"These are a major pest and they are possible transmitters of WNV," said Deborah Bass, public affairs manager for the Contra Costa Mosquito Abatement and Vector Control District (CCMVCD). "We are getting very high amounts of them."
Because officials have been unable to locate the outbreak's source and kill the mosquito larva, spraying the adults became necessary. However, the district has ruled out the Delta Coves construction site on Gateway Road as a source for the proliferation of the Ochlerotatus melanimon, a mosquito that typically breeds in irrigated pastures and fields, Bass said. The female melanimon is a vicious and painful biter.
Residents started noticing an increase in the mosquito population a couple weeks ago. What was unusual is that these mosquitos appeared throughout the day, not merely at dusk. "They are so bad, I couldn't even go outside in the middle of the day without being bit," said longtime Bethel Island resident Bertha Sharp, whose property abuts one of several drainage ditches that crisscross the island. "They bit my hands so badly."
In addition to spraying, the CCMVCD has restocked mosquito-larvae-eating fish, dispersed pellets that kill larvae and are monitoring the insect population by means of strategically-located traps.
"We do whatever is necessary to protect public health," Bass said.
There are 23 varieties of mosquitos in Contra Costa County, but only two in the Bethel Island area. In addition to the melanimon, there is the more common Culex tarsalis mosquito that swarms at dusk. Also known as the western encephalitis mosquito, this bug is the principal transmitter of WNV. And while the melanimon has the potential to transmit the disease, none have tested positive so far. In all species of mosquitos, it is the female that craves blood for its protein content, which is used to develop her eggs. Both male and female mosquitos actually feed on plant juice, Bass said.
The district will continue trapping and testing and urge the public to protect themselves with spray containing DEET or Picaridin. Bass said it also is extremely important to eliminate any standing water where mosquito larvae can develop.
To date, eight human cases of WNV, as well as numerous infected birds and squirrels, have been reported in Contra Costa County. For more information about what the district is doing in your neighborhood, log onto www.ccmvcd.dst.ca.us. If you suspect an outbreak or want to talk to someone from the district, call 685-9301.