April 13, 2019
Winter was generous this year, with record rainfall in many parts of Marin County. While we celebrate the abundance of rain and snow for our watersheds, it can also give mosquitoes a boost. There are 23 species of mosquitoes in Marin and Sonoma, and they are present year-round.
While the Marin/Sonoma Mosquito and Vector Control District (MSMVCD) protects our large tracts of land, the home gardener has a pivotal role in prevention and reduction of mosquitoes in our neighborhoods.
The most effective prevention strategies address the mosquito in the larval stage. Once an egg is in contact with water, it develops into a larva and lives underwater, getting oxygen through a tube at the surface. At the end of the next development stage, pupae sprout six legs, two wings and a tubular feeding organ for eating, called a proboscis, and fly off to find nectar for energy.
Female mosquitoes need protein from blood to develop their eggs. It’s through this feeding process that pathogens and parasites can be transferred in the saliva of the mosquito to the host, be it man or beast. Some of the diseases mosquitoes spread to humans include West Nile virus, encephalitis, and malaria.
Spring is “tree hole” season as the mosquitoes responsible for the spread of the parasite that causes heartworm in dogs lays their eggs in bark and tree holes in the winter and pupate in April.
The tiny larvae swimming in water at these early life stages may be hard to see but “mosquitofish” can find them easily and eat hundreds of larvae every day. Stocking ponds and small lakes with no connection to natural waterways with mosquitofish can reduce the initial population and will be available through the MSMVCD in May.
Mosquitoes only need half an inch of water in any sized container to breed so eliminating sources is critical. Since the life cycle of the mosquito is short, rinsing out birdbaths, bowls and pot saucers on a weekly basis is a good idea. Mosquitoes breed in water that might collect in leaves, puddles, hose bibs, drains, old tires, and your pet’s water bowl. Inspect your garden weekly for any accumulation. Turn your buckets upside down, hang your shovels vertically, and watch for pooling irrigation.
If you have a pool, make sure the cover is dry and the chemical quality of the water is maintained. Check your gutters, cleaning out debris and removing pooling water. If you have saucers under your potted plants, drill a hole in the bottom or pack them tightly with sand or fine gravel. For small fountains and ponds, add a “mosquito dunk” which contains BTI, a safe bacteria that will destroy the larvae’s digestive system.
If you find adult mosquitoes in your yard, contact the Marin/Sonoma Mosquito and Vector Control District. They will send a technician to your home for a free assessment. They’ll identify the pest to ensure they truly are mosquitoes and not a midge, which looks very similar to a mosquito. If their assessment requires traps or treatment, they provide those services. Check out the website at msmosquito.com for additional information and ideas for prevention, or attend an open house from 11 a.m. to 3 p.m. May 18.
Having a garden party and want to deter unwanted guests? Insecticide sprays are not effective for adult mosquitoes and are designed to kill indiscriminately, so they also kill honeybees, butterflies and other beneficial insects. Citronella candles offer some repellency but are not adequate for large areas as they dissipate quickly. For small patios, placing rotating fans pointed away from the patio can keep the area free of the weak-flying mosquito.
As gardeners we have an important role in the prevention of mosquito-borne disease in animals, dogs and humans. By inspecting our gardens for breeding opportunities we can help control mosquitoes.