Mosquitoes & Encephalitis

Mosquitoes, - most specifically the species Culex pipiens and Culex pipiens pipiens - are believed to be responsible for the transmission of the West Nile Like Encephalitis disease. Other mosquito species may also be a vector of this disease.

Mosquito Basics

Mosquitoes lay their eggs in "rafts" or groups in standing water or sometimes in dry areas that they anticipate will become wet. While many species lay eggs in large bodies of standing water, some take advantage of standing water in debris such as blocked gutters, tires, wheelbarrows, planters, swimming pool covers, ditches, sinkholes, and other land depressions.  

When the eggs hatch in response to a sufficient amount of water, the larva actually floats on the surface of the water. After a development period of 4 to 10 days, the larvae will pupate (enter the cocoon stage) while still in the water. In as little as a day, but sometimes weeks later, the adult (biting) stage emerges and remains floating on the pupal case until ready to fly off for its first blood meal.

The Encephalitis-related mosquitoes don't fly very far. If they feed on an infected bird and then bite a person, there is potential for transmitting the disease.  


As part of protecting the public health, officials take action to carefully monitor for mosquitoes carrying West Nile Like Encephalitis.  In some cases, caged chickens or other similar birds are placed in mosquito-prone areas and their blood may be checked for the virus on a regular basis. These birds are not affected by the virus but may have it in their bloodstream. 

Testing mosquitoes for the presence of diseases is another part of the process. Monitoring traps using fans and carbon dioxide (dry ice or cylinders) to attract the mosquitoes, help to determine if there is a level of mosquitoes present that requires control measures. 


Mosquitoes management may be best achieved using resource management.  

Mosquitoes breed in standing water and areas that are flood prone. Eliminating these harborages as mentioned above, is essential. Checking each property for ditches, clogged gutters, debris, etc. is a key part of the control.  Additional controls may include checking screens on buildings to be sure that biting adults are kept outside.

Another facet of management includes insect repellents, larvicides (to kill the larval mosquitoes in standing water) and adulticides.

Because children and the elderly are most vulnerable to the effects of West Nile Like Encephalitis, those groups should consider using insect repellents to protect them from insect bites.  Since mosquitoes are most active at night, people going out at that time need to be cautious.  Wearing long-sleeved garments and long pants if practical, can be helpful.

The Bug Clinic offers Mosquito Dunks as a general use larvicide for the public.  This round donut shaped product may be used to treat standing water in ponds, on top of swimming pool covers, in bird baths and in any other stagnant water.  This product is essentially non-toxic according to the manufacturer.  The active ingredient in the product is bacillus thuringiensis israelis or Bti.  This product is specific for mosquitoes and other insects whose larvae breed in standing water.

Adulticides may be applied to lawns and wooded areas to help kill mosquitoes.  Several insecticide concentrates may be applied for this purpose (check the label).  

We also offer an organic alternative to insecticides.  Dr. T's Nature Products produces an entirely organic formula called Mosquito Repelling Granules.  This is repellent to both mosquitoes and gnats and is poison free. According to the manufacturer, the product is actually beneficial to soil and the product has a pleasant odor.  A single application will last for two to three weeks or more.  We have sold the product for years now and have had mostly positive feedback.



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