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Adulticide Treatments

The adult stage the portion of the life cycle most people associate with mosquitoes.The adult stage is the only stage in their life cycle in which they are not fully aquatic, and the only stage in which they take a blood meal. After emerging from the pupal casing, the newly hatched adult will rest on top of the water to dry its wings and body. Once dried, the mosquito is capable of flight.While it varies based on temperature and mosquito species, it can take only seven to ten days for a mosquito to go from egg to adult. With the basic biology of mosquitoes addressed, we can get into the details of how the District program works.

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Here at GCMCD No. 2, the vast majority of our applications target mosquito larvae.The products used to kill mosquito larvae are extremely low in toxicity and do not affect other aquatic organisms. While this part of Grant County is a desert, there is an abundance of mosquito habitat.This is due to the formation of Banks Lake in the Grand Coulee along with natural ponds notably above the Coulee throughout the district. To determine if an area is breeding mosquitoes field technicians sample the habitat using a dipper. A dipper is a small white cup attached to a long wooden handle. The dipper is used to skim the water surface and the technician analyzes the sample taken for the presence of mosquito larvae and/or pupae.

The District also has an adult mosquito surveillance program consisting of trapping mosquitoes and identifying them to help in the formulation of effective control measures. To capture mosquitoes, we use traps baited with carbon dioxide. These traps consist of a bucket containing dry ice, battery operated fan and light, and an external catch net. The carbon dioxide released from the dry ice will attract the mosquitoes. From there they see the light above the fan and fly toward it. As the mosquitoes reach the light, the fan will pull them down into the catch net where they cannot escape. Upon collection, the catch net is separated from the fan, closed, and placed into a container with wet paper towels. These paper towels allow the mosquitoes to drink water and regain moisture which is essential to keeping them alive.

Once the mosquitoes are transported back to the lab, the catch nets containing the mosquitoes are set into a freezer just before beginning the identification procedure.The cold will put the mosquitoes to sleep so that they are easily identifiable. The mosquitoes are then sorted into piles by genus and species.

Larvicide Treatments

There is an abundance of mosquito progeny habitat along Banks Lake and several other manmade or natural water bodies in the district. Additionally, there are water collection sites in urban areas. For areas along Banks Lake the District utilizes a fixed wing aerial application aircraft through an interagency agreement with Grant County Mosquito Control District #1 in Moses Lake. The aircraft can directly target and apply control agents to approximately 300 acres in an hour making it extremely cost effective.

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The target application height is approximately 20-40 feet above the ground and a flight speed of 130 mph. The aircraft is equipped with GPS guidance and application avionics used to precisely apply active agents to within tenths of a pound per acre. Currently it applies dry larvicide granules. The granules are applied directly to mosquito larvae habitat which mostly consists of stagnating water sources. The majority of these active ingredients specifically target mosquito larvae, are organic, and extremely safe. The granules vary in density but are about the size of lawn fertilizer.

While the District tries to avoid flying during holidays and weekends, we do not have a set schedule for application due to changes in weather, water levels, and the countless other variables.

The District also locates and treats much smaller breeding sites when they cannot be drained or through elimination of water holding waste containers. Most of these activities can be achieved through cooperative agreements with property owners, other agencies, political subdivisions and public education.

Field Surveillance

Mosquito control starts in the swamps, marshes, seepage ponds, and any other area that holds shallow stagnant water. To understand why water is critical to mosquitoes, one must understand the mosquito life cycle. Mosquitoes have four distinct stages in their life cycle: egg, larva, pupa, and adult. Depending on the species of mosquito, eggs are laid either singly or attached to each other in groups of 50-200 eggs. When the eggs are joined, they are called an egg raft. Most mosquitoes lay their eggs directly on the water surface where they hatch into larvae a couple of days later. There are also some mosquitoes which lay their eggs on the ground next to the water.

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When the water rises from increased irrigation, snow melt, etc., the eggs hatch and the larvae emerge. Regardless of the mosquito species, all larvae require water to survive.

Once the larvae emerge from the egg they begin filter feeding. At this point in their life cycle they feed only on microorganisms and small organic material in the water. The larvae breathe through a siphon tube that penetrates the water surface. During their larval stage, the mosquitoes will shed their skin and molt four times before changing to the pupal stage of their life cycle.

The pupal stage is where metamorphosis occurs, creating the adult mosquito. During the pupal stage they are no longer feeding as they have ingested enough nutrients to make the transition into an adult. This phase of the life cycle is similar to the cocoon of a butterfly although the mosquito pupa is fully active and mobile. Unlike the larval stage, the pupal stage of a mosquito is entirely aquatic, and the mosquito will perish if it is removed from the water.

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