OWENS VALLEY MOSQUITO ABATEMENT PROJECT

Many of you don’t know that mosquitoes have a complex life cycle. OVMAP tries to take advantage of this by targeting the stage of development easiest to contain and thus, treat.

 

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Picture: University of Georgia

From this diagram showing a typical standing water mosquito’s life cycle, you can see several stages. This is a complete metamorphosis, common among the Dipterans (the flies), the Order of insects mosquitoes belong to. With mosquitoes, all of the stages (besides the adult) require water to grow.

 

 

After mating and a blood meal, the female mosquito seeks out a suitable water source which to lay an egg raft, typically a couple hundred eggs.

 

Only female mosquitoes take blood. Now we’d all like to believe this is for some Hollywood vampire, post-coital, demonic blood lust, I mean, why else would something so devilish as a mosquito exist? But a closer look will reveal a more earthly, biological reason.  

 

With few exceptions, the protein from your blood is needed to produce each clutch of eggs she will produce during her lifetime. To seek out that obligatory warm snack, she can detect movement, sense exhalations in the form of carbon dioxide and lactic acid, or sense odors from long distances. Male mosquitoes typically feed on nectar from flowers and some play small roles in pollination.

 

The eggs she’s deposited will hatch, shortly after laying, into larval mosquitoes. The larvae breathe air through a siphon at the very end of their abdomen from the surface. They feed by relying on oral brushes to pull bits of organic matter into their mouths. So, they essentially hang upside down with an abdominal grasp on the surface tension of the water while they breath, then dive toward the bottom to feed and evade predators.

 

As they grow they will go through four molts, each one slightly bigger than the last. The growth rates of larval mosquitoes depend on the species, the amount of food available, and the temperature of the water. In mid summer, when temperatures are at their highest, growth rates from egg to adult can be less than a week leaving a very short window for larval control operations.

 

Pupation takes place after the larva reaches maturity. Inside the pupa massive changes are taking place, as the lava transforms into an adult mosquito. There is no way for the pupa to eat as even its mouthparts are changing into the piercing and sucking hypodermic proboscis we all know so well.

 

The pupa hatches into an adult the cycle begins anew.

 

So which of these stages of life would be the easiest to control? Well, the adults are out in the open air, the eggs are very small, only last a short time before they hatch, and hard to find, and the pupae don’t eat, leaving the larval mosquito as the target of choice.

 

Treating mosquito larva in the Owens Valley starts with finding those sources of water that raise mosquitoes. We live in a dry country and with a dry country comes irrigation. The DWP allotment of irrigation water for the irrigation season is 5 acre-feet per acre of land. The irrigation season starts April 1st and extends to September 31st. One acre-foot of water is an acre of land with a foot of water on it, or 43,560 cubic feet of water, or 325,851 gallons of water, or 2,718,144 pounds of water, or a lot of water, you get the point.

 

As the water spreads out over the land, the bulk of it does what it’s supposed to do and waters the feed for the cattle and nurtures the trees and other plant life in the valley. Some of it however, on its way into the ground, creates vast ponds that stay filled with water for weeks providing the best mosquito habitat on the east side. All the irrigated pastures provide the perfect sources for those female mosquitoes to lay their eggs in. Couple this with the vast stretch of river that run down the middle of this Valley and you have the 1700 square miles within the boundary of the Owens Valley Mosquito Abatement Program.

 

Oser says, “The river’s potential by itself has brought me to my knees in tears several times.”  A steady flow of 400 cubic feet per second is very controllable from a mosquito man’s standpoint, but throughout the year the river fluctuates due to snowmelt and summer storms, as any fisherman or worthy river “tuber” knows. If the flow reaches 600 cubic feet per second, the river spills its banks into thousands of eons-old river channels and oxbows forming stagnant ponds that can last for months.  Last year, the river section east of Big Pine was running at over 1000 cubic feet per second. This is why, despite our best efforts, mosquitoes will always be a part of mid-summer fishing down at the river.

 

With the re-watering of the Lower Owens, we anticipate, at least initially, similar large-scale mosquito hatches with the seasonal flow changes. We ask for a little patience as we seek out mosquito breeding sources and make them a part of our treatment schedule. 

 

To date we know of thousands of sources ranging in size from kiddy-pool size holes that big bulls dig to show their reproductive prowess, to multi-acre tule ponds, lots of them within a stones throw from schools and large neighborhoods. Many of you would be surprised to learn just how many millions of mosquito larvae are growing, every summer, so close to your own neighborhood.

This picture shows a small sample from a multi-acre river oxbow. If all of these larvae, and we’re talking millions, in the oxbow were allowed to hatch into adults and you unknowingly happened upon them, a visit to the local blood drive would be nothing compared to the blood loss from the hundreds of bites you would receive as you ran, arms flailing, back to your car.

 

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Larvaciding

Once a source is found and documented it is checked for mosquito activity twice weekly. If larvae are present then a treatment is made. Treating mosquito larva takes up most of our time here at OVMAP.

 

The material used to treat mosquito larvae by the OVMAP is fascinating as it is totally biological. It is akin to using ladybugs to treat your garden for aphids.

 

It is a bacterium called Bacillus thuringiensis israelensis or Bti for short. It is remarkable in its selectivity only affecting mosquito larva and a few related species. This is a major change from the chemical control of old and a major plus for the environment. This means that any of the other insects in the water, and there are plenty, treated will suffer no ill effects from the treatment.

 

The mode of action, or the way it works, has to do with crystalline inclusions that the bacteria make within their cell wall. These crystals, once ingested by mosquito larvae and broken down, have very potent insecticidal properties that quickly kill the larvae that have made the mistake of dining on them. The key is that the crystals only break down in an alkaline, or a high pH, environment. Very few animals have a digestive system that can be called alkaline, most, like us antacid-popping Homo sapiens digest food with the help of acids. Not so with mosquito larvae. They are part of a super-family of insects with an alkaline gut making them and only them susceptible to the toxins within the Bti.   

 

The down side to treating mosquito larvae is that it is very labor intensive. The Bti only persists in the environment for a few days making repeated treatments necessary. This is why we employ the use of ATVs in our day-to-day treatments.

 

Adulticiding (Spraying)

 

Spraying refers to the practice of adulticiding for mosquito control.  OVMAP does have adulticide in its mosquito control arsenal. I’m sure you have heard the fogger rumble by your house in the wee-hours of the morning. Many people think this aspect of mosquito control is all we do, but in fact, represents only about 5 percent of our time.

 

Adulticide has to be part of the program as a last resort if adult mosquitoes get out of hand, and it does have benefits. It is very quick at what it does and if conditions are right, relief from mosquito infestation is immediate.

 

In the case of the West Nile virus positive horse reported in Independence in August of 2004, we reacted with a massive adulticiding campaign to target mosquitoes infected with the virus in the Independence area. Subsequent post-fog mosquito traps set in the area fogged revealed a very good kill of the target mosquito species.

 

The benefits of adulticiding are not without a cost:

  • The control offered by the chemicals used if fogging is temporary, providing no residual control, and must be repeated if more adult mosquitoes move into an area.
  • The chemicals involved are very expensive.
  • Mosquitoes may develop a resistance to the chemicals with repeated use.
  • The chemicals are not selective. They will kill anything with an exoskeleton that will succumb to the dosage rate applied. So many beneficial insects could be lost in the name of a Labor Day BBQ. Studies have shown that whether or not an insect is susceptible to the dosage rate applied is a function of the size of the insect. Insects and other arthropods the same size or smaller than your typical adult mosquito are more likely to succumb to the effects of the pesticide than something the size of a dragonfly.

And let’s face it, adulticides are chemicals and we are putting chemicals into the environment and that is good for nobody except... err… well it’s good for nobody. This is the big reason OVMAP tries to only use this portion of its control program as a last resort, when all else fails.

Other regions have recognized our program as being well managed and progressive in what is best described as a challenging environment, which is basically the greater part of a river basin. 

MISSION STATEMENT

The mission of the Owens Valley Mosquito Abatement Program (OVMAP) is, and always has been, to protect public health and welfare through the detection and control of mosquitoes.  OVMAP is conducted from the Mono County border in the north to 3 miles south of Olancha, and bordered on the east and west by the White Mountain and Sierra ridges.

 

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pdf.gif Mosquito Complaint Form

 2006 OVMAP Annual Report

 2007 OVMAP Annual Report