Thanks to the rain, mosquitoes are thick
Russ Parman, assistant manager with the Santa Clara County Vector Control District, says because “of the abundance of rain we had earlier in the year we still have areas of standing water and damp environments that serve as perfect breeding grounds for mosquitoes and other flying pests.”
About 19 species of mosquitoes have been detected in the Bay Area.
By using planes equipped with sophisticated cameras, the district can spot problem areas from 5,000 feet. A recent trip detected 700 stagnant swimming pools in a 130-square mile area where there already were 1,500 pools known to exist.
Field technicians go door-to-door contacting owners about the pools and telling people about options.
Vector control districts will provide free mosquito-eating fish to those who no longer want to use or maintain their pools. Pool owners also can use a variety of control products or they can either get the pool back into swim condition, fill it in with sand, or remove it.
In the Bay Area the most common mosquitoes are the house mosquito (Culex pipiens), a short-range flyer of only a mile or two, and the encephalitis mosquito (Culex tarsalis), which can travel up to 10 miles.
Both are the primary vectors for West Nile virus. They generally feed on the blood of birds but occasionally bite humans and other mammals as well, which can spread the virus.
The mosquitoes are most active just after sunset and just before dawn.
Recently, the container-breeding, invasive Aedes genus mosquitoes have become a significant concern. They are easily transported by hitch-hiking on vehicles and containers, and can breed in as little as a bottle cap full of water.
Unlike the more common mosquitoes, Aedes mosquitoes bite during the day, love to feed on humans and can transmit several severe and sometimes fatal illnesses including Zika, chikungunya and dengue viruses . They can breed indoors as well as outdoors.
Two of concern are the yellow-fever mosquito (Aedes aegypti) and the Asian tiger mosquito (Aedes albopictus). The yellow-fever mosquito is deep brown with a fiddle-shaped marking on its thorax and has prominently banded legs. The Asian tiger is jet black with a white stripe down the middle of its back and also has banded legs.
The invasive Aedes mosquitos are now well established in both Central and Southern California. With the frequent travel and transport of vehicles and goods, experts believe it is only a matter of time before they take hold in the Bay Area. In recent years there have been brief infestations in both San Mateo and Alameda counties.
Along with increased mosquito activity, you might also be seeing swarms or large populations of midges. Midges (Chironomidae) resemble mosquitoes but are actually small flies. You might see mating swarms in open areas. Although they can be a nuisance in large numbers, they do not bite.
Take a walk around your property and empty any collections of standing water you find. Check all plant pots, trash cans, rain gutters and any water catchment systems you may have set up. As the temperature starts to heat up, we need to be even more vigilant.
If you see these mosquitoes, find dead birds, or know of unattended pools, call the district in your area.
- Santa Clara, 408-918-4770
- Contra Costa County, 925-771-6196
- Alameda County, 510-783-7744 (In Albany, call 510-567-6800.)
by UC Master Gardener Rebecca Jepsen
Mosquito Illustration: California Master Gardener Handbook
This article first appeared in the June 25 issue of the San Jose Mercury News.
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