It’s a long way to the official start of summer, but mosquitoes flourish just the same
It’s a long way until Memorial Day, the unofficial start of summer, but thanks to our warm, dry weather so far in 2015, Contra Costa County residents are already breaking out the t-shirts and shorts while mosquitoes are making their presence known in March rather than May.
“Adult mosquitoes are out a good six to eight weeks early,” says Contra Costa Mosquito & Vector Control District Mosquito Program Supervisor Sheila Currier.
Each spring, Currier and her vector control team visit neighborhood parks to make a preemptive strike against Western tree hole mosquitoes which can transmit canine heartworm disease. These mosquitoes (Aedes sierrensis) typically lay their eggs along the edges of rot holes that can develop in certain species of trees including oak, laurel and eucalyptus. When winter rains fill the holes with water, the eggs begin to develop into young mosquitoes that eventually leave the nest as flying adults in the springtime. District staff fill each hole with an absorbent material that prevents the water from collecting so that the mosquitoes cannot thrive. But much to their surprise this year, District inspectors not only found the larvae of the tree hole mosquitoes developing, they also found the larvae of one of the mosquitoes (Culex tarsalis) capable of transmitting West Nile virus.
“The mosquitoes that can transmit West Nile virus typically start showing up in mid-May to early June. To see them in early March was surprising and meant that we had to start checking and treating neglected swimming pools and ponds earlier because they can be primary sources of these mosquitoes,” says Currier.
Sure enough, District inspectors found backyard sources, including neglected swimming pools with both young and adult mosquitoes with the latter prompting the District’s staff to initiate control efforts that usually don’t happen until late spring or early summer.
Along the county’s coastline, Currier says, another summertime mosquito, saltwater marsh mosquitoes, are already developing as well because the weather has been warm and there has been very little Sierra snowpack to dilute the salinity of brackish coastal water. That means, as long as the salt content remains high, these coastal, day-biting mosquitoes that were plentiful in 2014, may once again begin teeming into coastal communities.
California’s new proposed water restrictions go into effect in April that may unintentionally help alleviate mosquito sources by restricting landscaping and recreational water usage. With 2015’s mosquito season off to such an early start, every water source counts.
Published by Contra Costa Mosquito & Vector Control
