Thursday, March 24, 2016

Controlling Mosquitos in Your Yard

Mosquito bites can be more than just annoying and itchy. They can carry viruses and make you very sick or potentially cause birth defects in the unborn children of pregnant women. Zika, Chikungunya , West Nile, Dengue, and St. Louis encephalitis are all viruses carried by mosquitoes and except for Zika have all occurred in the mainland United States. It is only a matter of time before the next virus Zika arrives. Mosquitoes become infected when they bite someone already infected with the virus. Infected mosquitoes can then spread the virus to other people. The major mosquito borne diseases are not common in the continental United States; however, Puerto Rico and the U.S. Virgin Islands have had large outbreaks.

We are fortunate that mosquitos die off or are dormant in the United States during the winter. So we have an opportunity to eliminate mosquito breading grounds ahead of the anticipate arrival of Zika and to protect us from West Nile Virus. The best way to prevent the Zika virus and the other mosquito borne viruses is to prevent mosquito bites in the first place. Management of adult populations for the Asian Tiger mosquito, Aedes albopictus, the carrier of the West Nile Virus and potentially the Zika virus is potentially more complicated than for other species due to tolerance to the insecticides malathion, temephos and bediocarb limiting the pesticides that can be sprayed on the adult populations. According to various mosquito studies the elimination of mosquito breeding habitat is the best approach to limiting the adult population for all species.

Mosquitoes lay their eggs in warm, still water. An adult female needs a blood meal to complete her life cycle and lay eggs. Often that blood meal comes from a human or other mammal. According to a study done by Dame and Fasulo in 2003, removing mosquito breeding habitat- any still water even as small as a bottle cap, can be an effective method for mosquito control.

Getting rid of mosquito breeding sites gets rid of mosquitoes. Eliminate any standing water on your property, change pet watering dishes, overflow dishes for potted plants, and bird bath water frequently. Do not allow water to accumulate in tires, flower pots, buckets, rain barrels, gutters, folds of tarps, trash, cups, bottle caps, wheel barrels, poorly drained areas, etc. Mosquitoes need only a bottle cap of water to breed. Most known types of mosquitoes do not travel far from where they hatch, so the actions of you and your neighbors can have a dramatic impact on your neighborhood mosquito populations. Check out the Maryland Department of Agriculture U-tube primer on eliminating the breeding ground for the Asian Tiger mosquito.

Because not all breeding sites can be eliminated, it may be necessary to use pesticides to kill the mosquito lava and the adult mosquito. Larvicieds, which kill mosquito larvae have been found to be more effective than adult spraying. The biological pesticide Bti (Bacillus thuringiensis var.israelensis) is commonly used in such places as storm drains and sewer treatment plants. Bacillus sphaericus works best in organically rich water in drains. Bti is proven to be effective and has low levels of toxicity to humans and wildlife.

By the time the larvae have moved into the third and fourth stage of metamorphosis, the Bti is less than 60 % effective, and additional larvicides may be necessary to eliminate the mosquito larvae. Methoprene (Altosid) may be necessary to kill larvae and prevent the use of pesticides aimed at adult mosquitos. Bti lasts approximately 30 days or longer if dry applied in heavier doses, and Methoprene lasts about 150 days. However, some studies find that Methoprene acts as an endocrine disruptor and causes deformities in wildlife.

Spraying using pesticides targeting adult mosquito populations is the least effective method of control and potentially the most damaging to human and animal populations. This type of spraying should only be done after carefully evaluating the effectiveness of the prevention strategies and the likelihood of pesticide-related illnesses and the contributing factors to a human epidemic of mosquito borne diseases.

Always choose the least dangerous pesticides. In general, synthetic pyrethroids have lower human health and environmental risks than organophosphates. Synthetic pyrethroids are pesticides derived from naturally occurring pyrethrins, taken from pyrethrum of dried Chrysanthemum flowers. They are designed to be more toxic with lower break down times than the naturally occurring pyrethrins. Though claimed to be selectively toxic to insects, synthetic pyrethroids are toxic to aquatic organisms, including fish in concentrations similar to those used for controlling mosquito. Many pyrethroids have been linked to the disruption of the endocrine system, reproduction and sexual development, interference with the immune system and the induction of breast cancer. The widespread use of pyrethroids can pollute water resources and affect non-target organisms and humans.

from Maryland Department of Agriculture

Remember that pesticides are only one part of a comprehensive mosquito management plan. Adult tiger mosquitoes are medium sized, black in color with distinctive white stripes. Tiger mosquitoes are persistent, moderately aggressive biters. The bite of the tiger mosquito is not painful and often goes unnoticed. Interrupted feeding is common and a female mosquito may bite the same person several times or move from person to person before the urge to bloodfeed is satiated. Tigers have a short flight range, about 100-200 yards. Tiger mosquitoes tend to remain near ground level in shaded areas, under decks and shrubs, basement stairswells and crawl spaces. The most effective way to prevent and control mosquito-borne disease is an integrated mosquito management program, and should include:
  • reduction of mosquito breeding sites,
  • surveillance and monitoring levels of mosquito activity, and where virus transmission is occurring,
  • use of pesticides to control both mosquito larvae and adult mosquitoes when found to be necessary, and
  • outreach and public education
In addition, use personal protection to avoid mosquito bites. Long pants, long sleeves and insect repellent such as DEET will reduce exposure to bites. The Asian tiger mosquito is a day biter that prefers legs and with feeding peaks early morning and late afternoon, so by limiting outdoor activities at dawn and dusk when mosquitoes are generally most active, bites can be avoided. The CDC also recommends staying inside as much as possible in places with air conditioning or that use window and door screens to keep mosquitoes outside.

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