Guide to Mosquito Abatement in Winter
People rarely encounter mosquitoes in winter. The main reason for this is that mosquitoes are usually inactive in winter months, retreating to abandoned buildings, sewers, leaf piles and other wind free havens to diapause (a term similar to “hibernate”) for the winter. However, even cold weather is not a guarantee against mosquito activity. This guide is to help you manage any winter problems and to prepare for spring when mosquito populations reestablish themselves
What to Look For
Standing water is still the most important condition to watch out for. Look for standing water at any time but especially after rains. Mosquitoes need immobile water with some organic matter to hatch and grow. As little as one spoonful of water can breed mosquitoes. After winter rains start, water can accumulate not just in obvious spots but in other places — tires, planters, trays under potted plants, wheel barrels, openings in rain barrels, watering cans, garbage cans, tubs, other containers and shaded areas, especially in places that see little foot traffic. Standing water can also accumulate under trees as rain or even fog drips from their branches. A discarded plastic bag in the right position can catch rainwater and breed mosquitoes. Palm fronds can hold enough water to breed mosquitoes. If there are old tires in your area, they should be disposed of properly. Because of their irregular shape, tarps draped over outdoor furniture or equipment often hold standing water.Clogged drains and basins may become pools of standing water in the rainy season.
In all of these places mosquitoes can breed. The life cycle of the mosquito varies according to weather. In temperatures consistently over 70 F they may become adults within a week after hatching. Fortunately winter rains are usually associated with cooler weather. However, even in winter, warm spells can occur after rains. And even when temperatures stay cool, mosquito eggs can hatch and develop into adults in about three weeks. To be safe and sure, dump or drain all standing water within a week.
It is important to note that some mosquito species lay their nearly microscopic eggs before they go into diapause. The eggs stay dormant until the weather warms up at which point they hatch. If standing water is eliminated in winter, the initial mosquito populations in spring will be small and will remain so with ongoing Integrated Pest Management.
Harborage — To control mosquitoes in winter and prepare for the coming spring, knowing mosquito harborage is almost as important as locating standing water. Mosquitoes spend their winter diapause in abandoned buildings, caves, hollow logs, animal burrows, piles of decaying leaves, and other dark and windless places. Overgrown shrubbery, while not considered a major harbor for wintering mosquitoes, can harbor other pests. Managing these environments by cleaning or clearing away debris can decrease next year’s mosquito population. In addition, mosquito harborage can also shelter other pests such as rats and mice. So eliminating harborage for mosquitoes offers the added benefit of keeping away other pests.
Know the enemy!
Recognize mosquito larvae and pupae. Photographs of mosquito larvae and pupae are easily found on the Internet. After hatching, larvae are almost microscopic but will grow to about an inch in length. They are usually light brown but in the water may appear black due to lighting. Larvae feed on the bottom or below the surface, then wiggle to the surface where they breathe air. As they mature, they will start to curl. Eventually they will stay at the surface in a curled position. This is their pupae stage and shortly after they will become adults and fly away from the water. Some species never fly more than a mile from their birthplace while salt marsh species may fly over 40 miles away.
Garden Ponds
Garden ponds do present some challenges. Ponds with some mechanical means of agitation can keep water in motion. Moving water will discourage female mosquitoes from laying their eggs. However, there are no guarantees and occasionally a few perseverant pregnant mosquitoes will lay their eggs on gently moving water. If your pond has moving water, you should still observe it, especially where the water is in less motion.
By taking care of standing water and harborage, you can not only prevent the rare occurrence of encountering a mosquito in winter, you can decrease their numbers in the coming spring. We at Pestec wish you a safe, happy and pest free holiday season!
by Howard Williams, Veteran Mosquito Biker
MosquitoSF.com is the offical page of the San Francisco Mosquito Abatement Courier (MAC) Team.
The MAC Team is made possible by SF Water and Pestec Integrated Pest Management.