September 13, 2011 Report by Manager Jenny Mullins: Cool weather in May and June of 2010 and this year helped to limit the spread of West Nile virus in our state.  So far this year only two mosquito samples in Washington have tested positive: one in mid-August in Yakima County and one in early September in Grant County.  In 2010, 126 mosquito samples and 2 birds tested positive for the disease in Grant, Benton and Yakima Counties.  Grant and Chelan counties each had one human case of the disease in 2010, but the Chelan County case is believed to have been acquired during travel in Colorado.  (Chelan County had one other travel-related human case in 2006.) This year larva were first found on March 29 and larvicide treatments began on March 31.  Unusually high precipitation in March resulted in a a very full snowmelt area against the hillside east of East Leavenworth Road.  Treatments there began on April 11 when 3rd instar larva were found: the area of standing water there was over 10 acres, a District record for this area.  As a result, assistant Barry Moats was brought on to treat other areas while this area was being treated.  In 2006, high rains in May refilled this site and a discontinuous portion of this site was missed, resulting in our last aerial adulticide spray treatment.  My experience this year has greatly increased my familiarity with this site and where to check for standing water. Other unusually high sites this year were the wetland behind the gravel pit which was overflowing in July and the wetland between Prowell Street and East Leavenworth Road which had quite a bit of water well into August.  The latter wetland (or a pipe leak discovered by Barry Moats nearby) was responsible for our highest mosquito catch for both 2010 and 2011.  18 mosquitoes were caught here overnight and picked up on August 12.  14 were Culex mosquitoes including 9 Culex tarsalis.  Normally I would have tested these mosquitoes  for West Nile virus, but at that point no virus had been detected in Washington, Oregon and Idaho. I did not have any VecTest materials on hand (kits only last 18 months from manufacture) and decided not to take the expense of ordering them.  I collected more mosquito samples on September 9, but no trap caught more than two mosquitoes then, so trapping has been ended.   Although we did not keep our maximum trap count or Culex count below the records set in 2010, we did manage to bring the second highest trap count down to 11 (Waterfront Park), and our second highest Culex count down to 3 (also at Waterfront Park).  In 2010, the highest and the second highest trap counts were both 12 and the highest Culex count was 7 caught at Waterfront Park followed by 5 at Mine Pond.  Higher water levels this year reduced the need for puddle treatment along the river bed and may have contributed to low Culex counts in general.  Prior to 2010 we always had at least one trap catch of 30 or more mosquitoes each year and our top two Culex counts both reached at least 10.  We are pleased that overall our control program has been very successful despite high water levels this year. The high snowpack in the mountains led us to hire an extra assistant Michael Darlington who began work in May and continued thru early July. His work coincided well with the highest snowmelt periods. The snowpack wass similar to that of 2008 when the city parks flooded in May and of 2002 which had such an extended high water period (and so many resulting mosquitoes) that the ballot measures creating and approving funding for our district passed handily.   Assistants work part-time 5 to 20 hours a week depending upon the need and thus we are well equipped to handle the fluctuating amount of standing water. If another La Nina (and high snowpack) next winter materializes as predicted we may be hiring an extra assistant again next year. Last year assistant Barry Moats began working for us.  He has worked the majority of both the 2010 and the 2011 seasons ensuring that larviciding occurs in a timely manner.  His efforts helped to bring trap counts to their lowest levels yet:. In past years we have always had at least one trap catch of 30 or more mosquitoes Our district historically has had large numbers of Aedes vexans mosquitoes.  Their larva are dominant during high water periods since the females lay their eggs on land in anticipation of flooding. However Culex tarsalis and Culex pipiens are the species of greatest concern for the transmission of West Nile virus. These species lay their eggs on standing water and will increase in numbers through August so residents are urged to police their yards and drain any standing water in tarps, tires, buckets and the like weekly.  Please drain and cover or dispose of any rimless tires.  Call 548-3316 if a site in the district is not drainable and requires treatment. 2009 was the worst year to date for West Nile virus in Washington state.  346 mosquito samples tested positive for the virus that year.  Sampling began in late May and immediately positive samples were found in Yakima County.  During 2009, 38 people, 72 horses, 1 dog, and 22 birds also tesed positive for the virus. Most of the human cases were serious including symptoms such as meningitis, encephalitis, paralysis and one death.  In 2008, West Nile virus was found in 57 mosquito pools, 3 people,  41 horses,  1 dog and 24 birds. Since the Culex mosquito is the main carrier of this disease, in 2008 I acquired a stereomicroscope and learned to identify Culex pipiens and Culex tarsalis, the two Culex species present in our area. When Culex numbers reach 10 or more at a trap site (or 6 or more Culex tarsalis) these mosquitoes are tested using VecTest.  In 2008 and 2009 all the test results were negative for West Nile virus in our district. In 2010 there were not enough mosquitoes for testing to be needed.  Culex tarsalis mosquitoes feed equally on birds and mammals while Culex pipens prefer birds.  Since Culex tarsalis is more likely to transmit the virus to humans we normally use a lower threshold for West nile virus testing: six Culex tarsalis mosquitoes in one trap versus 10 of either Culex species.  The numbers required are most likely to occur in August when the population of Culex peaks.  If a positive sample is obtained then a prompt aerial spray contract would be likely.    Historically the floodwater mosquito Aedes vexans has been the predominant mosquito in our area.  This mosquito lays its eggs on land in anticipation of flooding due to snowmelt or a rising water table.  Due to its preference for mammals it is only an incidental carrier of West Nile virus.  Other species of Aedes are important vectors of malaria, dengue fever and other diseases which do not require birds for their amplification but these diseases are not expected in our area in the near future.  Assistants help us to deal with periods of high water flow when the water table rises to produce more larval habitat. All assistants possess a pesticide applicators license so that they can work independently.  Barry Moats started his first season with us in 2010.  He is responsible for most of the East Leavenworth Road area as well as Prowell Road.  Bruce Hill of Wenatchee joined us in 2007 and stayed through 2009, while David Wood worked from 2004 through 2006.  Their efforts helped to demonstrate that ground larvaciding can be successful even during high water years like 2006 and 2008. We encourage residents to call 548-5904 to report sightings of two or more mosquitoes within the Leavenworth District (within 2 miles of Leavenworth). This allows us to track down small backyard breeding sites for the Culex mosquito which lays its eggs on water and is most likely to carry the West Nile virus because it feeds on both birds and mammals.  Such sites have the potential to produce thousands of mosquitoes so residents are urged to check their property regularly for standing water. Barrels, buckets, tires and tarps are common culprits.  Be especially aware of containers which will be refilled by your sprinklers and make sure that no site has standing water for more than a week. Any time is a good time to make sure that screens are in good repair.  As summer arrives be sure to use an effective repellent during those times when contact with mosquitoes is likely. Do not allow mosquitoes to bite you! Our main larvacides are Bti, Bs, and Agnique (a monomolecular film).  We use Bti (Bacillus thuringiensis israelensis) the most: it works well on both Culex and Aedes and usually kills larva overnight by dissolving their midgut after they ingest it. Other strains of Bt are used to control a variety of forest and agricultural pests and are commonly used by organic farmers. In its granular form Bti is our cheapest pesticide at about $16 per acre. It also comes in longer lasting doughnut-shaped briquets which are used in sites under 1000 square feet. Our cheapest longer lasting material is Bacillus sphaericus (Bs). It costs about $100 per acre and works in a similar manner to Bti but is not effective on Aedes the floodwater mosquito which lays its eggs on dry land and then hatches in great numbers when flooded. Agnique, a monomolecular film drowns pupa by reducing the surface tension of the water. The rotation of various larvacides helps to reduce the likelihood of pesticide resistance.  In 2006 we began using methoprene, a hormone which prevents the completion of metamorphosis in mosquitoes. The formulation we use provides control for up to 30 days. We use it in storm drains and hard to reach areas (such as islands which will become inaccessible) where the presence of pupa does not bother us. In 2009 we added a combination larvicide, Vectomax to our arsenal.  Vectomax combines Bti and Bs to allow long-lasting control of Culex with the added benefit of Bti to control Aedes and to prevent the development of Bs tolerance in Culex. Storm drain treatment is a very important part of our disease prevention program and that of many other cities. The storm drains are treated once a month by bicycle along with other small sites in Leavenworth using methoprene, Bs, or Vectomax. Most of our district has not been sprayed with adulticide (malathion) since 2003. About an eighth of the district was sprayed in 2006. Complaints help us to track down mosquito breeding areas. Complaints helped us to locate untreated storm drains, tiny ponds, tires and easily drainable tarps, buckets, boats and the like. Call us at 548-5904 if you see two or more mosquitoes in an evening.  In your message please leave your phone number, the location of the site and a description of the problem (adult mosquitoes or standing water).  Residents need to be sure to check their yards for any standing water: standing water collected by any container will attract the Culex mosquito which lays its eggs on water. Drain the water if possible, otherwise call us at 548-5904 for treatment.  In 2005 at least three complainants were inadvertantly breeding mosquitoes on their own property: in an old bathtub, a container for cuttings, and in a tarp. In other cases, the neighbors were breeding mosquitoes: in an untreated swimming pool, a horse trough and a large cooking pot. If you have a swimming pool, then make sure it is empty or chemically treated.  If you have a horse trough, make sure the water is fresh and if unable to do this or if you will be away on vacation make sure to get Bti briquets from us for treatment every 3 to 4 weeks. Horse owners are reminded to vaccinate their horses: a two shot series is needed the first year, followed by a booster shot each year thereafter. For the best protection these shots should be completed in the spring. West Nile virus is fatal in about 30% of those cases diagnosed in horses. Although West Nile Virus is not usually deadly in humans, its effects can be quite debilitating.  All ages can be affected but the average age (median and mean) of all cases is in the late 40's with  an average in the late 50's for the worst symptoms.  In order to avoid the disease, avoid contact with mosquitoes. This can be done by maintaining home screens and by avoiding mosquito laden areas and wearing long sleeves, particularly in the evening. There are several effective repellents on the market now: products containing DEET have endured the test of time, the military uses a 33% DEET formulation: higher concentrations may irritate more sensitive skin, formulations between 7 and 20% are quite effective as well. For those who are apprehensive about the use of DEET, products containing Picaridin or oil of lemon eucalytus also offer long-lasting protection. Why does our district put so much effort into education (to reduce larval habitat) and larvaciding as opposed to adulticiding? There are several reasons: enough to persuade those of almost any political persuasion. Because larvaciding is applied when mosquitoes are most concentrated, it is cheaper and more likely to be effective. (Where possible habitat reduction is by far the cheapest and most effective route.) The materials used for larvaciding are much better targetted to the mosquitoes and thus have much less impact on other species and much less risk to humans. At present there are no documented cases of mosquitoes becoming resistant to Bti, whereas resistance to malathion and other organophosphates is not uncommon. Finally larvacide kills the mosquito before it has a chance to transmit disease.