambusi, also known as mosquito fish, is perhaps best of all, although it’s territory may be limited to temperate climates. Tilapia (also climate constrained) and carp are also credited for mosquito control.
Amphibious forces can be rallied for the fight against mosquitoes. In its underwater stage dragonfly larva eat mosquito larva. And once airborne, dragonflies gobble up mosquitoes in the air. Dragonflies commonly naturalize at ponds, but larvae are available from specialized suppliers for stocking in the spring. Keep in mind that fish stocked to control mosquito larvae may also eat dragonfly larvae.
There are many bird species credited with mosquito eating skills, including purple martins, swallows, the common nighthawk, chickadees, nuthatches, mocking birds, robins, and woodpeckers. Putting up bird houses and planting flowers to attact these birds should help encourage them to patrol your pond. Hummingbirds are also known for mosquito control, and they like sweet water feeders, as well as colorful flowers.
Bats are another great airborne mosquito killer,
doing most of their work in the summer dusk and
evenings. Putting up bat houses is one way to
encourage them to settle near your pond, and
they can also create their own nests in the cracks and crannies of trees, houses, barns, and outbuildings. Unfortunately, recent declines in the bat population due to disease put a big dent in bat numbers, and unless they bounce back on their own, or with our help, these mosquito eaters may have lost their punch. In fact, the rise in mosquito born diseases may be connected to bat decline.
Rounding off the list of critters you can add to the pond is neither fish nor fowl. Baccillus thuringis (bti) is a bacteria that feeds on mosquito larvae. BT is a natural pest control familiar to many gardeners who use it to stop plant eating bugs. It can be purchased in floating “dunks” for use in pond mosquito control.
Let’s return to the water for ways to use liquid dynamics to control mosquitoes. This strategy boils down to two words: make waves.
Larvae thrive in the stagnant shallow edges
around a pond, where they like to hang onto
vegetation or float quietly and make their undisturbed transition to pupa and then flying insects. What they don’t like (besides hungry predators) is turbulent water to knock them off their plant perches or disturb their delicate oxygen intake positions. Making waves turns out to be a good technique for upsetting their incubation.
Waves generated by splash aerators are often strong enough to inhibit hatching. The size of the pond, distance from aerator to shore, and wave size will factor into the kill rate. (Diffusion bubble aerators will probably not make a big enough wave to be effective.)
Supply pipes that splash water into the pond may
make waves big enough to affect mosquitoes. Waterfalls can also generate waves that may disturb mosquito larvae. Pond owners with existing wave generators will want to observe their effects to evaluate how useful they are. Starting from scratch and adding splash aerators, fountains, waterfalls, or wave making feeds would require experimentation. What’s your pond size? Is there a splash aerator or fountain that could help with aeration as well as wave generation? Perhaps pumping in extra water or recycling pond water would help?
Climate change, new diseases, and loss of bats add up to unhealthy mosquito conditions. The good news is that pond owners can fight back using natural non-toxic methods.
March 1, 2016